DEVELOPMENT OF SOIL-EPS MIXES FOR …eprints.qut.edu.au/16542/1/Hema_Kumar_Illuri_Thesis.pdf ·...

DEVELOPMENT OF SOIL-EPS MIXES FOR

GEOTECHNICAL APPLICATIONS

HEMA KUMAR ILLURI

A thesis submitted for the degree of

Doctor of Philosophy

School of Urban Development

Centre for Built Environment and Engineering Research

Queensland University of Technology, Australia

2007

iii

To my parents,

(late) Illuri Harinatha Babu Rao and

Illuri Hymavathy.

v

STATEMENT OF ORIGINAL AUTHORSHIP The work contained in this thesis has not been previously submitted to meet

requirements for an award at this or any other higher education institute. To the

best of my knowledge and belief, the thesis contains no material previously

published or written by another person except where due reference is made.

Signed: _________________________________

Hema Kumar Illuri

Date: ___________________________________

vii

CONTENTS

Statement of original authorship v Abstract xi Acknowledgements xiii List of Figures xv List of Tables xxv Nomenclature xxvii List of publications xxix

CHAPTER 1 INTRODUCTION 1 1.1 Background 1 1.2 Hypothesis and focus of the research 5 1.3 Objectives of the research 6 1.4 Organisation of the thesis 7 CHAPTER 2 EXPANDED POLYSTYRENE AND ITS UTILISATION 9 2.1 Expanded polystyrene 9 2.2 General uses and properties of EPS 11 2.3 Applications of EPS in geotechnical engineering 13 2.4 Soil-EPS mixes as lightweight fill materials 17 2.5 EPS applications in Australia 30 2.6 Management of waste EPS 32 2.7 Summary 36 CHAPTER 3 EXPANSIVE SOILS AND THEIR TREATMENTS 39 3.1 Expansive soils 39 3.2 Factors influencing mechanisms in expansive soils 40 3.3 Distribution of expansive soils in Australia 43 3.4 Characteristics of expansive soils 44 3.5 Effects of expansive soils on different structures 46 3.6 Expansive soil treatment options 48 3.7 Possible use of soil mixed with EPS beads 61 3.7 Summary 63 CHAPTER 4 SCOPING STUDIES WITH A DREDGED SOIL 65 4.1 Dredged soils 65 4.2 Waste EPS 68 4.3 Dredged soil from Port of Brisbane 72 4.4 Preparation of dredged soil and EPS mix 73 4.5 Optimum mix proportion of soil-EPS mixes 74 4.6 Compaction properties of soil-EPS mixes 76 4.7 Strength behaviour of soil-EPS mixes 80 4.8 Swell-shrink studies 88 4.9 Need for further studies with reconstituted expansive soils 91 4.10 Summary 92

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CHAPTER 5 SAND-BENTONITE (SB) MIXES 93 5.1 SB mix as a model material for expansive soil 93 5.2 Material properties 97

5.3 SB mix preparation 99 5.4 Atterberg limits 99

5.5 Hygroscopic moisture content 103 5.6 Compaction behaviour 104 5.7 Optimum lime content 107 5.8 Preparation of Soil with EPS (SWEPS) mixes 110 5.9 Specific gravity of SWEPS mixes 111 5.10 Summary 112

CHAPTER 6 COMPACTION OF SOIL WITH EPS (SWEPS) MIXES 113 6.1 Compaction studies 113 6.2 Experimental programme 114 6.3 Compaction curves 116 6.4 Effects of EPS on maximum dry unit weight 119 6.5 Effects of EPS on optimum moisture content 121 6.6 Effect of degree of compaction 122 6.7 Comparison of compaction characteristics of SWEPS mixes with other composite soils 122

6.8 Volumetric proportions 124 6.9 Predictive model for dry unit weight 127 6.9 Summary 128

CHAPTER 7 SWELLING AND SHRINKAGE STUDIES ON

SWEPS MIXES 131 7.1 Compaction of SWEPS specimens 131

7.2 Swelling characteristics of SWEPS mixes 132 7.3 Cyclic swelling 155 7.4 Effect of EPS and lime on swelling 161

7.5 Shrinkage characteristics 164 7.6 Summary 174 CHAPTER 8 SHEAR STRENGTH OF SWEPS MIXES 177 8.1 Direct shear tests 177 8.2 Unconsolidated-Undrained triaxial tests 197 8.3 Effect of lime on the shear strength of SWEPS mixes 228 8.4 Summary 232 CHAPTER 9 SUCTION AND DESICCATION STUDIES 235 9.1 Suction studies 235 9.2 Desiccation studies 246 9.3 Summary 268

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CHAPTER 10 HYDRAULIC CONDUCTIVITY, COMPRESSIBILITY AND WATER BALANCE ANALYSIS OF A SWEPS MIX 269 10.1 Hydraulic conductivity 269 10.2 Compressibility characteristics 273 10.3 Water balance analysis using Visual HELP software 279 10.4 Summary 290 CHAPTER 11 CONCLUSIONS AND RECOMMENDATIONS 291 11.1 Scientific contribution from this research 291 11.2 Engineering applications 292 11.3 SWEPS mix deign criteria 294 11.4 Conclusions from this research 296 11.3 Recommendations for further studies 298

REFERENCES 301 APPENDIX 327

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ABSTRACT Global concern about the environmental impacts of waste disposal and stringent implementation of environmental laws lead to numerous research on recycled materials. Increased awareness about the inherent engineering values of waste materials, lack of landfill sites and strong demand for construction materials have encouraged research on composite materials, which are either fully or partly made of recycled materials. This trend is particularly strong in transportation and geotechnical projects, where huge quantities of raw materials are normally consumed.

Owing to the low mass-to-volume ratio, disposal of Expanded Polystyrene (EPS) is a major problem. In addition, EPS recycling methods are expensive, labour intensive and energy demanding. Hence, this thesis is focused on the development of a new soil composite made by mixing recycled EPS with expansive clays. Given the high cost of damage to various buildings, structures and pavements caused by the unpredictable ground movements associated with expansive soils, it has been considered prudent to try and develop a new method of soil modification using recycled EPS beads as a swell-shrink modifier and desiccation crack controller. The innovative application of recycled EPS as a soil modifier will minimise the quantity of waste EPS destined to the landfill considerably.

An extensive experimental investigation has been carried out using laboratory reconstituted expansive soils - to represent varied plasticity indices - consisting of fine sand and sodium bentonite. Three soils notated as SB16, SB24 and SB32 representing 16%, 24% and 32% of bentonite contents respectively were tested with four EPS contents of 0.0%, 0.3%, 0.6% and 0.9%. The tests performed include compaction, free swell, swell pressure, shrinkage, desiccation, shear strength and hydraulic conductivity. All the tests have been performed at the respective maximum dry unit weight and optimum moisture content of the mixes. It has been observed that by mixing of recycled EPS beads with the reconstituted soil, a lightweight geomaterial is produced with improved engineering properties in terms of dry unit weight, swelling, shrinkage and desiccation.

The EPS addition depends on the moulding moisture content of the soil. With increasing moisture content, additional EPS can be added. Also, there is a reduction in dry unit weight with the addition of EPS. Furthermore, the reduction of swell-shrink potential and desiccation cracking in soils, for example, is related to the partial replacement of soil particles as well as the elasticity of the EPS beads. There is a reduction in shear strength with the addition of EPS to soils. However, mixing of chemical stabilisers along with EPS can enhance the strength in addition to improved overall properties.

Keywords: Expanded Polystyrene, EPS, expansive soil, recycled materials, swelling, shrinkage, desiccation, cracking, soil stabilisation, soil replacement.

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ACKNOWLEDGEMENTS The work described in this thesis was made possible by the award of an Australian International Postgraduate Research Scholarship (IPRS) administered by Queensland University of Technology (QUT), Brisbane, which is gratefully acknowledged.

During the course of Ph.D., the author is privileged to have encouragement, support and patience of many people and organisations inside and outside of QUT and wishes to express his heartfelt thanks to all of them.

In the first instance, the author is glad to take this opportunity to express his profound sense of gratitude and indebtedness to his perspicacious principal supervisor, Dr. Andreas Nata-atmadaja, for his enthusiastic and expert guidance, continuous help, valuable assistance, encouragement, constructive suggestions and positive criticisms throughout the course of this work. His immense patience and availability for comments whenever approached, even amidst his heavy pressure of work throughout the entire period of this research, deserves grateful appreciation. The author falls short of words while paying gratitude to him for his patience in checking the thesis draft.

The author also wishes to express his sincere thanks to Dr. Les Dawes for kindly agreeing to serve as associate supervisor and also for his valuable advice and assistance. Special thanks are extended to Dr. Jon Bunker and Assoc. Prof. Kunle Oloyede for their advice and suggestions.

Sincere thanks are extended to Prof. Mahen Mahendran for providing guidance, assistance and suggestions, in the initial phases without which I have missed this opportunity of pursuing Ph.D. at QUT and also for financial support during the course of the work. Special thanks are extended to Assoc. Prof. Ashantha Goonetilleke, Prof. Luis Ferreira and Prof. David Thambiratnam, for their generous financial support for attending the conferences and for their help and valuable suggestions.

The authour is grateful to the School of Urban Development (and the former School Civil Engineering), Centre for Built Environment and Engineering Research (CBEER) in the Faculty of Built Environment and Engineering at QUT for providing a stimulating environment for research. Moreover, the financial support provided as living allowance throughout the candidature by CBEER, especially Prof. John Bell, is also duly acknowledged.

The Expanded Polystyrene (EPS) was supplied by Queensland EPS recycling centre. The author wishes to express his thanks to Mr. Leo Sines for his help in this regards.

xiv

Special thanks are also extended to Mr. Trevor Laimer, Mr. Arthur Powell and Mr. Terry Beach, for their technical assistance during the course of experiments in this research.

It is pleasure to thank fellow post-graduate students and friends for their support and contribution to this research, especially special thanks are extended to Dr. Prasad Gudimetla, for his comments which enhanced the thesis, Mr. P. Praveen, for his help in extracting the cracking areas using MATLAB®, Mr. Reddy and Mr. Sivaram for their constant support and help during the course of this research. Further, the author extends his profound thanks to Mrs. Lynda Lawson, for her generous help in thesis correction.

A very special vote of thanks goes to Chancellor G. Viswanathan, Vice-Chancellor, Dr. P. Radhakrishnan, and Dr. D.V.S. Bhagavanulu of VIT University, Vellore, India and Dr.U.Lazar John, Principal, Jyothi Engineering College, for their constant support and encouragement extended to the author for pursuing Ph.D. at QUT.

The author would like to acknowledge the contribution of his family, especially his beloved mother, Mrs. I. Hymavathy, for her sacrifices and prayers. Further, special thanks are due to the authors’ father-in-law, Mr. Ch. Rambabu, and mother-in-law, Mrs. Ch. Santha Kumari for their wishes and blessings.

Finally the author expresses his deepest gratitude to his wife Sunitha, for her forbearance, for providing unswerving support, encouragement and tremendous help with cheerful smile during the time spent in this work. Also he is grateful to his son Karthick for his endurance and understanding.

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LIST OF FIGURES Figure Title Page 1.1 EPS packaging products 2

2.1 Generalised diagram for EPS geofoam embankment 14

2.2 EPS being placed over soft ground 15

2.3 Placement of lightweight fill 15

2.4 Construction process for port and harbour structures 19

2.5 On-site mixing process (a) Mixing of EPS beads and stabiliser

and (b) Mixing machine 20

2.6 Central mixing plant (a) Plant mix method and (b) Sealed

batch type mixing plant 21

2.7 Relationship between wet unit weight and mixture ratio of

EPS beads 23

2.8 Sections of caissons and testing cases 23

2.9 Wet unit weight of Soil-EPS composite immediately after placing 24

2.10 Change in wet density after one year 25

2.11 Change in apparent unit weight with mixing rate of beads 25

2.12 Relationship between the wet density and UCS 26

2.13 Unconfined compressive strength with depth 27

2.14 Stress-strain curves for a dredged soil mixed with EPS beads

at a moisture content of 2.5 times liquid limit 28

2.15 Stress-strain curves for the Araike bay mud at liquid limit 29

2.16 Stress- strain curves for the sand mixed with EPS beads with

moisture content 10% above the optimum moisture content 29

3.1 Distribution of expansive soils in Australia 43

3.2 Shrinkage and cracking of expansive soils 44

3.3 Wetting and loss of strength in expansive soils 45

3.4 Relationship between swelling pressure and clay content at

same initial moisture content 53

3.5 Relationship between swell and square root of time for different

stiffnesses at surcharge of 7 kPa. 54

3.6 Variation of swelling strain with fibre dosages on wet and dry of

optimums 56

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Figure Title Page

3.7 Volumetric swell strain of fibre treated soil compacted at 100% of

dry unit weight 57

3.8 Variation of crack sizes and distribution with and without fibres 58

3.9 Crack rduction wih various fibre contents 59

3.10 Variation in swelling with tire chips 60

3.11 Retaining wall backfill treatment 62

4.1 Produce boxes (a) before crushing and (b) after crushing 69

4.2 Size and shape of the EPS beads (a) pre-puff beads and

(b) recycled beads 70

4.3 Particle size distribution curve recycled EPS pieces 70

4.4 Reduction in size of specimens before and after heating at 80° C 72

4.5 Compaction curves for the dredged soil tested 72

4.6 Dredged soil – EPS beads composite before compaction at

45% moisture content 74

4.7 Cross section of Soil-EPS mix at OMC (39%) (a) 0.5% EPS,

(b) 1.0% EPS and (c) 1.25% EPS 75

4.8 Cross section of Soil-EPS mix at 45% water content (a) 1% EPS

and (b) 2% EPS 76

4.9 Cross section of Soil-EPS mix at 50% water content (a) 1% EPS,

(b) 2% EPS and (c) 3% EPS 76

4.10 Variation of wet unit weight with EPS at OMC

(moisture content = 39%) 78

4.11 Variation of wet unit weight with EPS at 45% moisture content 79

4.12 Variation of wet unit weight with EPS at 50% moisture content 79

4.13 Variation of wet unit weight with EPS and initial moisture content 80

4.14 Unsoaked CBR curves 82

4.15 Soaked CBR curves 83

4.16 Stress-strain curve of a composite with 3% lime 85

4.17 Stress –strain curve of a composite with 5% lime 85

4.18 Stress – strain curve of a composite with 7% lime 86

4.19 Typical shear box test on Soil-EPS composite at different

normal stress levels 87

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Figure Title Page

4.20 Vertical displacement of the Soil-EPS composite in shear box test at

different normal stress levels 87

4.21 Shear strength of Soil-EPS composite 88

5.1 Variation of plasticity index at different locations of the world 96

5.2 Particle size distribution curve for sand 97

5.3 X-ray diffraction plot of the bentonite used in the study 99

5.4 Liquid limits and plastic limits for sand bentonite mixes 100

5.5 Variation of plasticity index with bentonite content 101

5.6 Plasticity chart for the sand-bentonite mixtures 102

5.7 Expansion potential of sand-bentonite mixes as predicted by

the chart of Williams and Donaldson (1980) 103

5.8 Compaction curve for SB16 104



5.11 Variation of dry unit weight with bentonite content 106

5.12 Test method samples 108

5.13 Variation of pH for different percentages of lime at different

bentonite contents 109

5.14 Variation of optimum lime content for different plasticity indices 109

5.15 Venco pug mill used in preparing SWEPS mixes 111

5.16 Typical SWEPS mix 111

6.1 Extruded SWEPS mix specimen 116

6.2 Compaction curves for SB16 at different EPS contents 117



6.5 Variation of maximum dry unit weight of soil with different

percentages of EPS at different bentonite contents 120

6.6 Variation in maximum dry unit weight with EPS content for

different soils 120

6.7 Compaction curves of decomposed granite mixed with HCCE 124

6.8 Soil – EPS volumes (a) as a composite (b) as individual components 125

6.9 Generalised volumes of EPS in SWEPS mix at different % of EPS by

Dry unit weight of soil 126

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Figure Title Page

6.10 The relation between the PI and the measured and predicted values of dry

unit weight 128

6.11 The relation between measured and predicted dry unit weights 128

7.1 Diagrammatic representation of static compaction of oedometer

Specimen 134

7.2 Variation of free swell with time at different EPS contents for SB16 136



7.5 Time-Free swell hyperbolic relationship for SB16 139

7.6 Free swell vs. time for SB16 at 0.0% EPS content 140












7.18 Differences in free swell values between experimental and hyperbolic

approximations (a) SB16, (b) SB24 and (c) SB32 143

7.19 Variation of maximum free swell with EPS content 144

7.20 Variation of maximum free swell with bentonite content 145

7.21 Variation of free swell with clay content for 0.0% EPS 146




7.25 Relation between the PI and the measured and predicted values of

maximum free swell 147

7.26 The relation between measured and predicted maximum free swell 148

7.27 Variation of maximum swell pressure with EPS content 148

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Figure Title Page

7.28 Variation of maximum swell pressure with bentonite content 149

7.29 Relation between the PI and the measured and predicted values of

maximum free swell 150

7.30 The relation between measured and predicted maximum free swell 151

7.31 Reduction in swell pressure, free swell and dry unit weight for SB16 151



7.34 Variation of free swell with maximum dry unit weight for

different soils 153

7.35 Variation of swell pressure with maximum dry unit weight for

different soils 154

7.36 Variation of free swell and swell pressure with decrease in bentonite 154

7.37 Cyclic swelling test setup with CBR moulds 157

7.38 Variation of swell potential with increasing cycles for SB24 160

7.39 Variation of swell potential with increasing cycles for SB32 160

7.40 Variation in free swell with and without lime at various EPS contents 162

7.41 Variation of free swell with time with and without lime addition

for 0% EPS content 162

7.42 Variation of free swell with time with and without lime addition

for 0.3% EPS content 163

7.43 Variation of swell pressure with and without lime at various

EPS contents 163

7.44 Variation of axial shrinkage with bentonite content for four

different % of EPS 168

7.45 Variation of diametral shrinkage with bentonite content for

four different % of EPS 169

7.46 Variation of volumetric shrinkage with bentonite content for

four different % of EPS 169

7.47 Relation between the PI and the measured and predicted values

of volumetric shrinkage 173

7.48 The relation between measured and predicted volumetric shrinkage 174

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Figure Title Page

8.1 Direct shear apparatus used in the present study 178

8.2 Primary settlement of SWEPS mix with EPS at different normal

loads for (a) SB16, (b) SB24 and (c) SB32 181

8.3 Variation of primary settlement with bentonite content at

0.0% EPS content 182







8.7 Direct shear results for SB16 at 25 kPa normal stress, (a) Shear stress

vs. shear displacement and (b) Vertical displacement vs. shear

displacement 185



displacement. 185



displacement 186



displacement 186



displacement. 187



displacement. 187



displacement 188

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Figure Title Page



displacement 188



displacement 189

8.16 Postulated shear failure mechanism of EPS beads 190

8.17 Variation of shear stress and shear displacement with 0.3% EPS for

different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa 191





8.20 Variation of shear stress with normal stress for SB16 194



8.23 Variation of cohesion with EPS 196

8.24 Variation of angle of internal friction with EPS 197

8.25 Triaxial testing equipment 199

8.26 A set of SWEPS test specimens after being tested 201

8.27 Stress - strain curves at different EPS contents for SB16 at confining

pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 203





8.30 Stress-strain response of SB16 at different confining pressures for

EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and

(d) 0.9% EPS 206



(d) 0.9% EPS 207

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Figure Title Page



(d) 0.9% EPS 208

8.33 Variation of Initial tangent Young’s modulus with confining pressure

and EPS content for SB16 210





8.36 Composite modulus for SB16 at 25 kPa confining pressure 212

8.37 Composite modulus for SB16 at confining pressures of (a) 25 kPa

(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 213





8.40 The relation between measured and predicted initial tangent Young’s

modulus 216

8.41 s-t plots for SB16 217



8.44 Variation of cohesion (c) and angle of internal friction (φ) for

different soils (a) SB16, (b) SB24 and (c) SB32 219

8.45 Typical failure modes of SWEPS mixes 220

8.46 Variation of cohesion with EPS for different soils 221

8.47 Variation of angle internal friction with EPS for different soils 221

8.48 The relation between measured and predicted cohesion 224

8.49 The relation between measured and predicted angle of internal friction 224

8.50 Failure envelopes of (a) SB16, (b) SB24 and (c) SB32 at various

EPS contents 226

8.51 Stress - strain curves at different EPS contents for SB24 with lime at

confining pressures of (a) 50 kPa, (b) 100 kPa and (c) 200 kPa 229

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Figure Title Page

8.52 Stress-strain response of SB24 with lime as stabiliser at different

confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS,

(c) 0.6% EPS and (d) 0.9% EPS 230

8.53 s-t plots for SB24 with lime 231

8.54 Variation of cohesion with and without lime for SB24 231

8.55 Variation of angle of internal friction with and without lime for SB24 232

9.1 Specimen preparation for suction measurement 240

9.2 Contact surfaces of the two halves and the EPS content at the interface 240

9.3 PVC ring separator above the soil specimen placed in an enclosed jar 240

9.4 Variation of total suction with EPS content for three soils 241

9.5 Variation of matric suction with EPS content for three soils 242

9.6 Variation of osmotic suction with EPS content for three soils 242

9.7 Variation of total suction with bentonite content at different

EPS contents 243

9.8 Variation of matric suction with bentonite content at different

EPS contents 244

9.9 Example of desiccation cracking in compacted clay in field 249

9.10 Desiccation specimens under observation 255

9.11 Extraction of surface cracking from specimens 256

9.12 (a) Photograph of the SWEPS mix and (b) Inverted image of the

photograph in black and white 257

9.13 Variation of CIF with EPS for 86 mm diameter specimens at varying

heights of (a) 20 mm and (b) 40 mm 258

9.14 Variation of CIF with EPS for 150 mm diameter specimens at varying

heights of (a) 20 mm, (b) 35 mm and (c) 70 mm 259

9.15 Variation of CIF with EPS for 150 mm diameter specimens at

varying heights for different bentonite contents of (a) SB16,

(b) SB24 and (c) SB32 261

9.16 Variation of CIF with EPS for 86 mm diameter specimens at

varying heights for different bentonite contents of (a) SB16,

(b) SB24 and (c) SB32 262

9.17 Variation of CIF with EPS for H/D of 0.47 at different bentonite

contents of (a) SB16, (b) SB24 and (c) SB32 264

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Figure Title Page

9.18 Variation of CIF with EPS for H/D of 0.23 at different bentonite

contents of (a) SB16, (b) SB24 and (c) SB32 265

9.19 Variation of CIF with EPS content for H/D of 0.47 and 0.23

for (a) SB16, (b) SB24 and (c) SB32 266

9.20 Variation of volumetric shrinkage with CIF 267

10.1 Variation of hydraulic conductivity with EPS 272

10.2 Typical log-time plot for the first increment of loading (a) 0.0% EPS,

(b) 0.3% EPS and (c) 0.6% EPS 275

10.3 Percent decrease in height with time at 200 kPa consolidation pressure 276

10.4 Variation of mv with EPS content 277

10.5 Variation of cv with vertical effective stress at different EPS contents 277

10.6 Variation of hydraulic conductivity with EPS content 278

10.7 Schematic representation of water balance computations by HELP

program 280

10.8 Variation of average annual percolation rate with EPS content 289

11.1 Compression and elastic rebound of pre-puff EPS beads upon loading

and unloading respectively 293

11.2 Flow chart for the mix design of SWEPS mixes 295

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LIST OF TABLES Table Title Page

2.1 General uses of EPS 11

2.2 Properties of EPS 12

2.3 The first documented use of EPS as a geofoam as lightweight fill in

different countries 15

2.4 Earlier applications of Soil-EPS mixes in Japan 18

2.5 Components for Soil-EPS mixes 22

2.6 Unit weight variations 23

2.7 EPS Products manufactured in Australia (state by state) in tonnes per

annum 31

3.1 Soil factors that influence swell-shrink movements 41

3.2 Environmental factors that influence swell-shrink movements of soils 41

3.3 Comparison between behaviour of non-expansive soils and expansive

soils 42

3.4 Different types of limes 50

3.5 Free vertical swelling strains and swell pressures 55

3.6 Average three-dimensional shrinkage strains of fibre treated soils 57

3.7 Swelling pressure of natural soil and soil with polymer additives 61

4.1 Properties of marine clay at different locations of the world 67

4.2 Effect of temperature on mass and volume of EPS cubes 71

4.3 Characteristics of the dredged soil 73

4.4 Wet unit weights of Soil-EPS mixes at different mix proportions 77

4.5 CBR Values of the Soil-EPS mixes 82

4.6 Unconfined compressive strength of Soil-EPS mixes 84

4.7 Swelling and shrinkage of the Soil-EPS mixes 90

5.1 Index properties of expansive soils from different locations around the

world 95

5.2 Properties of bentonite 98

5.3 Mineralogy of Miles bentonite 98

5.4 Bentonite content and mix properties 102

5.5 Variation of hygroscopic moisture content 103

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Table Title Page

5.6 Maximum dry unit weight and optimum moisture content of SB mixes 106

5.7 Optimum lime content for SB16 mix 108



5.10 Specific gravity of the soil with and without EPS beads 112

6.1 Effect of fibre reinforcement on MDD and OMC of cohesive soils 123

7.1 Shrinkage characteristics of SB mixes 167

7.2 Reduction in volumetric shrinkage strain with the addition of EPS 172

8.1 Shear displacement at peak stress at various normal stresses 183

8.2 Variation of peak shear stress with normal stress 184

8.3 Variables in triaxial testing 201

8.4 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB16 209



8.7 Regression coefficients from failure envelopes 227

9.1 Calibration curves for Whatman No. 42 filter papers 238

9.2 Relationship between suction and shear stress for SB16 245



9.5 Variables in desiccation studies 254

10.1 Initial pressure and increments in pressure followed 274

10.2 Properties of soils used 285

10.3 Average annual totals for years 1 through 100 287

10.4 Variation of different parameters among different sites 288

10.5 Average annual totals for years 1 through 100 for Cairns 288

10.6 Average annual totals for years 1 through 100 for Perth 288

10.7 Average annual totals for years 1 through 100 for Alice Springs 289

xxvii

NOMENCLATURE

a Constant (slope of line in hyperbolic analysis of free swell)

b Constant ( intercept with y-axis in hyperbolic analysis of free swell)

c Cohesion (kPa)

Df Final diameter of specimen (m)

Di Initial diameter of specimen (m)

aε Axial shrinkage strain (%)

dε Diametral shrinkage strain (%)

fε Failure strain (%)\

es Free swell (%)

vε Volumetric shrinkage strain (%)

Eti Initial tangent Young’s modulus (kPa)

Gs Specific gravity of solids

Hf Final height of specimen (m)

Hi Initial height of specimen (m)

Ks Saturated hydraulic conductivity (m/year)

Kθ Unsaturated hydraulic conductivity (m/year)

qu Unconfined compressive strength (kPa)

t Time from the start of inundation (minutes)

Vcomp Volume of composite (expressed as 100%)

VEPS Volume of EPS (expressed as 100%)

Vf Final volume of specimen (m3)

Vi Initial volume of specimen (m3)

Vs Volume of soil (expressed as %)

Ws Dry mass of soil in the composite (kg)

1σ Peak major principal stress (kPa)

3σ Minor principal stress (kPa)

( )31 σσ − Deviator stress at failure (kPa)

dγ Dry unit weight of the composite (kN/m3)

φ Angle of internal friction (° )

xxviii

xxix

List of publications • Illuri, H. K and Nataatmadja, A. (2004), “Utilisation of dredged soil as

lightweight fill materials”, Proceedings of International Conference on Coastal Infrastructure Development- Challenges in the 21st Century, Hong Kong, 22-24 November 2004.

• Illuri, H. K. and Nataatmadja, A. (2004), “Engineering characteristics of a

soil-EPS composite”, Proceedings of 18th Australasian Conference on the Mechanics of Structures and Materials, Perth, 1-3 December, 2004, Vol. 2, pp.1013-1018, Rotterdam: Balkema.

• Illuri, H. K and Nataatmadja, A. (2007), “Shrink-swell and cracking of sand-

bentonite mixes with EPS inclusion”, 13th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (Margarita 2007), Venezuela, 16-20 July, 2007.

• Illuri, H.K. and Nataatmadja, A. (2007), “Reduction of shrink-swell potential

with EPS inclusion”, 10th Australia and New Zealand Conference on Geomechanics, 21-24 October, 2007, Brisbane (Paper accepted)

1

CHAPTER 1 - INTRODUCTION ___________________________________________________________ 1.1 Background

In recent times, the use of alternate materials that are recycled, lightweight or

both; either for construction purposes or geotechnical applications, is gaining

importance around the world. Because of the inherent engineering value of the

materials, difficulty in getting virgin materials and lack of landfill sites, low

quality or recycled materials are becoming acceptable in the construction industry.

The development of new engineering materials with controlled properties from

unconventional sources has the potential of improving the sustainability of many

engineering projects.

There are many types of waste and by-product materials with potential uses in

highway environment. Ground recycle asphalt pavement, crushed bottom ash,

blast furnace slag, shredded tyres etc. are used as highway materials in many

countries (Eighmy and Magee, 2001; Sherwood, 2001; Inyang, 2003). For landfill

constructions, many waste materials such as fly ash, domestic refuse incinerator

ash, dredged silts, waste water treatment sludges etc. have been investigated in the

past (Elshorbagy and Mohamed, 2000).

With more emphasis now being placed on engineering for sustainable

development, there is a real need to try various practical applications for waste

materials and pass the practical information to designers (Goodhue et al., 2000).

Inyang (2003) stated that the United States of America and Australia are examples

of large countries where recycling efforts are favoured. Furthermore, Inyang

(2003) also proposed the framework for feasibility assessment and project

implementation methodology for the utilisation of waste and recycled materials in

civil engineering construction.

The current research was conceived to find an alternative application for the use

of expanded polystyrene (EPS) beads recycled from produce and packaging boxes

for various geotechnical applications. Expanded polystyrene is produced from a

mixture of about 5-10% gaseous blowing agent, most commonly pentane or

carbon dioxide and 90-95% polystyrene by weight (Horvath, 1995, Scheirs,

Chapter 1

2

1998). The solid plastic is expanded into foam through the use of heat, usually

steam. This product has to be differentiated from the extruded polystyrene (XPS),

which is commonly known by the trade name Styrofoam.

EPS is generally used as a packaging medium for a variety of consumer

appliances and electronic equipment and can be custom made to the shapes of

choice very easily as shown in Figure 1.1. The main feature which makes EPS

products the primary option for transporting fragile and sensitive electronic goods

or equipment is its very low density. Moreover, it has very good thermal

insulation qualities. Due to its convenience and low cost, EPS usage is increasing

in the consumer market. That in turn results in a continuing increase in the

availability of waste EPS products. Once the primary purpose of safe

transportation of sensitive goods is over, the packaging is generally discarded into

landfills.

Figure 1.1 EPS packaging products.

Because of their lightweight and bulky nature, the waste EPS products occupy a

substantial area of the landfill (Lye et al., 2002; Shin, 2005). This in turn means

that landfills reach their capacity quickly. Unlike other organic materials, EPS is

not decomposable or biodegradable. Because of these problems, the European

Chapter 1

3

Union has restricted the disposal of EPS into landfills and set recycling targets

(PPW Directive, 2005). These impositions have forced manufacturers to look for

alternative reuse and recycle options. There are many recycling options available

like thermal and compression methods. However, possible contamination of the

products while in transportation and their limited usage make some of the

products unsuitable for recycling. Hence there is a need to try other innovative

applications for the bulk utilisation of waste EPS.

The current research was conducted to investigate the recyclability of EPS

packaging products in geotechnical applications by using recycled EPS beads as a

mechanical admixer in soils at their optimum moisture contents. The applications

of recycled EPS as a swell-shrink modifier as well as a desiccation controller of

expansive soils were considered in this study. The quantitative evaluation as to

whether recycled EPS beads provides significant benefits for use in lightweight

fills and landfill cover systems was done through an extensive experimental

program.

Expansive soil problems are experienced in many countries throughout the world.

These include U.S.A., China, France, Spain, Denmark, South Africa, Australia,

Romania, Saudi Arabia, Zimbabwe, the U.K and India (Chen, 1988). In Australia,

expansive soils are common occurrence, particularly in some regions in

Queensland, Victoria, South Australia, and Western Australia (Richards, 1990).

The annual cost of expansive soil damage was estimated to be billions of dollars

throughout the world. The damage, however, is not limited to buildings with

shallow foundations. It includes roads, services and other structures, including

commercial buildings (Nelson and Miller, 1992).

Expansive soils have a peculiar problem of swelling and shrinkage due to

moisture content variations. These swell-shrink movements cause considerable

distress to the buildings and pavements either through heave or settlement

depending on the applied stress level and the soil swelling pressure. Hence, design

and construction of civil engineering structures on and with expansive soils is a

challenging task for geotechnical engineers around the world. There are many

conventional mechanical treatments available for control of these problems. These

Chapter 1

4

include prewetting, soil replacement with compaction control, moisture control,

surcharge loading and thermal methods (Chen, 1988; Nelson and Miller, 1992).

However, these methods have their own limitations with regards to their

effectiveness and costs.

Time and again various researchers emphasised the need to find various

innovative alternatives for treating expansive soils (Chen, 1988; Nelson and

Miller, 1992; Petry and Little, 2002; Punthutaecha et al., 2006). Until now, new

methods are still being researched to reduce the swell-shrink potential of

expansive soils.

Stabilisation of expansive soils with various additives including lime, cement, fly

ash, and calcium chloride has achieved some success (Desai and Oza, 1997;

Cocka, 2001; Phanikumar et al., 2001, Punthutaecha et al., 2006). In general,

cement-stabilised soils are prone to high temperature cracking, whereas strength

gain through lime stabilisation is moderate. Furthermore, both stabilisers can be

leached out from soils by water with passing time (Puppala et al., 2003).

Moreover, with cyclic wetting and drying, the beneficial effect of lime

stabilisation is partially lost on lime treated soils because of the partial breakdown

of cementation bonds and reduction in dry unit weight and moisture content (Rao

et al., 2001). In spite of these limitations lime is commonly used as a chemical

stabiliser for expansive soils in combination with other materials like fibres.

Clays have been recognised historically as ‘ideal’ cover materials due to their low

hydraulic conductivity. However, shrinkage cracks due to desiccation can

considerably impair the long-term performance of the clay covers (Miller and

Rifai, 2004). These cracks provide pathways for the moisture migration into the

landfill covers which increase the generation of waste leachate (Albrecht, 1996;

Drumm et al., 1997).

To avoid swell-shrink in expansive soils and cracks in clayey soils, the mixing in

of fibres was analysed by Al-Wahab and El-Kedrah (1995), Zeigler et al. (1998),

Puppala and Musenda (2000), Loehr et al. (2000), Punthutaecha et al. (2006).

Fibres were used by Miller and Rifai (2004) for landfill liner materials. It was

Chapter 1

5

shown that adding fibres can reduce the swell-shrink potential of expansive soils.

Furthermore, sand-bentonite mixes have been described as good cover materials

which can minimise desiccation. However, their behaviour in cyclic wetting and

drying has not been adequately studied. The repeated swelling and shrinkage

caused by cyclic wetting and drying could be detrimental for landfill covers.

1.2 Hypothesis and focus of the research

The hypothesis of this study is that reusing EPS beads can control the swell-shrink

property of expansive soils thus enabling them to be recycled in geotechnical

applications.

The primary focus of this research was to develop, characterise and trial a new

soil stabilisation technique using recycled EPS. The soil stabilisation technique

was expected to improve the performance of soils with high plasticity by reducing

the swell-shrink potential and desiccation cracking.

The innovative application of using the waste EPS as an admixer or modifier with

expansive soil at optimum moisture content so as to make a beneficial use of the

waste EPS products is a relatively new concept. The use of waste EPS products in

crushed bead form promotes recycling and minimises the quantity of waste EPS

products reaching to the landfill considerably.

The inclusion of EPS to clay soils may offer an alternative method to chemical

stabilisation techniques and other methods for reducing swell-shrink potential.

Basically, it acts as a partial soil replacement technique whereby recycled EPS

beads are mixed with in-situ soil. By doing this the in-situ soil is actually being

reused instead of replaced.

Most of the available literature presents data on the use of pre-puff (virgin) EPS

beads mixed with dredged soil at higher moisture contents and also by adding

stabilisers. There is a lack of information about the behaviour of EPS mixed soils

at optimum moisture content of the soil. This study, therefore, seeks to fill this

gap.

Chapter 1

6

At the beginning of the research, a preliminary study was conducted with

expansive soil obtained from a port dredging activity. In this particular study the

various factors that would influence the EPS inclusion rate and unit weight

variations were analysed. Based on the findings, a detailed study was conducted

on laboratory prepared expansive soils. The reconstituted expansive soils were

made from fine sand and bentonite of various proportions to represent clays of

intermediate, high and very high plasticity indices. It has been previously

mentioned that the addition of bentonite to sand has been routinely used over the

years in developing new landfill liner or cover systems and other bentonite-

enhanced soils (Graham et al., 1989; Kenny et al., 1992; Van Ree et al., 1992;

Daniel and Wu, 1993; Pandian et al., 1995; Mollins et al., 1996; De Magistris et

al., 1998; Chapuis, 2002; Shirazi et al., 2005; Chalermyanont and Arrykul, 2005)

The physico - mechanical behaviour of sand and bentonite has been extensively

studied in the past by many researchers. The available data has been very useful in

the current study in the characterisation of the reconstituted clays.

The new method of treatment proposed in the present research is simply based on

the admixing of recycled EPS beads to expansive soils. The beads can be

randomly distributed and can control the swelling potential of expansive soils by

functioning as a swell-shrink modifier rather than improving the shear strength of

soil, which is generally done by other fibrous materials.

1.3 Objectives of the research

1.3.1 Main objective

The main objective of this study was to investigate the feasibility of using a

significant portion of waste EPS beads for beneficial purposes in civil engineering

applications through the improvement of and consequent increase in the use of

technology that is cost effective and environmentally friendly. The study was to

show the effectiveness of waste EPS beads in reducing the swell-shrink potential

of expansive soils and landfill covers; and to collect data on the comprehensive

behaviour of the soil-EPS mix with respect to shear strength, swell-shrink

potential, hydraulic conductivity, desiccation and suction properties.

Chapter 1

7

1.3.2 Specific objectives

• Prepare reconstituted soils that are potentially expansive and varying in

their plasticity index in order to get a more distinctive response when

mixed with recycled EPS beads at their optimum compaction conditions

by using sand and bentonite.

• To investigate the compaction characteristics of the mixes for lightweight

applications.

• To undertake swelling, shrinkage and desiccation control studies with the

inclusion of EPS on reconstituted expansive soils.

• To determine the strength characteristics of the soil and EPS mixes.

• To investigate the influence of waste EPS beads on the geotechnical

properties of clays.

• To develop a procedure to optimise the mix proportion with respect to the

EPS and lime contents.

1.4 Organisation of the thesis

The material contained in this thesis is presented as eleven chapters. A review of

the previous literature published on the Expanded Polystyrene, its uses in

geotechnical applications, its use in combination with dredged soil, problems with

the disposal of the waste EPS products and the research needs is presented in

Chapter 2.

The various characteristics and distribution of expansive soils in Australia and the

conventional treatment options are described in Chapter 3. The preliminary

studies conducted with a dredged soil from Port of Brisbane to assess the swell-

shrink and strength characteristics of the soil-EPS mixes at optimum moisture

content is presented in Chapter 4. In addition, this chapter also highlights the

factors that influence the miscibility of soil and EPS.

Artificially reconstituted expansive soil development and characteristics such as

Atterberg limits, compaction characteristics are described in Chapter 5.

Subsequently, the compaction characteristics of Soil with EPS (SWEPS) mixes

for the three artificially reconstituted soils termed as SB16, SB24 and SB32 are

described in Chapter 6.

Chapter 1

8

In Chapter 7, the studies on free swell, swell pressure, cyclic swelling and

shrinkage with the addition of recycled EPS beads is described. In addition, free

swell and swell pressure with lime and EPS mixes is also described. Following

this, in Chapter 8, shear parameters and their variation with the inclusion of EPS

beads conducted by using direct shear test and triaxial shear test is described.

Suction and desiccation studies are discussed in Chapter 9.

The variation of hydraulic conductivity and compressibility with the inclusion of

EPS beads is described in Chapter 10. This is followed by an analysis on the water

balance of the landfill cover systems using Visual HELP simulation model.

Finally, in Chapter 11 the application of SWEPS technique and mix design to be

followed is described. In addition, various conclusions derived from this study are

presented. This is followed by the presentation of topics for future research.

9

CHAPTER 2 - EXPANDED POLYSTYRENE AND ITS UTILISATION ___________________________________________________________

As explained in Chapter 1, this thesis is about the utilisation of waste Expanded

Polystyrene (EPS) beads as a soil modifier. This chapter presents an overview of

EPS, its physical properties and general uses in different industries for various

applications. Furthermore, the use of EPS in earth structures as geofoam and in

soil-EPS mixes as a flowable fill at higher moisture contents are also discussed.

Various environmental concerns and constraints associated with the disposal of

EPS products and the possible recycling options in civil engineering are herein

identified.

2.1 Expanded Polystyrene

Expanded polystyrene (EPS) is a polymeric (plastic) foam that in its generic

appearance is white in colour. While the use of EPS as a packaging material is

quite well-known, geotechnical specialists now recognise EPS as the most

commonly used geofoam material, a type of cellular geosynthetic which has been

in consistent use in geotechnical applications since the early 1960s. There are

different types of plastic foams which are interchangeably referred to as geofoam.

They include expanded polystyrene (which is most frequently used), extruded

polystyrene, pre-formed sheets of polyethylene and foamed-in-place polyurethane

(Horvath, 1995). The ensuing discussion deals with expanded polystyrene (EPS)

geofoam.

2.1.1 Manufacture of EPS

The building block or monomer of EPS is styrene. Suspension polymerization of

the liquid styrene monomer is carried out in the presence of 5% - 8% (weight) of

isomeric pentanes or butanes as a blowing agent to produce solid beads of

polystyrene with an average molecular weight of between 160,000 and 260,000

(Thomson, 1995; Thompsett, 1995; Scheirs, 1998). Each resin bead contains

microscopic bubbles of pentane as the blowing agent. Beads range from 0.2 to 3

mm in diameter (medium to coarse sand sized) but are typically toward the

smaller end of the range. The beads may also contain a fire-retardant additive.

Chapter 2

10

EPS blocks or products are manufactured in a two-stage process of pre-expansion

followed by moulding. The pre-expansion stage consists of placing the beads

within a container and heating them with steam to between 80° and 110° C.

Heating softens the polystyrene and vaporises the pentane. Expansion of the

pentane within the polystyrene produces individual spheres, each approximately

50 times larger in volume than the original bead, with each sphere containing

numerous closed, gas-filled cells, called pre-puffs (Negussey, 1998).

The pre-puff, an amorphous thermoplastic in nature, is placed in an enclosed,

fixed wall mould, and the spheres are simultaneously re-softened and expanded

further using steam via holes in the walls of the mould. In modern moulding

equipment, this is done under a partial vacuum. As a result, a block or product is

formed consisting of numerous particles, each polyhedral in shape as a result of

the original expanded spheres being forced to fuse together during the additional

expansion that occurs during the moulding stage, with small or no voids between

polyhedra.

Each polyhedron retains the numerous closed cells of the original expanded

sphere from which it evolved. No adhesive is used to join the polyhedra as they

are fused during moulding. This structure of individual polyhedra provides a way

to visually differentiate EPS from other foams that have a homogeneous cellular

structure, although the extent to which each polyhedron is visible in EPS depends

to a significant degree on the size of the beads used initially (Horvath, 1995).

After release from the mould, a block or products are allowed to ‘season’,

typically for several days. The reason is that some dimensional change, usually

shrinkage (but swelling in some cases) may occur after moulding at a rate that

decreases rapidly with time. This dimensional change is a result of cooling and

final out gassing of the pentane, blowing agent, from within the cells. In most

cases, trimming is required after seasoning to produce a block that meets specified

dimensional tolerances. This trimming is done using a special machine equipped

with heated metal wires. Typically EPS blocks are manufactured with dimensions

of 305 to 1219 mm wide, 1219 to 4877 mm long, and 9.5 to 610 mm thick and are

Chapter 2

11

normally white in colour (Negussey, 1998). EPS products can easily be custom

made to the shapes of choice depending on the requirements.

The final moulded products or blocks are air-filled foams and usually range from

0.008 to 0.04 t/m3 in density (Thompsett et al., 1995). Scrap produced from

trimming and cutting a block within the moulding plant is usually recycled by

grinding it into small pieces and blending it with pre-puff to produce new blocks.

This recycled material called ‘regrind’ in the industry, typically represents 10 -

15% of the total material in a block (Horvath, 1995). The use of regrind is

separate from using ‘post-consumer’ recycled material. A comprehensive review

on the various stages of EPS manufacturing process can be found in Cook (1983)

and Horvath (1995).

2.2 General uses and properties of EPS

EPS has a very low thermal conductivity and nearly 98% of the volume is air (Lye

et al., 2002). EPS thus has many exceptional properties such as being lightweight,

thermal insulating, shock-absorbing and having low-water pick-up, etc. Around

the world, many industries use EPS products because it is clean, comparatively

inexpensive, moderately strong and resistant to air and moisture infiltration. It has

good dimensional stability and available as sheet or moulded form (Scheirs, 1998;

Shin, 2005). In addition, it does not use CFC or HCFC as a blowing agent

(Horvath, 1995). EPS in its various forms is employed, almost equally in the

production of both durable and disposable (single use) goods. Table 2.1

summarises the availability of EPS in different physical shapes and their

commercial uses.

Table 2.1 General uses of EPS (PACIA, 2002).

Type Uses

Block type Building and panel applications

Produce boxes Transport of fruits, vegetables and seafood

Waffle pods Under concrete slabs to stabilise concrete

Moulded type Packaging, helmets, cups and car seats etc

Foam cuts Using hot wire for packaging and ornamental applications

Chapter 2

12

Table 2.2 (Thompsett et al., 1995) presents the nominal properties of a typical

EPS product. EPS foam is thermoplastic and exhibits visco-elastic behaviour

under load. Its specific gravity is 0.02. In practice, the actual properties will

depend to some extent on the manufacturer of the blocks or products and these

properties may be achieved by EPS of other densities due to advances in

technology (AS 1366.3, 1992)

Table 2.2 Properties of EPS (after Thompsett et al., 1995).

Density (kg/m3) 15 20 25 30 35

Tensile strength (kPa) 200 280 350 425 500

Bending strength (kPa) 190 270 350 450 550

Linear expansion coefficient (10-5 m/mK)

7 7 7 7 7

Lowest service temperature (° C) -110 -110 -110 -110 -110

Highest service temperature (° C) +70 +70 +70 +70 +70

Grade SD HD EHD UHD -

2.2.1 Chemical resistance

Expanded polystyrene is resistant to common inorganic acids and alkalis

(including de-icing salts). There is also no evidence for any form of biological

attack on EPS. However, it is not resistant to organic solvents including petrol and

diesel oil. It is necessary to protect EPS from these substances during construction

and against the possibility of large-scale accidental spillage (Thompsett et al.,

1995). UV radiation causes superficial yellowing and friability thus having a

slight effect on the appearance of moulded polystyrene. However, it does not

otherwise affect the physical properties of the bulk material (Cook, 1983;

Thompsett et al., 1995).

2.2.2 Temperature and fire resistance

As a thermoplastic material, EPS does not exhibit a true melting point. It will

begin to soften at around 93° C, and as more heat is applied it will start flowing

away from the flame at around 120° C, rather than burning away. Flame retardant

additives (Type A) are available for control of fires (Thompsett et al., 1995) but

Chapter 2

13

these are not used in most EPS packaging products. For use in civil engineering

structures however, EPS materials should be covered with soil to eliminate the

fire risk.

2.3 Applications of EPS in Geotechnical Engineering

2.3.1 Thermal insulation

This application is based on the high percentage of air content (98%) of EPS

geofoam and constitutes the classic geofoam function since the 1960s. They have

been incorporated as frost blankets into road pavement to assist in prevention of

differential icing of road acting as a thermal insulator for highway, railroads and

airport runways to avoid deeply penetrating ground frosts (Hanna, 1978; Esch,

1995; Hillmann, 1996; Beinbrech, 1996).

2.3.2 Lightweight fill

This application is based on the very low density and high strength-to-density

ratio of EPS geofoam and has been used routinely since 1970s for replacing the

soil sub-grade of pavements, railway track systems and embankments that have

low bearing capabilities.

In 1972, the Norwegian Road Research Organization (NRRL) used EPS blocks as

an ultra-lightweight fill on NR 159 road at Flom, near Oslo to minimise the

effects of subsidence as a result of marshy soft ground. The road was built over a

peat bog where the in-situ soil consists of 3 m thick layer of peat above 10 m of

soft marine clay. The settlement rate due to the weight of the road construction in

the previous years was of the order of 100 mm a year and reached 300 mm in

1972-73, accumulating to a total road surface drop of 600 mm below bridge level.

An EPS layer of 1100 mm thick was laid by excavating the same portion of soil

and further increasing the road level by providing a 500 mm thick pavement on

the top the EPS layers. During the following 12 years the subsidence was 80 mm

and then virtually no settlement occurred (Refsdal, 1985). This is the first

application of the EPS geofoam as lightweight fill over soft ground and ever since

its use has increased in all parts of the world.

Chapter 2

14

The generalised diagram (Figure 2.1) illustrates the application of EPS as a

lightweight fill on soft ground (EDO, 2003). The weight of the road embankment

is reduced because of the use of lightweight EPS geofoam, to the extent that the

self-loading imposes negligible stress on the subsoil foundation (Zou, 2001). The

first documented use of the EPS geofoam as a lightweight fill around the world in

different countries was reported in the literature and a list of them is presented in

Table 2.3. Figure 2.2 shows the EPS being placed over soft ground.

One possible limitation of using EPS geofoam as lightweight fill is the buoyancy

forces. Due to its very low density, ground water fluctuations will influence the

geofoam causing it to easily float away if not properly secured with suitable

surcharge or ground anchors by considering the maximum water levels in the area

in calculations (Horvath, 1995; Frydenlund and Aaboe, 1996). Figure 2.3 shows

the placement of EPS blocks as lightweight fill.

Figure 2.1 Generalised diagram for EPS geofoam embankment (EPS Development Organisation, 2003).

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This figure is not available online. Please consult the hardcopy thesis available from the QUT Library

Chapter 2

15

Figure 2.2 EPS being placed over soft ground (http://geofoam.syr.edu/GRC_issa.asp).

Table 2.3 The first documented use of EPS as a geofoam as lightweight fill in different countries.

Year Country References

1972 Norway Frydenlund and Aaboe, 1996

1983 France Magnan and Serrate, 1989

1984 Netherlands Dorp, 1996

1985 U K Williams and Snowdon, 1990

1985 Germany BASF, 1998

1985 Japan Gosaburo, 1996

1985 Australia McDonald and Brown, 1993

1987 USA Preber et al., 1994

Figure 2.3 Placement of lightweight fill (http://geofoam.syr.edu/GRC_issa.asp).

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Chapter 2

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2.3.3 Compression inclusion

This application first appeared in the 1980s and utilizes the high compressibility

of EPS geofoam (Horvath, 1996). The EPS, when in contact with soil, deforms

and allows full mobilisation of the soil shear strength, thus, reducing the stress

transmitted to relatively stiff (or rigid) structures like retaining walls or slabs.

2.3.4 Vibration damper

This application, whose potential is under investigation to utilise the energy

absorbing capabilities of EPS geofoam in a sense that the geofoam can act as a

cushion beneath a pavement or railway track thereby reducing the airborne

vibration (sound) as well as ground borne vibrations (Horvath, 1995; Siderius,

1998).

2.3.5 Other applications

Other geotechnical applications such as thermal insulation above clay liners in

landfills and waste-containment facilities, or adjacent to below-ground walls can

be performed by using thinner sections of geofoam. In these applications,

geofoam panels of 25 - 100 mm thick are usually needed. It is also possible to cut

a block into intricate shapes by using hot-wire to be used as a casting form for

architectural and ornamental purposes (Horvath, 1994). Another EPS product

employing pre-puff (see Section 2.1.1) was developed specifically for the landfill

applications to avoid problems due to freeze and thaw (Benson et al., 1995).

EPS is also used in lightweight concrete owing to its lightweight, excellent heat

preservation and sound insulation properties (Ravindrarajah and Tuck, 1994;

Miled et al., 2004; Babu et al., 2005). Waste EPS granules have been used in with

horticultural soils to improve a number of soil characteristics like improving

drainage, lightening heavy soils and improving water uptake capacity of soils

(Scheirs, 1998). Furthermore, it was also used as sub-base materials for

pavements and railway track beds (Hanna, 1978; Duskov, 1996; Miki, 1996;

Beinbrech, 1996; Siderius, 1998), construction materials for floating marine

structures and fenders in offshore oil platforms (Bagon and Frondistous-Yannas,

1976), sea beds and sea fences; as an energy absorbing material for buried

Chapter 2

17

military structures, (Cook, 1983; Perry et al., 1991) and tunnel covering

(Beinbrech, 1996).

2.4 Soil-EPS mixes as lightweight fill materials

The use of EPS beads in soil to produce lightweight fill materials is a new

concept. There are relatively few publications available on this topic. However, a

number of Japanese researchers, particularly those of the largest civil engineering

research institutes in Japan (Public Works Research Institute or PWRI in Tsukuba

and Port and Harbour Research Institute), have been working in this area since

1992. The following is a concise review of the techniques adopted by different

Japanese researchers.

In Japan, 45% of dredged soil, 21% of surplus soil from projects sites in the cities

and 8% of industrial waste are stored in the bulkheads every year (Okumura,

2000). As the availability of land for suitable disposal sites has become scarce, the

need to recycle the waste soil has arisen. In 1992, a research consortium

consisting of Port and Harbour Research Institute, Coastal Development Institute

of Technology and 23 research institutes affiliated with construction companies

was formed to develop a new fill material known as Super Geo Material (SGM)

using dredged and surplus soils (Tsuchida et al., 2001).

The lightweight fill material, obtained by mixing pre-puff EPS beads with waste

soils, was one of the research outcomes of the consortium. Where higher strength

was required, stabilising materials such as cement or fibre were used. The latter

was added to enhance the resistance to erosion. The manufactured material,

containing 60000 cubic metres of surplus construction soil was used in over 70

sites (Mori, 2003).

2.4.1 Features of Soil-EPS mixes

Miki (1996) explained that because of the inclusion of EPS beads, soil-EPS mix

is lighter than ordinary soil and thus can reduce the load applied to the ground.

Furthermore, it is nearly as flexible as ordinary soil and can cope with ground

subsidence. In addition, the strength can be adjusted to the requirements by the

Chapter 2

18

addition of a stabiliser appropriate to the soil type and compaction can be done as

with ordinary soil. This technique is suitable to all but gravelly soils (Mori, 2003).

2.4.2 Earlier applications

During this study, from the literature, it was observed that the new material (soil-

EPS mixes) had been used in a number of ports, harbours and other public

facilities in huge quantities (Table 2.4).

Table 2.4 Earlier applications of Soil – EPS mixes in Japan.

Project Quantity placed (m3)

Special features

Quay wall (10 m) in Port of Fushiki-Toyama1

900 First application in Japan

Quay wall (-7.5 m) in Port island, Port of Kobe1

21,610 First large-scale application in Japan. Use of dredged soil

Seawall and ground improvement in Tokyo international airport1

84,610 Use of sandy soil

Quay wall in Ishikari Bay New Port1 7,110 Use of mixture of soil on site and bentonite. Winter application in cold region

Ground improvement in Oi wharf, port of Tokyo1

11,200 Submerged application at –10m.

Quay wall (-7.5 m) in port of Yokohama1

70,000

Use of dredged organic soil Use of protein active agent

Hiroshima city, construction of high-tide river dike on soft ground2

1,500 To reduce settlement and to control lateral flow

Banking on a road in a landslide zone in Higashi-tagawagun2

1,800 To reduce loads and to provide a countermeasure against landslides

Banking on rear of embankment at Hachiohe city2

2,500 To reduce earth pressure and loads.

1 Okumura, 2000; 2 Miki, 1996

2.4.3 Construction processes

There are two construction processes for soil-EPS mixes which differ in the

machinery used and also in the mix compositions (Figures 2.4, 2.5 and 2.6).

Chapter 2

19

2.4.3.1 Construction process for dredged soil

Mud dredged from the seabed is collected in a floating barge. Large objects are

removed by a vibrating sieve installed on the agitation tank. Seawater is added

and regular measurements are performed to adjust the water content and density to

the desired level by �-ray density sensor and the prepared slurry is then supplied

to the mixing plant by sand pump. The pre-puff EPS beads and binder (Portland

cement) are subsequently mixed to control the density and strength of the

composite. If airfoam is used as lightweight material, a foaming machine is used

for mixing it with soil. Airfoam is generated from foaming agents prepared from

animal protein foaming material with a density of 0.031 t/m3 and compressed air

(Hayashi et al., 1998). The soil-EPS mix is placed in forms using a tremie pipe

(Tsuchida et al., 2001).

Figure 2.4 Construction process for port and harbour structures

(Satoh et al., 2001).

2.4.3.2 Construction process for surplus construction soil

Onsite mix method

In the onsite mixing process (Figure 2.5a), the pre-puff EPS beads and stabilising

agents (Portland cement or hydrated lime) are spread on the ground in uniform

thickness, and then, by using an excavator equipped with a special mixing blade

as shown Figure 2.5b, these additives are thoroughly mixed with the soil by

adding water in the required quantities. Finally, compaction is carried out by

levelling and rolling to the desired degree.

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Chapter 2

20

a. Mixing of EPS beads and stabiliser.

b. Mixing machine.

Figure 2.5 On-site mixing process (Miki, 1996).

Plant mix method

In the plant mix method (Figure 2.6), excess construction soil is transported to the

central mixing plant by trucks in which the pre-puff EPS beads and stabilising

agent suitable for the soil type are added along with water, and the resulting mix is

transported to the site where the levelling and compaction by rolling is carried out.

This method was reported to be more effective than on-site mixing process (Miki,

1996).

2.4.4 Mix proportion

As this technique is still in its infancy, there is no consistent mix proportion

adopted for all the cases. The mix proportions adopted by different researchers

and the corresponding wet densities obtained and the target compressive strength

are shown in Table 2.5.

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a. Plant mix method.

b. Sealed batch type mixing plant.

Figure 2.6 Central mixing plant (Miki, 1996).

It is interesting to note that Satoh et al. (2001) and Tsuchida et al. (2001) added

water to the dredged bay mud (initial moisture content = 84%) to reach a moisture

level of 2.5 times the liquid limit (i.e. slurry form) to reduce its density. Miki

(1996) used the same technique but did not comment on the initial water content

of the soil and the rationale behind the subsequent addition of the water. In all of

the above mixes, the aim was to reach the target unconfined compressive strength

(UCS) after 28 days, after mixing. However, it is to be noted that the UCS is

obviously influenced by the moulding moisture content of the soil.

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Table 2.5 Components for Soil-EPS mixes.

Soil (kg)

EPS Beads

(l)

Stabiliser (kg)

Water (l)

Wet Density (t/m3)

UCS (kPa)

Ariake clay 1 (dry)

367 to 375

215 to 224

80 to 100

(Cement)

625 to 638

1.2 200

Tokyo bay mud2 (dry)

789 161 100 (Cement)

261 1.2 559

Tokyo bay mud2 (under water)

714 206 200 (Cement)

236 1.2 1601

Sandy soil3 (� = 1.8 t/m3)

900 850 40 (Cement)

50 1.0 98

Sandy soil3 (� = 1.8 t/m3)

1120 630 30 (Cement)

40 1.2 98

Cohesive soil3 (� = 1.6 t/m3)

950 650 40 (Lime)

0 1.0 98

Cohesive soil3 (� = 1.6 t/m3)

1140 470 50 (Lime)

0 1.2 98

Cohesive soil with high water content3 (� = 1.6 t/m3)

940 530 50 (Lime)

0 1.0 98

Cohesive soil with high water content3 (� = 1.6 t/m3)

1140 330 50 (Lime)

0 1.2 98

1Satoh et al., 2001; 2Tsuchida et al., 2001; 3Miki, 1996

2.4.5 Properties

2.4.5.1 Wet unit weight: The wet unit weight of the soil-EPS mix can be set in

the range of 6 kN/m3 to 20 kN/m3 depending upon the mix proportion of the soil,

pre-puff EPS beads and the hardening agent such as lime or cement as shown in

Figure 2.7 (Miki, 1996).

For under seawater placement at Kumamoto port, Satoh et al. (2001) poured soil

mixed with EPS beads inside concrete caissons (Figure 2.8). and studied two

cases. The soil-EPS mix was placed at 4.7 m deep in two separate chambers (Case

3 and Case 5) by varying the cement content between 80 kg/m3 and 100 kg/m3.

The variation in unit weight after mixing is presented in Table 2.6.

Chapter 2

23

Clays

Sandy soil

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3

Mixture ratio of expanded beads to soil, %

Wet

un

it w

eig

ht,

kN

/m3

Figure 2.7 Relationship between wet unit weight and mixture ratio of EPS beads

(after Miki, 1996).

Figure 2.8 Sections of caissons and testing cases (Satoh et al., 2001).

Table 2.6 Unit weight variations (Satoh et al., 2001).

The dredged clay was diluted to a water content of about 170% (2.6 times liquid

limit) so as to reduce the unit weight of the dredged clay from 16.2 kN/m3 to 13.0

kN/m3 (slurry). Another layer of foam treated soil of 5.2 m was placed above the

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This table is not available online. Please consult the hardcopy thesis available from the QUT Library

Chapter 2

24

soil-EPS mix. The variation of the wet unit weight immediately after mixing for

each case is shown in Figure 2.9. In the same figure, the measured range of the

wet unit weight of the lightweight treated soil just after being transported to the

site is also shown. It can be seen that in all the cases, the wet unit weights after

transportation were larger than the wet unit weight immediately after mixing.

Satoh at al. (2001) attributed this to the pressure in the transportation pipe and the

separation and loss of EPS beads during placing. The maximum compression in

the transportation pipe was 100 ~ 150 kPa, which might have caused the

irrecoverable compression of EPS beads. Furthermore, it was also observed that

during the underwater placement some of the EPS beads were separated and

drifted to the water surface, this volume was about 2% to 3% of the total beads

mixed. The change in the wet unit weight after one year is shown in the Figure

2.10. It is seen that the unit weight marginally increased after one year for the

same composite.

Figure 2.9 Wet unit weight of soil-EPS mix immediately after placing

(Satoh et al., 2001). In another study, Minegashi et al. (2002) studied the relationship between the

percentage of EPS beads and the wet unit weight of the soil-EPS mix. The trend is

shown in Figure 2.11. Note that in order to achieve sufficient homogeneity; the

moisture content of the composite was kept at 120%, which was 25.3% above the

optimum moisture content.

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By comparing Figures 2.7 and 2.11, it can be concluded that the unit weight of the

composite is generally influenced by the bead content due to the lightweight of

EPS beads. These studies were performed at moisture content well above their

optimum moisture content. However, what limits the addition of EPS at around

optimum moisture content is not known. This factors needs to be assessed.

Figure 2.10 Change in wet unit weight after one year (after Satoh et al., 2001).

Moisture Content = 120%

0

1

2

3

4

8 9 10 11 12 13 14 15Apparent density, kN/m3

Per

cent

age

of E

PS

bea

ds, %

Figure 2.11 Change in apparent unit weight with mixing rate of beads

(after Minegashi, 2002).

Chapter 2

26

2.4.5.2 Unconfined compressive strength

Figure 2.12 shows the relationship between wet density and unconfined

compressive strength of a soil with and without EPS beads (after Miki, 1996).

Figure 2.12 Relationship between the wet density and UCS (after Miki, 1996).

As can be observed from the figure, the strength gain in EPS beads mixed soil

may only be achieved by the addition of stabiliser contents. Without stabiliser the

UCS varies between 50 to 200 kPa, whereas the UCS can be increased to about

1000 kPa with increase in stabiliser content. It should be noted that the addition of

stabiliser and the corresponding strength gain is influenced by the initial water

content of the soil (Bell, 1996). It is not known whether the strength gain in the

Figure 2.12 was obtained at the same moisture content.

The unconfined compressive strength of a dredged soil mixed with EPS beads and

cast underwater is shown in Figure 2.13 (Satoh et al., 2001). The specimens were

obtained by core cutting. It was found that the unconfined compressive strength

was much larger than the target value, i.e. 200 kPa. In addition, the UCS is almost

independent of the water depth and the type of the lightweight materials, but was

strongly controlled by the cement content.

Chapter 2

27

Figure 2.13 Variation of UCS with depth (Satoh et al., 2001).

The relationship between the modulus of deformation or secant modulus, E50 (in

kPa), and unconfined compressive strength, qu (in kPa), was expressed by Satoh et

al. (2001) as E50 = (189 to 359)qu. However, this is significantly larger than the

values reported by Tsuchida et al. (1996), E50 = (100 to 200)qu.

2.4.5.3 Stress-strain behaviour

Figure 2.14 shows the stress-strain curve from an unconsolidated undrained (UU)

test for a dredged soil at moisture contents of 2.5 times the liquid limit at different

confining pressures (Tsuchida et al., 1996). It can be seen from Figures 2.15 and

2.16 that the stress-strain behaviour of soil-EPS mix is influenced by the soil type

and cement content (Pradhan et al., 1993; Minegashi et al., 2002). As can be seen

from the Figure 2.15 for soft clay, no peak strength were observed where as in

Figure 2.16 for sand, different peak strengths were observed for different

confining pressures from drained triaxial compression tests. In the former, the

moisture content of the mix was 25% above the optimum moisture content

(OMC), while the latter had a moisture content of 10% above the OMC.

Furthermore, Pradhan et al. (1993) observed that the increase in cement content

increased the compressive strength. This was predominant at higher densities, i.e.

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with less EPS bead content. A similar trend was observed with the change in

stiffness, at higher cement contents the material became stiffer and brittle. Cement

is thus an important ingredient for the strength gain in the composite and

facilitates bonding of the beads and soils.

Figure 2.14 Stress-strain curves for a dredged soil mixed with EPS beads at a

moisture content of 2.5 times liquid limit (Tsuchida et al., 1996).

Furthermore, Minegashi et al. (2002) observed that a softening of stress-strain

relation of the composite under repetitive loadings continued with the increase in

the dynamic stress ratio, and decreased with the increase in the confining pressure.

In addition, it was found that the cement additive contributed to the increase in

cohesion but not to the angle of shear resistance, and the beads may not contribute

to the frictional resistance.

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Figure 2.15 Stress-strain curves for the Ariake bay mud at liquid limit

(Minegashi et al., 2002).

Figure 2.16 Stress- strain curves for the sand mixed with EPS beads with moisture

content 10% above the optimum moisture content (after Pradhan et al., 1993).

Oh et al. (2002) mixed recycled EPS beads with weathered granite soil and

studied the bearing capacity of the layers. The first layer was a soft soil and it was

overlain with granite soil with EPS inclusion. It was observed that the ultimate

bearing capacity increased with the height of the upper lightweight materials. In

addition, the ultimate bearing capacity decreased with the increase in EPS content.

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Yoonz et al. (2004) investigated the mechanical characteristics of a dredged soil

mixed with EPS beads and cement. The moisture content of dredged soil was

135% which was 3 times its liquid limit. Two percent EPS beads were added to

the mix with 35 times the foaming effect. The cement ratio was 2%. The dredged

soil had a liquid limit of 45%, plasticity index of 25% and passing 200 number

sieve was 95%. The soil was classified as clay with low plasticity (CL). They

observed that with initial water contents and EPS ratios ranging from 165-175%

and 3-4%, respectively, the mixes could achieve a compressive strength exceeding

200 kPa. Furthermore, the ultimate triaxial compressive strength of the soil did

not increase when the cement ratio was above 2%. However, they observed that if

the curing pressure of above 200 kPa was applied, the ultimate compressive

strength could increase further.

2.5 EPS applications in Australia

2.5.1 Lightweight fill

In Australia, VicRoads has been using lightweight expanded polystyrene foam

blocks for general road works since 1985, on projects such as bridge approach

embankments and lightweight embankments over soft soils. The organisation has

also developed a new technique, which has become known as the “EPS

embankments repair” (Brown, 2000). They found that the use of geofoam to

minimise the sub-soil stress was cost effective and had allowed construction

programs to proceed without delays of the kind normally associated with ground

treatment and pre-consolidation.

2.5.2 Packaging products

While EPS is a good packaging medium for transporting fragile and expensive

items, the majority of the packaging materials manufactured in Australia are used

for transporting fruit, vegetables and seafood (Table 2.7). The use of EPS for this

purpose is extensive in both the domestic and export markets (Fisher, 2000).

In an Australia-wide plastics recycling survey for the year 2004 conducted by

Plastics and Chemicals Industries Association (PACIA, 2005), it was observed

that nearly 36,000 tonnes of expanded polystyrene were consumed in Australia in

Chapter 2

31

2004. Of this, domestic reprocessing was 1600 tonnes and export for reprocessing

was 907 tonnes, which means a total recycling rate of 7.1%.

There are 17 reprocessing sites for EPS products in Australia. Most non-

packaging applications such as building and panel applications as shown earlier in

Table 2.1 would have longer application and take a longer time to reach for

recycling. The utilisation of EPS in single-use or short term packaging

applications is 35% and for long-term durable applications it is 65%. The recycled

EPS is used as waffle pods in building and wall panels.

About 39% of the produce boxes are collected by the EPS recycling group at the

collection centres, located at different mainland cities in Australia for possible

recycling (PACIA, 2005). At these collection centres, the waste EPS is placed in a

large granulation machine where it is broken up and fed into a large bag above the

compaction machine. These granulates are then compressed into pallets of

approximately 120 mm wide and forced out of the machine into suitable lengths.

These ingots are used as a general purpose plastic for manufacturing of toys,

cassette casings, coat hangers, synthetic timber etc.

Table 2.7 EPS Products manufactured in Australia (state by state) in tonnes per annum (PACIA, 2002a).

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2.6 Management of waste EPS

As described in the previous sections, EPS is undoubtedly a very versatile

material that has found useful applications in general public as well as in civil

engineering and geotechnical engineering in particular. With the ever increasing

demand for consumer goods, the use of EPS as a packaging material is growing

rapidly owing to its lightweight and exceptional insulation qualities. This

significant increase in the use of EPS has led to a growing public concern over its

impact on the environment and the dwindling landfill space (Lye et al., 2002;

Shin, 2005). This is because EPS being non-biodegradable, light in weight and

having a low mass-to-volume ratio, takes up a significant amount of space in

already overcrowded landfills.

Once its use as packaging materials ends, EPS is sent to the disposal or recycling

centres. Unlike other waste materials, whose disposal raises concerns about

possible contamination of soil or ground water because of leachability, concerns

about EPS disposal relate to the volume occupied and its non-biodegradability.

Because EPS can not be decomposed in nature, waste EPS has caused serious

environmental problems, including ocean pollution. According to one estimate

(Ikada, 1990), in 1988, 25% of total floating debris in the North Pacific Ocean

was waste EPS. In Europe, the originating manufacturer is now responsible for

the collection, recycling or disposal of waste EPS products (PPW Directive,

2005).

According to Schiers (1998), the cost of land-filling waste EPS can be between

$500 and $2500 per tonne. Added to this are the high transportation costs

associated with shipping low bulk density waste EPS. Furthermore, any attempt to

recycle EPS products would involve various technological challenges mainly

because of the low mass-to-volume ratio of the material which is a barrier to the

collection for recycling (PACIA, 2005). In light of the high cost of disposal and

growing consumer awareness of land filling and impositions from the

governments, the manufacturers have been forced to devise alternative reuse and

recycling strategies for EPS disposal.

Chapter 2

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2.6.1 EPS recycling methods

Various techniques are available for recycling EPS waste products:

(i) Material Recycling: In this method, EPS products sorted and segregated from

the solid waste stream are reduced in volume by densification or compaction of

the foam by means of hot air, IR lamps, friction, heated rotary drum etc. such that

polystyrene can be recovered as an ingot or pellet, or reused into raw material,

daily products, construction materials etc. (Noguchi et al., 1998; Scheirs, 1998;

PACIA, 2005). Densification of EPS involves the complete or partial collapse of

the cell structure because of the expulsion of air from cell. A critical issue in the

densification of EPS is the degradation of the polymer and the associated property

deterioration (Scheirs, 1998).

(ii) Chemical Recycling: In chemical recycling methods, the main idea is to

recover the styrene monomer which can be reused as a chemical resource. This is

achieved by dissolving the EPS in d-limonene – a biodegradable solvent derived

from the rinds of citrus fruits (Noguchi et al., 1998).

(iii) Thermal Recycling: Thermal recycling of EPS waste products involves their

incineration to recover the energy from its burning. However, since EPS has a

poor energy density per volume because it contains so much air, the transportation

of the required bulk volume becomes uneconomical.

2.6.2 Constraints and challenges in EPS recycling

The recycling processes described above can be labour intensive and expensive.

Furthermore, the processes can ruin the properties of EPS and demand high

energy requirements for conversion (Fisher, 2000; Shin and Chase, 2005). Hence,

in spite of the recycling techniques mentioned above, EPS usually ends up in

landfills or is incinerated, due to the following reasons (Reneker and Chun, 1996;

Lye et al., 2002; Shin, 2005).

• Places like wholesale markets, supermarkets, department stores, restaurants,

electrical appliance stores and factories generate large volumes of EPS

packaging products in their daily operations. However, in most cases, efficient

Chapter 2

34

collection of the waste EPS products from consumers, either as voluntary

drop-off or as buy-back, for recycling is minimal or sometimes absent. In

addition, unlike aluminium cans, PET bottles etc., household EPS packaging

represents a small portion of the residential solid waste stream, hence

community based recycling programs generally do not add EPS to their list of

material for collection since such quantities hardly justify the associated

transportation costs and subsequent mechanical recycling expenses (AFPR,

2001).

• Furthermore, during loading, transportation, and unloading of goods, the EPS

packaging might be damaged, making its re-use as packaging not a good

option. Additionally, to transport it back to the manufacturing unit is not cost

effective because of the low mass-to-volume ratio and the manufacturing units

are located in different states/countries.

• In addition, the cost difference between using recycled and pre-puff EPS

materials is not significant. The cost to process the recycled materials far

outweighs any returns from the sale of the materials (Fisher, 2000). And since

there is no uniform rate applied to the disposal of wastes at municipal

landfills, it is difficult to set prices at industry collection centres.

• Recycled EPS products tend to have more inferior properties than their pre-

puff (virgin) counterparts, thereby reducing their demand (Lye et al., 2002).

This is because recycling process requires post-consumer plastic materials to

be melted and remoulded through an extrusion heat cycle, which affects the

chemical and physical structure of the EPS. For example, the expansion

characteristics of recycled EPS differ from that of the natural bead of virgin

foam (Hornberger, et al., 2000). Furthermore, the bead fusion between the

new and recycled materials is not good because the recycled EPS beads

usually contain minimum or no pentane gas in them, which hinders the

effectiveness in expansion and subsequent fusion with the pre-puff in the

mould. It primarily serves as a “dead” filler material only. The damage due to

grinding or heating and the inability to expand results in void spaces in

manufactured product, which may weaken the product. To improve the

Chapter 2

35

density, recycled EPS beads need to undergo a specific treatment through a

densifier, pretreating them again with pentene gas, which would result in an

increase in the production cost for the recycled EPS beads.

• Finally, the application areas where EPS is employed are dictated by the

nature of the process. Presently, steam-injection, extrusion or palletisations are

the key processes that make use of the recycled materials for mass

manufacture of EPS products. Such processes are not suitable and cost-

effective in the handling of one-off or small batch prototyping and moulding

(Lye et al., 2002).

In reusing post-consumer recycled material for the manufacture of EPS geofoam,

Horvath (1995) mentioned the technical difficulty of commingling of EPS made

from regular and modified (flame-retardant) expandable polystyrene as they are

visually indistinguishable. This would affect the flammability of the final product

of EPS used in cushion packaging. Furthermore, Horvath (1995) states that

because of the problems associated with both mechanical properties and

flammability, there has been no regular large-scale production of EPS block

geofoam that uses a significant percentage of recycled EPS at least in USA.

Manufacturers of EPS products expressed concerns for recycling of the waste EPS

products back into the production cycle on the following technical grounds

(AFPR, 2001)

1. It is difficult for the consumer to distinguish EPS foam from polyethylene

foam, which is often a contaminant in the EPS brought to the reprocessing

centre because the properties of both materials significantly different.

2. It is difficult to remove dirt and grease from EPS foam. Consequently,

much of the waste EPS foam (foam plates and foam packaging) is not

currently processed.

3. Even though EPS is moisture resistant, foamed material absorbs some

water (1% to 5%) when washed or stored in open containers. This

increases the density of the EPS material making it more difficult to

weigh, sort and handle.

Chapter 2

36

4. Some EPS materials contain additives or co-polymers such as flame-

retardants, lubricants, antioxidants etc. When these materials are mixed

with foam packaging and other waste that do not contain flame-retardants,

the result is a material that has different flow behaviour and property.

Flame retardant material is therefore considered to be a contaminant in the

current EPS recycling processes as it can ruin the entire batch of material.

5. Because the beads are made through an extrusion/palletisation process,

they are not perfectly spherical as are the beads made from suspension

polymerisation process. As a consequence, the final expanded product

could have a higher level of void spaces between the beads which weakens

the product.

All of the above necessitate a need to try for other alternatives for the recycling of

EPS products in other engineering fields to enhance their value as suitable

recycled material. Utilisation in civil engineering applications could be a good

option particularly if a large amount of EPS can be accommodated in an

environmentally friendly or cost effective manner. Use of waste materials

including tyre chips, fibres from PET bottles etc., for various geotechnical

applications is increasing around the world (Eighmy and Magee, 2001; Sherwood,

2001; Inyang, 2003). Hence, the use of waste EPS for the modification of

problematic soils, to enhance its value for reuse or recycle can also be

investigated.

2.7 Summary

So far, Japanese researchers have only considered the use of pre-puff EPS beads

as a component of lightweight fill materials. While their work has been motivated

by the need to manage waste soils, their published results have encouraged a

separate study on the use of crushed waste EPS in earthworks. EPS recycling is

feasible, and studies are progressing, but effective recycling is hampered by the

low bulk density, high volume and fragmented nature of the product. While waste

EPS granules have been used in with horticultural soils to improve a number of

soil characteristics like improving its drainage, lightening heavy soils and

improving water uptake capacity of soils, there are very limited applications

reported in geotechnical engineering.

Chapter 2

37

This thesis is the first of its kind in investigating the possibility of reusing waste

EPS as a swell-shrink modifier in clays and in doing so, may open up the

possibility of using soil-EPS mixes behind retaining walls, under foundations and

as a landfill cover material. The reuse of waste expanded polystyrene in

geotechnical engineering will support the principle of sustainability in

construction.

The mixing of EPS beads with soils would not require specialised equipment. As

an engineered material, soil-EPS mixes can be designed to meet specific

requirements for each application depending on the mix design. EPS beads can

provide cushioning and also take care of loads due to their compressible nature as

is evidenced in packaging; these characteristics may benefit the application of

waste EPS as a soil modifier in expansive soils and as a lightweight cover material

for landfill. The earlier Japanese studies were conducted at higher moisture

contents and utilised chemical stabilisers for strength enhancement. However, it

may be possible to prepare soil-EPS mixes at lower moisture content values such

that the performance can be optimised. With these objectives in mind, Chapter 3

presents a short review of expansive soils.

Chapter 2

38

39

CHAPTER 3 - EXPANSIVE SOILS AND THEIR TREATMENTS ___________________________________________________________

As mentioned in Chapter 1, the inclusion of EPS to expansive soils may offer an

alternative method to chemical stabilisation techniques and other methods for

reducing swell-shrink potential. By substituting part of the expansive soil with

EPS, the soil performance may be improved such that total soil replacement can

be avoided. Intuitively, the performance of the soil-EPS mix will depend on the

nature of the expansive soil.

In this chapter, a background review on expansive soils, considered problematic

around the world including in Australia, is presented. The various factors that

influence the behaviour of expansive soils and their distribution in Australia are

presented. This is followed by their characteristic features like swelling,

shrinkage, desiccation, suction and available treatment options are described.

3.1 Expansive soils

Expansive soils are clays or very fine silts that have a tendency for volume

changes, to swell and soften or shrink and dry-crack, depending on the increase or

decrease in moisture content respectively. These swell-shrink movements in

expansive soils have historically caused frequent problems because of the

unpredicted upward movements of the structures or cracks in the pavements

resting on them. In addition, they also affect the serviceability performance of

lightweight structures supported on shallow and relatively flexible footing

systems and pavements. For example, “doming” (centre heave) and “dishing”

(edge heave) curvatures in foundations would result because of soil movements.

Doming can be due to the long term progressive swelling beneath the centre of

slab and dishing can be due to the cyclic heave beneath perimeter of the

foundation (Masia et al., 2004; Day, 2006).

Expansive soils are a worldwide problem spreading in the semi-arid regions of the

tropical and temperate climate zones across five continents (Chen, 1988). The

primary problem that arises with regard to expansive soils is that deformations are

significantly greater than elastic deformations and they cannot be predicted by

Chapter 3

40

classical elastic or plastic theory. Movement is usually in an uneven pattern and of

such a magnitude that it causes extensive damage to the structures and pavements

founded on them (Nelson and Miller, 1992).

In the U.S.A., it was estimated that expansive soils create more damage to

structures, worth billions of dollars, particularly to light buildings and pavements,

than any other natural hazard, including earthquakes and floods (Jones and Jones,

1987; Nelson and Miller, 1992). Several countries in the world, including

Australia, the United States of America, Israel, India and South Africa have

reported infrastructure damage problems caused by the movement of expansive

soils (Chen, 1988).

3.2 Factors influencing mechanisms in expansive soils

There are many factors that govern the expansion behaviour of soil. The

mechanism of shrinkage and swelling in expansive soils is rather complex and is

influenced by several physical and chemical properties such as clay content, type

of clay mineral, crystal lattice structure, cation exchange capacity, ability of water

absorption and environmental factors like moisture conditions of the site,

magnitude of surcharge load, to name a few. Nelson and Miller (1992)

summarised various factors into three groups, viz., soil characteristics,

environmental factors and state of stresses.

Soil characteristics influence the basic nature of the internal force field, which

depend on the negative surface charges of clay particles and the electrochemistry

related reaction with water. In addition, the swelling capacity of an entire soil

mass depends on the amount and type of clay minerals in the soil, the arrangement

and specific surface area of the clay particles. Furthermore, on a macro scale, the

dry unit weight and physical arrangement of particles will also affect the swell

potential (Nelson and Miller, 1992). Environmental factors influence the change

of the soil-water system that affects the internal stress equilibrium, the state of

stress influences the changes in particle spacing, which in turn influences internal

stress equilibrium (Punthutaecha, 2002). Tables 3.1 and 3.2 present the influence

of various soil and environmental factors (after Nelson and Miller, 1992) and

Table 3.3 summarises the behaviour between non-expansive and expansive soils

(Katti, 1987).

Chapter 3

41

Table 3.1 Soil factors that influence swell-shrink potential (adapted from Nelson and Miller, 1992). Factor Description

Clay mineralogy Montmorillonites, vermiculites and some mixed layer minerals exhibit considerable soil volume changes

Soil water chemistry

Increase in cation concentration and increase in cation valence hold back the swelling

Soil suction Soil suction is an independent effective stress variable, represented by the negative pore pressure in unsaturated soils. Soil suction is associated with saturation, gravity, pore size and shape, surface tension and electrical and chemical characteristics of the soil particles and water

Plasticity Soils exhibit plastic behaviour over wide ranges of moisture content and that have high liquid limits exhibit greater potential for swelling and shrinkage

Soil structure and fabric

Flocculated clays tend to be more expansive than dispersed clays. Cemented particles reduce swell. Fabric and structure are altered by compaction

Dry unit weight Higher unit weights usually indicate closer particle spacing, which may mean greater repulsive forces between particles and larger swelling potential

Table 3.2 Environmental factors that influence swell-shrink potential of soils (adapted from Nelson and Miller, 1992). Factor Description

Moisture content

Changes in moisture in the active zone near the upper part of the soil profile primarily define heave. It is in those layers that the widest variation in moisture and volume change will occur

Climate Amount and variation of precipitation and evapotranspiration greatly influence the moisture availability and depth of seasonal moisture fluctuation. Greatest seasonal heave occurs in semiarid climates that have pronounced short wet periods

Ground water Shallow water tables provided a source of moisture and fluctuation water tables contribute to moisture

Drainage and man made water sources

Surface drainage features provide sources of water at the surface; leaky plumbing can give the soil access to water at greater depth

Vegetation Trees, shrubs and grasses deplete moisture from the soil through transpiration, and can cause the soil to be differently wetted in areas of varying vegetation

Permeability Soils with higher permeability allow faster migration of water and promote faster rates of swell

Temperature Increasing temperature cause moisture to diffuse to cooler areas beneath pavements and buildings

Stress history An over consolidated soil is more expansive than the same soil at the same void ration, but normally consolidated

Loading Magnitude of surcharge load determines the amount of volume change that will occur for a given moisture content and density. An externally applied load acts to balance inter-particle repulsive forces and reduces swell

Chapter 3

42

Table 3.3 Comparison between behaviour of non-expansive soils and expansive soils (adapted from Katti, 1987).

Behaviour Condition Conventional

clayey soil (Non – expansive )

Expansive soil

During saturation from dry to saturated conditions, under a (i) nominal load (ii) as the load increases

Settles Settles more

Heave upwards. Heave goes on reducing and reaches zero at some load and then starts settling

Moisture content with depth say up to around 10 m under free water standing on the top and under fully saturated conditions

Remains almost constant throughout the depth

Near liquid limit at the surface and goes on decreasing rapidly up to around 1 to 1.5 m and then remains constant

Density with depth under saturated condition say up to 10 m depth

Remains almost constant throughout the depth

Very low near the surface and goes on increasing rapidly up to 1 to 1.5 m depth and then remains constant

Undrained cohesion ‘cu’ with depth – vane shear

Remains almost constant

Negligible near the surface and goes on increasing rapidly up to 1 to 1.5 m and then remains almost constant

Density with depth under summer condition

Somewhat more closer to surface and then remains almost constant

High nearer the surface and goes on decreasing rapidly up to 1 to 1.5 m and then almost remains constant irrespective of moisture changes

Lateral pressure with depth for saturated case

Behaves according to Terzaghi’s concept. No lateral pressure up to 2c/�

Negligible near the surface and goes on increasing rapidly with depth up to 1 to 1.5 m and then remains almost constant. Lateral pressure value at 1 to 1.5 m is equal to swelling pressure. Value of swelling pressure at no volume change condition can be as high as 3 to 5 kg/cm2 depending upon soil

K0 at saturated condition Less than 1 Up to 1 to 1.5 m. the value is 15 to 20 and with increase in depth is also greater than 1. 2 to 3 is common

K0 value at saturated condition Less than 1 Up to 1 to 1.5 m. for tolerable wall movement almost 15, then beyond >1, 2 to 3 is common

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3.3 Distribution of expansive soils in Australia

Expansive soils are widespread throughout Australia. The distribution of the

major areas of expansive soils in Australia is shown in Figure 3.1 (Richards,

1990; Look, 2005). The expansive soils include some 75 million hectares of “grey

and brown soils of heavy structure” and 33 million hectares of “black earths”

(Rankin and Fairweather, 1978).

The grey and brown soils are typified by the soils of the “rolling downs”, which

extend through mid-west Queensland from Roma to the Gulf of Carpentaria. The

group is broad, accommodating wide ranges in some properties, particularly

surface structure, reaction profiles and Gilgai. In South Australia, the clay

fractions are illite dominated with 20-30% kaolin; in the east and north they are

montmorillonite-kaolin mixtures with some illite (Wallace, 1988).

Figure 3.1 Distribution of expansive soils in Australia (Richards, 1990).

The “black earths”, overwhelmingly montmorillonite-dominant, include the black

soil of the Darling Downs. The majority of these expansive soils are located

within the 250 to 1000 mm isohyets, extending from North-Western Australia,

thorough the eastern states and into the South-East of Australia (Rankin and

Fairweather, 1978). It has been found that the most troublesome soils in terms of

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volume changes are the black earths, red-brown earths, and the grey and brown

soils of heavy texture. According to Hubble (1972) these soils are found in parts

of Adelaide, Victoria, New South Wales and Queensland.

3.4 Characteristics of expansive soils

Expansive soils are mainly characterised by the swell-shrink potential in relation

to total suction variations through moisture changes, desiccation cracking

behaviour and corresponding strength changes. The expansive soils near ground

surface are generally unsaturated due to desiccation and are commonly self-

mulching, that is, they form a relatively thin surface layer of loose dry granular

material following repeated light wetting and drying (Hubble, 1972).

In the dry state, expansive soils are hard and dense and possess high shear

strength. They are characterised when dry by the existence of the large cracks

(Figure 3.2), which may be up to a maximum of 50 mm in width at the surface,

often tapering and extending down to depths of 1 to 2 m or more in deep

expansive soils and they may be continuously interconnected over several metres

or more in plan dimension. Generally, the spacing and width of cracks are related

(Hubble, 1972; Wallace, 1988).

Figure 3.2 Shrinkage and cracking of expansive soils (Hey, 1999).

During the periods of rainfall, the presence of these open cracks and other planar

voids bypasses the infiltrating water directly to the bottom of the cracks. This

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could allow deep wetting of the expansive soil from heavy rain far more rapidly

than could result from moisture infiltration through the uncracked soil. The entry

of water depends on the previous extraction process. In addition to increasing the

hydrostatic forces, the water is slowly absorbed by the expansive clay. The

gradual wetting of dry soil from the crack bottom causes uplift forces which

further generate heaving of the ground surface surrounding the crack in restrained

environments (Kodikara et al., 1999). Furthermore, high lateral stresses can build

up that result the soil to fail in shear. The more cracks in the clay, the greater the

pathways for water to penetrate the soil, and the quicker the rate of swelling (Day,

2006).

The expansive soils become very sticky upon wetting (Figure 3.3). Furthermore,

they suffer a rapid loss of shear strength associated with expansion and loss of

unit weight as moisture content increase and subsequent release of negative pore

water pressures (Petry and Armstrong, 1989). This is due to the volume changes

occurring because of wetting and drying. These mechanisms result in a

simultaneous increase of the sliding (driving) forces and decrease of the resisting

(shear strength) forces.

Figure 3.3 Wetting and loss of strength in expansive soil (Hey, 1999).

An unsaturated expansive soil will undergo volume changes when the net normal

stress or the matrix suction changes in magnitude (Nishimura, 2001). Bronswijk

and Evers-Verman (1990) observed volumetric expansion by as high as 49% upon

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wetting in natural heavy clays (cited by Kodikara et al., 1999). Furthermore, if

this expansion is prevented, swelling pressure greater than 1 MPa may occur

(Bradford, 1978). The magnitude of swell occurring is directly related to the dry

unit weight and inversely related to the moisture content. In addition, the higher

the volume changes occurring in soils, the greater the potential for cracking in that

soil (Kodikara et al., 1999).

An uncracked sample of a moist clay is virtually impermeable, and infiltration and

drainage under these conditions is very slow. The presence and spacing of open

cracks therefore play an important part in wetting up the soil profile following a

dry period. Large quantities of water from heavy rain, loose surface material, and

other debris are able to enter the cracks before they are closed by soil expansion

and results in damaging differential movement. Furthermore, the combination of

shrinkage cracks and high suction pressure resulting from low moisture content,

allows water to be quickly sucked into the clay, resulting in a higher magnitude of

swell (Day, 2006). As the soil dries, the total suction increases, with subsequent

shrinkage of the soil. Likewise, if the soil is wetted, the total suction decrease, and

the soil expands. In addition, remoulded clay can have higher swell potential than

that of the same clay undisturbed because of the rupture of interparticle bonds that

inhibit the swelling and from the differences in fabric (Mitchell and Saga, 2005).

3.5 Effects of expansive soil on different structures

3.5.1 Foundations

Expansive soils can damage foundations by uplift as they swell with increase in

moisture content. In addition, moisture content variations in expansive soil can

cause structural problems through differential movement of the structure. There

could be non-uniform movement in the structure if the moisture content and/or

soil type differs at various locations under the foundation. Sometimes, these

movements may be limited to a small area. These isolated movements of sections

of the structure can cause damage to the foundation, evidenced by cracking of the

slab or foundation, cracking in the interior or exterior wall faces, uneven floors

and/or misaligned doors and windows. This type of movement is generally related

with slab on grade construction. However, this type of movement may also occur

in structures with basements and crawlspaces.

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Another effect of expansive soils is additional horizontal pressure applied to

foundation walls found in basements and crawlspaces. Increased moisture in the

expansive soils adjacent to the foundation wall can exert tremendous force as they

expand and increase the lateral pressure applied to the foundation wall. If the

foundation wall does not have sufficient strength, minor cracking, bowing or

movement of the wall may occur. Serious structural damage to, or failure of, the

wall may also occur.

3.5.2 Retaining walls

Expansive soils often create long-term problems as backfill materials behind

retaining walls. The lumpy and cohesive nature of expansive soils often makes it

difficult to recompact them to states of uniform moisture content and unit weight

that will ensure minimal future settlements, minimum swelling potential or

minimum lateral earth pressures. Beyond the obvious problems of large and

protracted surface settlements, expansive soil backfills require significantly

stronger retaining structures such as basement walls to withstand the larger

horizontal earth pressures than are exerted by non-expansive soil backfills

(Hamilton, 1977). Expansive soils are relatively impermeable, which makes

adequate drainage in back of the wall impossible. The wall, therefore, must be

designed to resist water pressure in addition to the pressure of the earth backfill.

This is uneconomical and may be needlessly wasteful (Duncan, 1992).

3.5.3 Landfill cover systems

Compacted clays are generally used as hydraulic barrier layer in landfill covers

because clay fraction of the soil ensures low hydraulic conductivity. In the

absence of suitable impermeable natural clay soils near the landfill sites,

compacted mixtures of bentonite and sand have been used to achieve the desired

low hydraulic conductivity (Kenny et al., 1992; Van Ree et al., 1992; Daniel and

Wu, 1993).

There are, however, some draw backs with the use of clay or sand-bentonite

mixes as a cover material. Clay or bentonite mixtures possess high swell-shrink

potential and under drying conditions, large scale and small scale cracks either as

surface or internal cracks can form, resulting in an interconnected network of

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preferential flow paths. These eventually result in increased leakage rates through

the landfill. Compacted clay layers are especially vulnerable because they have

low resistance to wet-dry cycles (which causes desiccation cracking), freeze-thaw

cycles (which increase hydraulic conductivity), and distortion caused by

differential settlement (which can cause tensile cracks to form) (Koerner and

Daniel, 1997).

Tay et al. (2001) observed that cracking only occurs when sand-bentonite

mixtures undergo more than 4% volumetric shrinkage when air dried.

Furthermore, they observed that sand-bentonite mixtures compacted at a moisture

content that would not result in desiccation cracking upon drying, may swell upon

access to further water and may then crack on subsequent drying.

3.6 Expansive soil treatment options

To take care of the various effects mentioned above expansive soils need

treatment. The various treatment options, which range from a simple primitive

solution to a costly sophisticated one, for treating expansive soils before and after

construction of structures and highways are listed below (Chen, 1988; Nelson and

Miller, 1992; Bullen, 2002; Day, 2006).

• Chemical additives

• Prewetting

• Soil replacement with compaction control

• Moisture control

• Surcharge loading

• Lateral confinement

• Thermal methods

• Deep foundation systems

Generally, the selection of treatment option (s) is not a straight forward procedure.

The choice of an appropriate method depends on the preliminary site investigation

and evaluation of the soil properties (Nelson and Miller, 1992). The options

available to engineers in remote arid areas are most likely to be limited to

minimization of subgrade moisture changes or to stabilisation of the subgrade.

Replacing expansive foundation soils with non-expansive soils such as sand is a

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simple and easy solution to eradicate expansive soil problems. However, these

tasks are expensive and time consuming (Puppala and Musenda, 2000). Hence,

the material modification with various chemical additives like lime, cement and

fly ash are commonly performed on expansive soils because these admixers

control the potential of soils for a change in volume. Of late, there is a trend to use

fibres and other materials for the modification of these soils (Al-Wahab and El-

Kedrah, 1995; Basma et al., 1998; Ziegler et al., 1998; Loehr et al., 2000; Miller

and Rifai, 2004; Punthutaecha et al., 2006).

3.6.1 Lime stabilisation

Lime stabilisation is the one of the oldest chemical stabilisation methods which is

well recognised and widely practised for structural improvement of many types of

soils and aggregates. The addition of lime neutralises the electrical imbalance in

the soil particles with appropriate ions. This in turn reduces the plasticity of soil

and increases its workability. In addition, the compressive strength and load

bearing properties are also improved (Bhattacharja et al., 2003). Currently, lime

stabilisation has been used in highways, railroads, and airport construction

projects to improve roadbeds and pavement supporting layers. It is also used to

improve the properties of the soft soils and dredged soils (Bergado et al., 1994).

Examples of the specific applications of lime stabilisation are construction

embankments, soil improvements under foundation slabs and lime columns

(Brandl, 1981).

Amongst the different types of lime that can be used for soil stabilisation (Table

3.4), the slaked or hydrated lime and quick lime, are the most commonly used

varieties. Slaked lime (Calcium hydroxide) and quick lime (Calcium oxide) react

with soils to form cementitious compounds like calcium silicates, which increase

soil strength and durability (Lambe et al., 1990).

Lime improves engineering properties of the soils. Addition of lime converts

clayey soil to a non plastic granular type soil (Broms and Boman, 1979). Lime

treatment reduces the compressibility characteristics of soft soils and dredged

soils.

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Table 3.4 Different types of limes (adapted from Punthutaecha, 2002).

Chemical symbol Name(s) CaO Calcium oxide, quick lime or un-slaked

lime Ca(OH)2 Calcium hydroxide, hydrated lime or

slaked lime CaCO3 Calcium carbonate or lime CaO.MgO Dolomitic quick lime Ca(OH)2.MgO Normal hydrated or monohydrated

dolomitic lime Ca (OH)2. Mg (OH)2 Pressure-hydrated or dehydrated dolomitic

lime

However, lime stabilisation methods have some limitations. For example, lime

stabilisation methods are affected by leaching. It was observed from field studies

that swelling and plasticity index reverted almost to those of natural untreated

soils (Bhattacharja et al., 2003). They are not appropriate in project sites where

significant strength improvements are essential or where granular deposits are

encountered. This is due to the fact that lime itself has neither appreciable friction

nor cohesion. Thus, after certain percentage of lime addition, a strength gain is not

found in the soils. Similarly, granular soils have no cations for the replacement by

lime ions (Bell, 1996). In addition, lime also induces distress problems in lime

treated sulphate-rich soils because of ettringite formations and creating a “roller

coaster” effect in roads and structures (Kota et al., 1996; Puppala et al., 2002).

Furthermore, adding a quick lime is a health and safety hazard. In spite of these

limitations lime is the most commonly used chemical stabiliser in treating

expansive soils.

3.6.2 Cement Stabilisation

Cement is generally the best type of admixture for effectively stabilising a wide

variety of soils, including granular materials, silts and clays. Stabilisation with

cement for soft soils or expansive soils involves mixing of soils with cement and

water, and subsequent compaction of this mix to a high density makes the material

more resistant to variations in physical, thermal and chemical stresses

(Winterkorn and Pamukcu, 1991). The addition of cement reduces the plasticity

and increases the shear strength of the soil (Kezdi, 1979), which may result in the

reduction of potential volume change of expansive soils (Chen, 1988). However,

cement stabilisation has a number of limitations such as high cost, possible

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corrosion of the soil environment, brittle failure and low temperature cracking as

result of the hydration and moisture loss, and proneness to sulphates attack

(Punthutaecha, 2002).

3.6.3 Fly ash Stabilisation

Fly ash is a by-product of coal from thermal power plants. Based on the original

source of coal that is used in generation of power, fly ash is classified as Class C

or Class F. Class C fly ash is self-cementing because of the presence of 20 – 30%

of calcium Oxide (CaO) and can be used as stabiliser without any chemical

additives. However, Class F fly ash, with a low free-lime content, is not effective

as a soil stabiliser without the addition of lime as a source of calcium (Petry and

Little, 2002).

The addition of fly ash to a soil can produce stabilising effects through two basic

reactions viz., short-term or immediate reactions and long term reactions

(Diamond and Kinter, 1965; Usmen and Bowders, 1990; Zaline and Emin, 2002).

The immediate reactions cause flocculation and agglomeration of the dispersed

clay particles due to the ion exchange at the surface of the soil particles, which

enhance the workability characteristics in soils and provide immediate

improvements in the swell, shrinkage and plasticity characteristics. With time,

further gain in strength may be acquired through the formation of cementitious

materials (Nicholson and Kashyap, 1993).

Sometimes, to improve the engineering properties of fly ash mixed soils other

chemical additives are also added. For example, the use of fly ash either with lime

or cement can enhance soil strength and stiffness depending on the lime or cement

contents (McManus et al., 1993). Stepkowska (1994) used fly ash and lime to

decrease the swelling and shrinkage of clay while increasing its strength. Puppala

et al. (2000) used fly ash to decrease the swelling of the expansive soils rich in

sulphate content.

The rate of fly ash reactions are affected by fineness (or surface area) of the soil

particles, chemical composition, fly ash mixture, soil types, temperature,

moisture content, and the amount of stabilisers use in the mixture (Usmen and

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Bowden, 1990). However, fly ash is known to cause environmental problems due

to the leachability of their heavy metal content into soil or water (Ricou et al,

1999). Hence, proper care must be exercised in its utilisation.

3.6.4 Other innovative methods

One method of controlling swell-shrink potential in expansive soils is to stabilise

them with admixtures that prevent volume changes, if possible, or adequately

modify the volume change characteristics of an expansive soils (Kehew, 1995).

Based on this principle, other innovative mechanical additives such as sand,

geogrids and polymeric materials like fibres, tyres and foam chips were

investigated by some investigators as discussed below.

3.6.4.1 Mechanical alteration using sand

Mowafy et al. (1985) have studied the effect of addition of sand on the swelling

properties of an expansive soil having a liquid limit of 86%, plastic limit of 43%

and plasticity index of 43%. The sand was mixed from 0% to 100% in increments

of 10% and also with initial moisture contents ranging from 5% to 20% in

increment of 5% for all samples. They observed that with an increase in sand

content and corresponding reduction in clay content, there was a decrease in the

swelling pressure as shown in Figure 3.4 for all moisture contents. They attributed

this swell pressure reduction to the larger capillary canals in the soil pores and the

corresponding reduction in soil suction. Furthermore, they observed an increase in

the rate of deformation of swell-susceptible clay due to addition of sand, and due

to the increase in soil permeability. They suggested mixing coarse fractions of

granular materials with swell-susceptible soils to reduce swelling potential.

Similarly, Basma et al. (1998) studied the effects of mixing local sand with

expansive soils on their swelling potentials. Sand contents of 40% (60% clay),

44% (56% clay) and 52% (48% clay) were studied. All the specimens were

moulded at their natural moisture content and maximum dry unit weight. They

observed that as the sand percent increased, the swell percent decreased. An

increase in sand percent from 40% to 52% resulted in a decrease from 8.56% to

4.0% in the swell percent and a decrease from 182 kPa to 110 kPa in the swell

pressure.

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Figure 3.4 Relationship between swelling pressure and clay content at same initial moisture content (Mowafy et al., 1985).

They attributed this reduction to the large capillary canals in the soil pores and the

corresponding reduction in soil suction, in agreement with Mowafy et al. (1985).

However, this could also be due to the reduction in surface area of the clay

fraction due to the sand replacement.

3.6.4.2 Geogrids

Al-Omari and Hamodi (1991) studied the influence of tensile geogrids on the

control of soil swell potential by performing swelling tests using a large

oedometer apparatus. The reinforcement was in the form a cylindrical geocell of

grid installed in a vertical position into the expansive soil to counteract heave. The

grid stiffness considered were 240, 500, 740 kN/m, plasticity index considered

were 41, 47 and 115%, and applied surcharge considered were 7, 50 and 100 kPa

They observed that there is a significant reduction in swelling due to the

reinforcement. Furthermore, the reduction increased with the increasing stiffness

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of the geogrid as shown in Figure 3.5. They observed that the improvement factor,

defined as the difference between the final swell of un-reinforced specimen and

the final swell of corresponding reinforced specimen divided by the final swell of

un-reinforced specimen, ranged from 17 to 51% depending on the grid stiffness

and plasticity index and surcharge pressure.

Figure 3.5 Relationship between swell and square root of time for different

stiffnesses for at surcharge of 7 kPa (Al-Omari and Hamodi, 1991).

3.6.4.3 Using polymeric materials

Fibres in control of swell-shrink potential

Puppala and Musenda (2000) investigated the use of randomly oriented

polypropylene fibres, 25 mm to 50 mm in length, in stabilising expansive soils,

Irving clay (LL = 82%) and San Antonio clay (LL = 73%). In tests involving

0.3%, 0.6% and 0.9% fibres by dry weight of compacted soil, they observed a

slight reduction in shrinkage. However, the conventional swelling measured in the

oedometer test showed an increase of about 8 to 41% when the soils were treated

with fibres (Table 3.5). They attributed this increase in free swell to a more

uniform distribution of moisture in the compacted specimens caused by moisture

paths created by the fibres.

The use of 0.9% short fibres reduced the swell pressures of Irving clay by 11.7%

where as 0.9% long fibres reduced the swell pressure by 15%. In the San Antonio

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clay, the swell pressure was reduced by nearly 44% with the inclusion of 0.9%

fibres (Table 3.5).

Table 3.5 Free vertical swelling strains and swell pressures (Puppala and Musenda, 2000).

Loehr et al. (2000) studied the influence of fibre reinforcement in the reduction of

swell potential of expansive soils. The soil has a liquid limit of 59.4% and

plasticity index of 38.9%. Through a series of one-dimensional free swell tests

they observed that the relative reduction in free swell was much larger for

specimens compacted wet of optimum moisture content (44% reduction in free

swell) than for those compacted dry of optimum (22% reduction in free swell) as

shown in Figure 3.6. In addition, they noted that “wet” and “dry” specimens

showed similar absolute reductions in free swell with increasing fibre contents

indicating that swell displacements were less dependent on the compaction

moisture content. Furthermore, they observed that reduction in swell potential was

dependent on the specimen size. For example, in 102 mm diameter specimens, 4%

reduction was observed between non-reinforced and 0.4% reinforced specimens

whereas no apparent reduction was observed in 64 mm diameter specimens. They

observed that the magnitude of the reduction of free swell was generally

proportional to the amount of fibres added to the soil.

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Figure 3.6 Variation of swelling strain with fibre content for specimens prepared on

wet and dry of optimums (Loehr et al., 2000).

Punthutaecha et al. (2006) have observed the volume change behaviour of

expansive soils stabilised with fibres by performing three dimensional free swell

tests using soil specimens of 105 mm diameter and 115.5 mm height. The amount

of heave was measured in both vertical and diametral directions. For three

dimensional shrinkage tests, 63.5 mm diameter and 152.4 mm height slurry

specimens were used. Two types of fibres were used, i.e. polypropylene fibres and

nylon fibres. The addition of different fibres gave different results as shown in

Figure 3.7. Polypropylene fibres showed an increase in swell behaviour after

0.2% dosage level whereas nylon fibres showed decrease in swell behaviour for

all dosage levels. The increase in swell was attributed to the difficulty in

compaction and hence the creation of large voids when polypropylene fibres were

used.

On three dimensional shrinkage strains of fibres treated soils, they observed that

both polypropylene and nylon fibres decreased the shrinkage strains (Table 3.6). It

is interesting to note that the maximum decrease was observed at 0.2% fibre

content. Furthermore, they observed plateau conditions at higher dosage levels.

They attributed the decrease in shrinkage strain to the increase in cohesion due to

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the inclusion of fibres. In addition, they suggested that soils with higher amounts

of fines could be better stabilised with fibres because of better adhesion between

soils and fibres.

Figure 3.7 Volumetric swell strain of fibre treated soil compacted at 100% of dry unit weight (Punthutaecha et al., 2006).

Table 3.6 Average three-dimensional shrinkage strains of fibre treated soils (Punthutaecha et al., 2006)

Fibres in the control of desiccation cracking

In the current study it was hypothesised that addition of recycled EPS beads

would control the desiccation cracking behaviour of clay soils. Earlier some

researchers have attempted to control desiccation cracks by mixing fibres with the

soil. These are briefly discussed in the following review.

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The influence of short fibrillated polypropylene fibres with 0.0, 0.2, 0.4 and 0.8%

in contents, with an optimum fibre length of 12.7 mm, in controlling tension

cracks in a low plasticity clay having a liquid limit of 54%, plasticity index of

26% and optimum moisture content of 20.5% was studied by Al Wahab and El-

Kedrah (1995). They observed that under controlled compaction moisture, the

inclusion of short fibres reduces both the amount of cracking and the

shrinkage/swelling for the type of clay considered. For example, the crack index,

defined as ratio of area of cracks to total surface area of soil sample, declined

from 4.0 x 10-3 to 2.2 x 10-3 for samples exposed to two shrink- swell cycles. In

addition, they also observed that the amount of cracking reduced exponentially

with the increasing number of shrink-swell cycles. In general the reduction in

crack index was about 25% to 45%.

Similarly, Ziegler et al. (1998) studied the effectiveness of short polymeric fibres

in strengthening the soil and preventing the crack development in compacted

clays subjected to a series of drying and wetting cycles. Synthetic clays were

prepared by mixing different proportions of kaolinite, calcium bentonite and/or

sodium bentonite. Plasticity indexes ranging from 25 to 100% were used. The

fibre contents used were 0%, 0.1% and 0.3%. They observed that, as shown in

Figure 3.8, the addition of fibres in the order of 0.3% for a clayey soil having a

plasticity index (PI) of 100% influenced the crack dimensions and crack

distribution. For soils with fibres numerous cracks of small width and length were

noticed. However, the cracks penetration into the soil was not as deep as for soils

without fibres.

Figure 3.8 Variation of crack sizes and distribution with and without fibres (Ziegler et al, 1998).

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In another study, Miller and Rifai (2004) studied the influence of fibre

reinforcement for waste containment soil liners. Cracks reduction was analysed

for the addition of 0.2, 0.4, 0.6 and 0.8% fibre contents. They observed that

increasing the fibre content from 0.2% to 0.8% significantly increased the crack

reduction from 12.3% to 88.6% respectively as shown in Figure 3.9. However,

they observed that exceeding the fibre contents by more than 0.8% was not

practical due to difficulty in fibre-soil mixing to obtain uniform distribution of

fibre in the soil. In terms of hydraulic characteristics, they noticed that the

addition of fibres more than 1% significantly increased the hydraulic conductivity

and 0.4% to 0.5% fibre content maintained the hydraulic conductivity within

acceptable limits.

These studies indicate that there is potential for the use of fibres in controlling the

desiccation cracking of clayey soils. The mechanism of control is through tensile

resistance of fibres. Hence, in the current research it was hypothesized that

recycled EPS beads can control the desiccation cracking in clayey soils by similar

or other mechanisms such as compression and elongation.

Figure 3.9 Crack reduction with various fibre contents

(after Miller and Rifai, 2004).

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Tyre Chips

Al-Tabbaa and Aravinthan (1998) investigated the effect of shredded tyre pieces

on the swelling behaviour of Keuper Marl clay (PI =12%). Two rubber contents

were employed: 8% for 1-4 mm tyre pieces and 15% for 4-8 mm tyre pieces. The

swelling test was conducted on one-dimensional consolidation cell. They

observed that with an increase in rubber content the free swell on the dry side of

optimum and at the optimum was reduced (Figure 3.10), while, no significance

difference was observed on the wet side of the optimum because of the near

saturation of specimen. They attributed this reduction to the presence of hairlike

cracks which accommodated the water.

Figure 3.10 Variation in swelling with tyre chips (Al-Tabbaa and Aravinthan, 1998).

In another study Cocka and Yilmazz (2004) studied the use of pulverised rubber

from tread of tyres and bentonite added fly ash as a liner material. The pulverised

rubber was in a sand-size range with same particle dimensions and shapes as sand.

On the swell pressure characteristics they observed that addition of rubber with fly

ash and bentonite mixture reduced the swell pressure. For example, for 90% fly

ash, 5% rubber content and 5% bentonite content, the swell pressure was 110 kPa.

When compared with 90% fly ash and 10% bentonite content and 0% rubber

content, this is nearly 100% less.

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Foam chips

Sorochan (1991) conducted tests to study the effect of an addition of highly

compressible polymer materials such as plastics to the soil on its swelling

pressure. It was observed that the addition of foam plastics in the form of chips

was helpful in compensating the swelling pressure and caused significant decrease

in its magnitude (Table 3.7). The foam plastics were added to the soil while it was

being packed into the consolidation apparatus to a ratio of 2 to 4% by volume.

The addition of highly compressible material to the soil reduced the swelling

pressure by 24 to 62%. In addition, by increasing the density of the foam plastic

chips from 0.017 t/m3 to 0.0666 t/m3, for 2% of volume, the decrease in swelling

pressure was from 24.4% to 43.2%. Furthermore, the placement of porolon, a soft

cushion material, in the form of 5.3 mm layer at the bottom of the apparatus in

addition to foam chips, reduced the swelling pressure by 91%. The reduction of

swelling pressure was attributed to compressibility of the polymer material.

Table 3.7 Swelling pressure of natural soil and soil with polymer additives (adapted from Sorochan, 1991).

Type of soil Volumetric Percentage of additive*

Swelling pressure, kPa

Decrease in swelling pressure, %

Natural soil Density = 1320 kg/m3 Optimum Moisture Content = 15%

66.0

0

Soil with additives (i) with addition of foam plastic � = 17 kg/m3 � = 66.6 kg/m3

2 4

2 4

50.0 42.0

37.5 25.0

24.4 36.4

432 62.1

(ii) with addition of porolon 21.5 6.0 91.0

3.7 Possible use of soil mixed with EPS beads

The discussion thus far shows the potential of using polymeric materials such as

tyres, fibres and foam chips for the treatment of expansive soils. In a similar

category, recycled EPS beads when mixed with expansive soils can be used for

varied applications as described in the ensuing sections.

Chapter 3

62

3.7.1 Backfill behind retaining wall

To avoid the failure of retaining walls located in expansive soil regions having

expansive clay as backfill, Petry and Armstrong (1989) suggested that the

expansive soil mass surface behind the retaining wall should be cut back to at

least 45 degrees from the horizontal and should be filled with non-active, free

draining material, such as clean granular sand or gravel, so that as it swells, it will

not impose loads on the wall. Furthermore, a system of weep holes and filter

protected drains are to be installed at the base of the wall in the backfill as shown

in Figure 3.11. This is because when clay backfill is compacted to a high dry

density and low moisture content, it develops high swelling pressures upon water

infiltration.

This process needs the free draining backfill to be imported from other areas.

Instead of filling with other soils, the expansive soils can be mixed with waste

EPS beads and compacted as lightweight fill.

Figure 3.11 Retaining wall backfill treatment (Petry and Armstrong, 1989).

3.7.2 Foundations

The differential movements in the foundations can be controlled by the use of

soil-EPS mixes. The in-situ expansive soils can be mixed with waste EPS beads

and can be compacted below the foundations. Through this way any isolated

movements can be taken care of by the EPS beads through elastic rebound nature.

halla


Chapter 3

63

3.7.3 Landfills

The use of EPS as a soil modifier is expected to enhance the property of clay

soils. That is the potential of swelling and shrinking can be reduced to make the

soils, which would otherwise be discarded, useful in applications such as

lightweight landfill cover materials. This may reduce the desiccation cracking in

compacted clay layers and reduce the leakage rates.

According to Mitchell and Saga (2005), the specific surface area of smectites

which are the predominant minerals in expansive soils, can be very large. The

primary surface area, that is, the surface area exclusive of interlayer zones, ranges

from 50 to 120 m2/g. The secondary surface that is exposed by expanding the

lattice so that polar molecules can penetrate between layers can be up to 840 m2/g.

Hence, to treat expansive soils, this surface area can be reduced by adding suitable

admixer(s).

It can be noted from the above studies that the reduction occurs with the addition

of admixers to expansive soils, either in combination or individually through both

mechanical and chemical means. In this context, any addition of material such as

sand, fibres, tyre chips etc., can reduce the surface area considerably through soil

replacement, which will lead to a reduction in swell pressure and swelling

deformation.

Therefore, within the context of the current study, it can be proposed that the in-

situ soil be modified with recycled EPS beads to reduce the surface area of the

clay.

3.8 Summary

Expansive soils are wide spread throughout the world. The main problem

associated with these soils is their swell-shrink potential. There are different

treatments options available for controlling these movements. However, each

method has certain limitations necessitating the need for further research using

alternative materials.

Chapter 3

64

As mentioned in Chapter 2, research elsewhere shows that EPS blocks can be

used as a compressible inclusion and EPS beads can be mixed with soils to

produce soil-EPS mixes with new characteristics for various geotechnical

applications. Based on the published results, a novel idea of mixing waste EPS

granules as a mechanical admixer with expansive soils was conceived. It was

hypothesised that by mixing EPS granules with expansive soils, the swell-shrink

potential will be reduced through partial soil replacement; decrease in unit weight

and also because of the cushioning effect of EPS through its elastic behaviour. In

addition, with clay replacement the reduction of surface area will cause a decrease

in swelling and shrinkage.

The new and innovative method of treating expansive soils with recycled EPS

provides an opportunity to use unwanted expansive soils and waste EPS in various

applications such as under footing, backfill behind a retaining wall and landfill

cover materials. With these points in view, a scoping study with dredged soil from

Brisbane River was performed. The findings were reported in the ensuing chapter.

65

CHAPTER 4 - SCOPING STUDIES WITH A DREDGED SOIL ___________________________________________________________

As indicated in Chapter 1, the current study was intended to investigate the

possibility of using recycled EPS beads as a swell-shrink modifier of expansive

soils. Chapter 2 presented various properties of EPS which may affect its

performance as a soil modifier. Chapter 3 described how the expansive soils can

cause serious damage to various structures and discussed the need to develop

appropriate method(s) to improve the soil characteristics. In this chapter, the

results of a preliminary investigation on the effects of EPS inclusion to a dredged

soil are described.

Early in this stage, it was realised that the soil to be tested should serve the

intention of observing the influence of EPS on heavy clays. While searching for a

suitable soil for this purpose in and around Brisbane, it was noticed that Port of

Brisbane Corporation was conducting dredging operations and begun placing the

dredged soil at Brisbane airport, for the filling the low-lying areas (Port of

Brisbane, 2001). The dredged soil was subsequently selected to start the

investigation on the effect of mixing recycled EPS beads. In subsequent chapters,

the resulting composite formed by Soil with EPS will be termed as SWEPS mix.

There are a number of reasons for the selection: i) similar soils have been studied

in the past, ii) the dredged soil is a waste material and its reuse would be

welcomed iii) the soil is a highly plastic clay and iv) the soil is available in huge

quantities and has not found practical use.

4.1 Dredged soils

Similar to the situations in many ports and harbours around the world, for

accessibility and to facilitate navigation of ships, Port of Brisbane conducts

regular maintenance and capital dredging activities. Because the sediments are

usually dredged from the bottom of water bodies, dredged soil contains high water

content in the range of 500 to 1000 % (Kamon et al., 2000). In addition,

depending on the proximity to the sources of pollution such as industrial or

municipal as well as urban and agricultural non-point discharges, it also contains

contaminated sediments and/or organic matter. Consequently, this is considered as

Chapter 4

66

a waste material and its disposal is one of the challenges due to the strict

environmental regulations.

Traditionally, the most common and least expensive disposal of the dredged soil

is open-water disposal. However, the pollutants present in the dredged soil often

can cause detrimental environmental impacts to the ecology of water bodies.

Hence, this method of disposal is restricted with the introduction of national and

international laws (Millrath et al., 2002). The permissible and threshold limits for

the disposal of the dredged soil to water bodies and land disposal vary

considerably. In Australia these are governed by ANZECC (1992) guidelines. The

strict implementation of these environmental laws has driven up the cost of

disposal.

Owing to the availability of the dredged soil in huge quantities and the shortage of

good quality material for various construction purposes for economic

development in the coastal areas, the use of uncontaminated dredged soil as a

construction material has a strong economical advantage in the aspect of the

reutilisation of waste matter. In view of this, ports worldwide try to use a

multifaceted approach including disposal, recycling, separation, dewatering,

stabilisation, decontamination and reuse of the dredged soil (Millrath et al., 2002).

The use of dredged soils in construction has dual advantages. Firstly, it reduces

the need for importing soil at high transporting cost and secondly, it increases the

life span of disposal sites by reducing the waste flow (Tsuchida et al., 2001).

Dredged soil comprises mainly of clays, silts and sand mingled with rocks and to

some extent organic matter. The properties of marine soils that are most

commonly dredged for maintenance purposes are given in Table 4.1.

Dredged soils are usually soft and compressible which renders them ineffective

for use in their native state. Consequently, the use of dredged soils as a structural

fill requires a significant reduction in moisture content and an increase in

workability. This is because with its high moisture content, the strength,

compressibility and durability of the material may be unsatisfactory (Wiley III et

al., 2002).

Chapter 4

67

Table 4.1 Properties of marine clay at different locations of the world.

1Ahmad and Peaker (1977); 2Fang and Owen (1977); 3Katti et al. (1977); 4Rajasekaran and Rao (1998); 5Minegashi et al. (2002); 6Bergado et al. (1996); 7Satoh et al. (2001); 8Miura et al. (1987); 9Mohan and Bhandari (1977); 10Tsuchida et al. (1996) ; 11Yoonz et al. (2004).

There is evidence that cementing additives can effectively improve some of the

mechanical properties of dredged soils, such as resistance to compression,

improvement in strength and durability (Ogino et al., 1994; Gulin and Wikstrom,

Natural water content (%)

Liquid limit (%)

Plastic limit (%)

PI (%)

Particle density (t/m3)

Silt (%)

Clay (%)

Singapore marine clay1 50-83 50-90 18-22 30-50

James Bay marine clay(Canada)1

22-38 26-38 14-18 5-18

Leda clay Ottawa(Canada)1 28-50 20-45 18-24 5-20

Norwegian soft clay1 27-40 25-36 17-20 6-20

Gulf of Mexico2 72 34

Gulf of Amine2 163 121 51

Bombay (M1)3 80-100 65-75 20-25 25-35 35-55

(M2)3 80-100 50-70 25-40 20-45 40-65

(M3)3 60-100 55-85 25-40 15-30 60-80

(M4)3 60-125 60-100 30-55 10-40 35-75

Madras clay (India)4 88 33

Kanto Loam (Japan)5 116.5 143.7 74.8 2.81

Soft Bangkok clay6 76-84 103 43 60 28 69

Dredged Ariake clay, Japan7

2.5 m depth8

6.5 m depth8

10.5 m depth8

84 162 122 108

63.8 125 97 79

26.9 55 43 39

36.9 70 54 40

2.69

Visakhapatnam (India)9

80-90

65-97

40-45

24-55

2.65

40-70

Kandla (India)9 35-75 55-80 20-35 20-50 2.72 30

Willingdon, Cochin (India)9 75 109 40 69 2.52 53

Tokyo Bay mud10 100.4 38.9 41.3 24.5

West-Southern part of Korea11

132 45 24 21 2.66 93

Chapter 4

68

1997; Hoikkala et al., 1997; Den Haan, 1998; Tremblay et al., 1998; Kamon et al.,

2000).

In chemical treatments, special machineries are needed which cause the cost per

unit volume of the treated soils to become prohibitive. To make treated soils more

competitive to conventional fills it is necessary to find their value added

properties. The addition of lightweight soil additives such as EPS and airfoam is a

good option for commercially viable reuse of dredged soils since lightness is a

property effective to increase the economic efficiency (Okumura et al., 2000).

As discussed in Chapter 2, the use of EPS beads with dredged soil was

investigated in Japan for port and harbour structures and for construction surplus

soil (Miki, 1996; Hirasawa et al., 2000; Okumura et al., 2000; Yamane et al.,

2000; Satoh et al., 2001; Tsuchida and Kang, 2003; Yoonz et al., 2004). In these

studies, moisture content was in the order of 2.5 times the liquid limit and pre-puff

EPS beads were used for mud dispersion, to adjust the unit weight and to enhance

the workability of the composite thus formed (Tsuchida et al., 2001; Satoh et al.,

2001).

The current scoping study was intended to consider the limiting factors that affect

the placing and/or compaction and the miscibility of crushed waste EPS beads and

soil for land applications. In contrast with the earlier studies, EPS was mixed at a

moisture content that is close to the optimum moisture content of the dredged soil

to achieve better strength and compressibility characteristics.

4.2 Waste EPS

In the current research, crushed EPS pieces from produce-boxes were collected

from an EPS collection centre situated in Archerfield, Brisbane. This is one of six

EPS reprocessing sites in Queensland and forms a part of the national EPS

reprocessing network in Australia (PACIA, 2005).

The produce boxes before and after crushing at the collection centre is shown in

the Figure 4.1a and 4.1b. The recycled EPS vary in size from what is shown in

Figure 4.1b to that shown in Figure 4.2b. Based on a preliminary testing, it was

Chapter 4

69

observed that large EPS pieces as shown in Figure 4.1 (b) were difficult to mix

and compact in a standard compaction mould. Moreover, large EPS pieces would

have higher compression on loading and showed some rebound tendency upon

unloading; hence, the particle size in the range of 1.2 mm to 9.5 mm was selected.

Even though different produce boxes were available at the EPS collection centre,

for the present research produce boxes of the same type were used. The mean

density of the EPS pieces is 20 kg/m3.

In the laboratory, the larger EPS pieces were crushed in a blender to obtain 90%

of the particles within the range of 1.2 mm to 9.5 mm. While most of the recycled

EPS beads from packaging boxes may have the different properties, as an added

precaution and to avoid any material variability that would have arisen from using

different batches of crushing, in the current research, all the recycled EPS beads

were obtained from the same batch.

The recycled EPS used in this study was of non-fire retardant type. Generally, for

packaging products flame retardants are not used as additives because it will

increase the cost of production (Horvath, 1995).

(a) (b) Figure 4.1 Produce boxes (a) before crushing and (b) after crushing.

The shape and relative size of the pre-puff EPS beads and recycled EPS beads are

illustrated in Figure 4.2a and 4.2b, respectively. As can be seen from these

figures, in contrast with the pre-puff EPS beads, the recycled EPS beads varied in

size considerably and were irregular in shape. Note that pre-puff EPS beads were

used in the earlier studies (Tsuchida et al., 1996; Satoh et al., 2001; Minegashi et

Chapter 4

70

al., 2002; Yoonz et al., 2004) and mixed with dredged soils to form lightweight

flowable fill materials.

(a) (b) Figure 4.2 Size and shape of the EPS beads

(a) pre-puff beads and (b) recycled beads.

The particle size distribution curve of the recycled EPS beads is shown in Figure

4.3. The mean diameter D50 of the recycled EPS particles is 4.5mm.

0

20

40

60

80

100

0.01 0.1 1 10 100Particle size , mm

Per

cen

tag

e fin

er

Figure 4.3 Particle size distribution curve recycled EPS beads.

4.2.1 Effect of temperature on EPS

According to AS 1289.2.1.1 – 1992, for moisture content determination by oven

drying method, soil samples have to be kept in an oven for 24 hours at 105°C.

Hence, prior to determining the moisture contents of soil-EPS mixes, the

influence of temperature on the mass and volume of EPS beads was investigated.

Chapter 4

71

For this purpose, three sizes (10, 20 and 30 mm side) of EPS cubes were prepared

by hot wire cutting from EPS blocks. All the specimens were tested at 105°C ±

2°C for a duration of 24 hours as per the standard specification.

As explained in Chapter 2, evidence suggests that the highest service temperature

that EPS can withstand is 70°C (Table 2.2). Furthermore, EPS will melt at 93°C

and start flowing away from flame at around 120°C (Thompsett et al., 1995).

However, the effect of temperature variation on EPS dimension and mass had not

been satisfactorily explained in the past. Hence, it was decided that in the present

investigation, the effect of temperature variation from 40 to 100°C should be

considered.

Table 4.2 Effect of temperature on mass and volume of EPS cubes.

Side Dimensions, mm Mass, g

Before heating

After 24 hr heating at temperatures of

Before heating

After heating

40 - 70°C* 80°C 100°C 40 -100°C**

10 10 0.7 0.3 0.02 0.02

20 20 1.4 0.6 0.16 0.16

30 30 2.1 0.9 0.54 0.54

Volume reduction, %

0 65.7 97.3

Note: *within this range the dimensions are unaltered. **within this range the mass is constant. Table 4.2 shows the test results, which indicate that temperature does not affect

both the volume and mass of the EPS cubes up to a temperature of 70°C.

However, it is seen that under temperatures of 80°C or higher the EPS cubes

experienced volumetric changes. Note that up to 80° C the reduction in size was

relatively uniform and hence the cubical shape was always retained (Figure 4.4).

This could be because the EPS contains nearly 98% voids by volume filled with

gas (Horvath, 1995). The gas entrapped in the voids of EPS beads would be stable

up to 70°C but starts to escape at temperatures greater than 70°C. This would

transform the EPS bead into a polystyrene bead.

Chapter 4

72

Even though the size and volume of the cubes were changed at a temperature of

80°C or higher (Figure 4.4), the mass remained unaltered. This is an important

observation, since for calculating the moisture contents and subsequently the dry

unit weight of the soil-EPS mix; the sample has to be kept in the oven at 105°C.

Initial side dimension (i) 30 mm (ii) 20 mm (iii) 10 mm

Figure 4.4 Reduction in size of specimens before and after heating at 80°C. 4.3 Dredged soil from Port of Brisbane

The characteristics of the dredged soil, tested as per the relevant Australian

Standards are summarised in the Table 4.3, which are in agreement with most

marine soils found around the world (Table 4.1). The compaction curves

(Standard and modified) for the dredged soil are shown Figure 4.5. This

compaction standard was adopted for all the tests in this scoping study.

Standard compaction

Modified compaction

8

10

12

14

16

18

0 10 20 30 40 50 60

Moisture content, %

Dry

uni

t wei

ght,

kN/m

3

Figure 4.5 Compaction curves for the dredged soil tested.

Chapter 4

73

Table 4.3 Characteristics of the dredged soil.

4.4 Preparation of dredged soil and EPS mix

For performing tests with dredged soil-EPS mix, the specimens were prepared in

the following mix procedure. As the natural moisture content of the dredged soils

was 80%, it was brought down to slightly below the optimum moisture content by

air drying. Subsequently, tap water at room temperature was added to the soil to

bring the moisture content to the desired values. Then these samples were cured

for 7 days in a sealed zipper bag. Thereafter, the recycled EPS beads were mixed

to this moist soil in different proportions using a bench top Hobart mixer. A

photograph of the dredged soil at 45% moisture with 2% of recycled EPS beads

before compaction is shown in Figure 4.6.

Soil Property Standard method Value

Particle density AS 1289.3.5.1 - 1995 2.65

Natural moisture content,% AS 1289.2.1.1 – 1992

80

Organic matter content, % AS 1289.4.1.1 - 1997 8

Atterberg Limits Liquid limit, % Plastic limit, % Plasticity Index, % Linear Shrinkage, %

AS 1289.3.1.1 – 1995/ Amdt. 1 -1998 AS 1289.3.2.1 – 1995

119 38 81 26

Particle size distribution Clay,% Silt, %

AS 1289.3.6.3 - 2003 57 28

Compaction characteristics Maximum dry unit weight, kN/m3 Optimum moisture content, %

AS 1289.5.1.1 - 2003

12.85 39

Chapter 4

74

Figure 4.6 Dredged soil – EPS beads composite before compaction

at 45% moisture content.

4.5 Optimum mix proportion of Soil-EPS mixes

For compaction purposes, two factors were considered in this study. The first

factor was the optimum moisture content of the dredged soil at which the

maximum dry unit weight was achieved and the second factor was the maximum

amount of EPS beads that could be added at this optimum content so that EPS

could be mixed uniformly with the dredged soil.

In some of the earlier studies (Miki, 1996; Okumura et al., 2000), the mixing rate

of EPS beads with soil was based on volume. However, the mixing rate used in

the present study was defined as the mass ratio of EPS beads to dry soil as used by

Minegashi et al. (2002). This method was adopted because volumetric

proportioning is affected by the size and gradation of EPS beads. This problem

can be avoided if proportioning is done on mass basis. This proportioning method

was also used for mixing fibres with soils (Maher and Gray, 1990; Ziegler et al.,

1998; Miller and Rifai, 2004).

At the optimum moisture content (39%), recycled EPS beads were mixed to the

dredged soil in proportions of 0.5%, 1.0% and 1.5%. However, at 1.5% proportion

it was observed that the beads were not mixing homogeneously with the soil.

Upon subsequent mixing at lower EPS contents, it was observed that the EPS

beads content had to be limited to about 1.25% of the dry soil mass to avoid

Chapter 4

75

segregation and to have uniformity in the mix. Figure 4.7 shows the soil-EPS mix

at OMC at different EPS ratios.

(a) (b) (c)

Figure 4.7 Cross section of Soil-EPS mix at OMC (39%) (a) 0.5% EPS, (b) 1.0 % EPS and (c) 1.25% EPS.

As mentioned earlier, one of the aims in this scoping study is to use the recycled

EPS beads to the maximum extent in geotechnical lightweight backfill

applications to improve their recycling rate. Hence, compaction tests were

performed to investigate the possibility of increasing the EPS content beyond

1.25%. For each compaction specimen, the moisture content was increased in

increments of approximately 5%. It was observed that for EPS content greater

than 1.25%, compaction would have to be done at moisture content of 45% to

produce a uniform mix. However, the maximum percent of EPS that could be

added at this moisture content was 2%, beyond which the EPS beads resisted

densification and segregation could be noticed. Typical cross sections of

composites prepared with moisture content of 45% are shown in Figure 4.8.

To further increase the EPS content, the moisture content of dredged soil was

increased to 50%. In this case, a maximum of 3% of EPS could be added while

maintaining the uniform and homogeneous mix conditions. The resulting cross

sections are shown in Figure 4.9. This indicates that in terms of EPS inclusion to

the soil, the maximum quantity that could be added is influenced by the moisture

content of the soil. However, it should be noted that the higher the moisture

content, the lesser the workability of the soil-EPS mix would be. Hence, in

Chapter 4

76

situations where strength and settlement are not a concern, EPS beads can be

added to maximise their use as long as a homogeneous mix can be attained with a

workable moisture content.

(a) (b)

Figure 4.8 Cross section of Soil-EPS mix at 45% water content (a) 1% of EPS and (b) 2% EPS.

(a) (b) (c)

Figure 4.9 Cross section of Soil-EPS mix at 50% water content (a) 1% of EPS, (b) 2% EPS and (c) 3% of EPS.

4.6 Compaction properties of soil-EPS mixes

The wet unit weights of the soil-EPS mixes at different percentage of EPS, tested

as per AS 1289.5.1.1 -1992, are shown in Table 4.4. It is noted from this table that

the addition of EPS beads reduces the wet unit weight of the composite depending

on the quantity of EPS added. This is because of the lightweight nature of EPS

beads. In addition, the reduction varies with moisture content and percent EPS.

Chapter 4

77

The variation of the wet unit weight with EPS inclusion to the dredged soil is

shown in the Figures 4.10 through 4.12. From the Figures 4.10 and 4.11, it can be

observed that variation is linear at lower moisture contents and becomes

curvilinear at higher moisture contents as shown in Figure 4.12.

Figure 4.13 demonstrates that the change in the wet unit weight was influenced by

both the percentage of EPS and the initial water content of the soil at which the

compaction was carried out. The reduction in wet unit weight was more

pronounced with increased EPS content than increased moisture content. Overall,

in percentage terms, the reduction in wet unit weight caused by EPS inclusion was

from 13.97% (for soil at 39% moisture content with 0.5% EPS) to 32.51% (for

soil at 50% moisture content with 3% EPS).

Table 4.4 Wet unit weights of Soil-EPS mixes at different mix proportions.

Moisture content (%)

EPS (%)

Soil-EPS wet unit weight

(kN/m3) 39 0.0 17.75

39 0.5 16.23

39 1.0 15.27

39 1.25 14.64

45 0.0 16.96

45 1.0 14.81

45 2.0 13.29

50 0.0 16.67

50 1.0 13.62

50 2.0 12.16

50 3.0 11.25

It should be noted that higher the moisture content, the higher the post drying

shrinkage of the composite. Furthermore, mixes with higher moisture content

values may require higher stabiliser (cement, lime) content to achieve the required

strength. Thus, it would be desirable to prepare mixes at or near the OMC for

optimisation of the mix proportion. In addition, with 3% EPS at 50% moisture

content, it was observed that the compaction was not effective in the sense that the

soil was too soft and sticky to compact. Hence, the mix proportion subsequently

adopted for this scoping study was 2% EPS at 45% moisture content. It should be

Chapter 4

78

noted that for controlling the expansive behaviour of the soil, the addition of EPS

must be maximised, not only because this would influence the swell-shrink

characteristics of the soil-EPS mixes, but also because it would be desirable to

increase the use of waste EPS in geotechnical applications.

In an attempt to find the OMC for a given mix of soil and EPS, compaction

specimens were prepared at moisture contents below and above the OMC of the

soil. It was observed that at a moisture content below the OMC of the soil, the

homogeneity of the mix could not be attained without reducing the EPS content

primarily because of the resistance offered by the EPS to densification.


0

4

8

12

16

20

0 0.5 1 1.5

EPS, %

Wet

un

it w

eigh

t, kN

/m3

Figure 4.10 Variation of wet unit weight with EPS at OMC (moisture content = 39%).

Chapter 4

79


0

4

8

12

16

20

0 0.5 1 1.5 2 2.5

EPS, %

Wet

uni

t wei

ght,

kN/m

3

Figure 4.11 Variation of wet unit weight with EPS at 45% moisture content.


0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3 3.5

EPS, %

Wet

uni

t wei

ght,

kN/m

3

Figure 4.12 Variation of wet unit weight with EPS at 50% moisture content.

Chapter 4

80

39% moisture content



10

11

12

13

14

15

16

17

18

19

0 0.5 1 1.5 2 2.5 3 3.5

EPS, %

Wet

uni

t wei

ght,

kN/m

3

Figure 4.13 Variation of wet unit weight with percent EPS and moulding moisture

content. 4.7 Strength behaviour of soil-EPS mixes

Since moulding moisture content has a significant effect on the amount of EPS

that can be added to and workability of the mix, it was decided to study how these

factors would influence the strength characteristics as a construction fill material,

with and without any chemical stabilisers. For that purpose, the California

Bearing Ratio, Unconfined Compressive Strength and drained direct shear tests

were conducted.

As the soil contains high percentage of clay (Table 4.3), hydrated lime was used

in some test specimens as a stabilising agent to improve swelling and strength

characteristics. In this case, the available lime represents the total free lime (CaO)

content in the hydrated lime. This is the reactive constituent and is normally used

as a means of evaluating the concentration of lime (Little, 1995). The available

lime index, as per AS 4489.6.1 -1997, was found to be 68%.

Lime and EPS were added in the required proportions to the moist soil sample

(see Section 4.4) and another 2% of water was added to compensate for the water

lost through hydration of lime. The mixes were allowed to mellow for 2 days by

Chapter 4

81

placing them in polythene bags prior to compaction. The specimens were cured

under accelerated conditions of 48.9° C for 48 hours to replicate the curing

conditions of 22°C for 28 days as used by Thompson (1970).

Past studies indicated that the effect of stabilisation varies with the available lime.

The lesser the available lime in the sample, the lesser the strength attained by the

composite. It should be noted that the use of lime in soil has a limitation; it cannot

help increasing the strength of the composite beyond a certain maximum amount.

4.7.1 California Bearing Ratio

In the design of base and subbase material for pavement, the California Bearing

Ratio (CBR) value is widely used, which gives an indication of the soil strength

and bearing capacity under controlled density and moisture conditions. In the

present investigation, as the soil-EPS mixes was originally intended to be used as

a controlled fill for pavements and embankments to increase their recycling rate,

the CBR is therefore an appropriate indicator test used to evaluate the strength of

soils for these applications. The CBR tests were performed both in soaked and

unsoaked conditions as per AS 1289.6.1.1 – 1998.

4.7.1.1 Unsoaked conditions

Table 4.5 shows the values of CBR at different moisture contents and also at

different EPS and lime contents. No correction was required for the CBR curves

shown in Figure 4.14. The last three CBR values were measured at the 5.0 mm

penetration since these values were higher than those of the 2.5 mm penetration;

however, the remaining CBR values were obtained at 2.5 mm penetration.

The addition of EPS lowered the unit weight of the soil and decreased the CBR

considerably. The addition of lime overcame this problem by increasing the

strength at the reduced unit weight. In the present study, CBR increased with an

increase in lime content up to 5%, thereafter additional lime caused a reduction in

the CBR values. This behaviour is consistent with the fact that the addition of

lime may not correspond with a direct increase of the CBR (Bell, 1996).

Chapter 4

82

The CBR values of the soil at OMC and at 45% were 5 % and 1 %, respectively.

The addition of 2% EPS to soil at 45% moisture content, which was identified

earlier as the optimum EPS mix proportion, had little effect on the already low

CBR. The use of lime in this case would be necessary to increase the CBR, so that

the soil-EPS mix can be used as a lightweight embankment material. Note that

with 30% reduction in the wet unit weight by using 2% EPS (Table 4.4), the

potential embankment settlement would be significantly reduced.

Unsoaked

0

0.5

1

1.5

2

2.5

0 2 4 6 8 10 12 14Penetration of piston (mm)

Load

on

pist

on (k

N)

at OMC (0% EPS & 0% lime)at 45% MC (0% EPS & 0% lime)at 45% MC (2% EPS & 0% lime)at 45% MC (2% EPS & 3% lime)at 45% MC (2% EPS & 5% lime)at 45% MC (2% EPS & 7% lime)

Figure 4.14 Unsoaked CBR curves.

Table 4.5 CBR Values of the soil-EPS mixes.

Moulding Moisture Content

(%)

Lime (%)

EPS (%)

Unsoaked CBR (%)

Soaked CBR (%)

39* 0 0 5.0 4.0

45 0 0 1.0 1.5

45 0 2 1.5 1.5

45 3 2 6.0 1.5

45 5 2 10.0 1.5

45 7 2 8.0 1.0

* Optimum moisture content

Chapter 4

83

4.7.1.2 Soaked conditions

To predict the strength of the composite under the worst possible scenario and

also to observe its swelling potential, soaked CBR tests were performed. The

specimens were soaked for 4 days under a surcharge load of 4.5 kg and the

swelling and soaked CBR values were calculated. Table 4.5 shows the soaked

CBR values. For these cases too, there is no need for correction (Figure 4.15). It is

seen that the soaked CBR values of specimens prepared at 45% moisture content

are lower than the value for samples prepared at OMC irrespective of EPS and

lime content.

The above results show that with an increase in moisture content and the

subsequent saturation of specimens, considerable reduction in CBR and strength

of the composite occurred. Even though lime was added as a stabiliser, it did not

cause any improvement in soaked CBR. This could be attributed to the sulphate

content in dredged soil which led to ettringite formation (see Section 4.8.1).

Similar result was also evident at 7% lime content where there was a reduction in

CBR form 1.5% to 1.0%.

Soaked

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14

Penetration of piston (mm)

Load

on

pist

on (k

N)

at OMC (0% EPS & 0% Lime)at 45% MC (0% EPS & 0% lime)at 45% MC (2% EPS & 0% lime)at 45% MC (2% EPS & 3% lime)at 45% MC (2% EPS & 5% lime)at 45% MC (2% EPS & 7% lime)

Figure 4.15 Soaked CBR curves.

Chapter 4

84

4.7.2 Unconfined compressive strength

The unconfined compressive strength values for specimens with and without EPS

(tests conducted as per AS 1141.51–1996) are shown in Table 4.6. It is seen that

although the strength of the lime treated soil-EPS mixes cannot be as high as those

of the lime-treated soil at the same lime content, it is much higher than that of the

original soil. Note that the results confirm that the addition of lime does not

necessarily increase the strength proportionally in agreement with the previous

studies (Bell, 1996).

Table 4.6 Unconfined compressive strength of soil-EPS mixes.

Moulding moisture

content, % Lime, % EPS, %

Unconfined compressive

strength, kPa 39 0 0 80.0

45 0 0 58.3

45 3 0 1710.0

45 5 0 1754.8

45 7 0 1197.9

45 3 2 247.0

45 5 2 383.0

45 7 2 295.0

Figures 4.16, 4.17 and 4.18 show the stress-strain curves at different lime contents

of 3%, 5% and 7% respectively, with and without EPS. The addition of EPS

makes the mix less brittle and takes more strain to failure than the lime treated

soil. Even though the strength is not comparable to the lime stabilised soil, it

shows promise as a lightweight fill/embankment material behind a retaining wall

or bridge abutment where relatively large movements may be anticipated.

Chapter 4

85

3% lime

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14Axial strain, %

Axi

al s

tres

s, k

Pa

with 2% EPSwithout EPS

Figure 4.16 Stress-strain curve of a composite with 3% lime.

5% lime

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14Axial strain, %

Axi

al s

tres

s, k

Pa


Figure 4.17 Stress –strain curve of a composite with 5% lime.

Chapter 4

86

7% lime

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14Axial strain, %

Axi

al s

tres

s, k

Pa


Figure 4.18 Stress – strain curve of a composite with 7% lime.

4.7.3 Drained shear strength

Slow drained shear box tests were carried out on 60 mm × 60 mm composite

specimens. The moisture content of the specimens was 45% and EPS content was

2%. The corresponding wet unit weight of the specimen was 13.29 kN/m3. The

typical shear box results are shown in Figure 4.19, showing the variation of shear

strength with shear displacement.

The vertical displacements are also plotted against the shear displacement in

Figure 4.20. Under a 50 kPa pressure, the Soil-EPS mix compresses slightly with

increasing shear displacement but subsequent shear displacements causes dilation.

This effect is more pronounced at higher normal stress levels (100 and 150 kPa)

as shown in Figure 4.20.

The shear strength and corresponding normal stresses are plotted in Figure 4.21.

The shear strength envelope is fitted as the best fitting line which gives the

following internal friction angle, φ’, and apparent cohesion, c’.

φ’ = 21.9°

c’= 14.1 kPa

Chapter 4

87

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8

Shear displacement, mm

She

ar S

tres

s, k

Pa

50kPa100kPa150kPa

Figure 4.19 Typical shear box test on Soil-EPS mix at different normal stress levels.

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0 1 2 3 4 5 6 7 8Shear displacement, mm

Ver

tical

dis

plac

emen

t, m

m

50kPa100 kPa150 kPa

Figure 4.20 Vertical displacement of the Soil-EPS mix in shear box test at different

normal stress levels.

Chapter 4

88

0

25

50

75

100

125

150

175

0 25 50 75 100 125 150 175

Normal Stress, kPa

She

ar S

tres

s, k

Pa

Figure 4.21 Shear strength of Soil-EPS mix.

4.8 Swell – shrink studies

Dredged soil being a highly plastic clay, if used as construction fill, would

obviously experience swelling and shrinkage movements. Hence, the addition of

EPS in controlling those movements was investigated in keeping with main focus

of this study.

4.8.1 Swelling

The swelling tests were conducted on the soaked CBR specimens in accordance

with AS1289.6.1.1-1998, while simultaneously soaking the specimens for the

soaked CBR test. The specimens were soaked for 4 days by applying surcharge

loading of 4.5 kg. The results from soil specimens moulded with 45% moisture

(6% on the wet side of the optimum) displayed similar trends as discussed by

Chen, (1988), Nelson and Miller (1992). The swelling is generally minimal (Table

4.7), and particularly insignificant for the lime-stabilised soil up to 5% lime

content. However, at 7% lime content, swelling of 1% was observed. This could

be attributed to the formation of ettringite. The dredged soil contains soluble

Chapter 4

89

sulphates, which, in high enough concentration, can interfere with pozzolonic

reaction. The extent to which ettringite may form depends upon the availability of

silica, alumina and calcium ions (Bhattacharja et al., 2003). In a study, O’Sullivan

et al., (2005) estimated that the sulphate concentration in the dredged soil from

Port of Brisbane to be in the range of approximately 10 mg/kg to 70 mg/kg

depending on the depth of excavation.

When soils with soluble sulphates are treated with any calcium based stabilisers,

such as lime in the present case, they form calcium-suphate-aluminate-hydrates

which are harmful because of the expansion and potential swelling pressure that

results from their formation (Little, 1995). According to Little (1995), the

reactions can lie dormant until water carries soluble sulphates from the soil to the

mixed stabilisers. The water will then hydrate the lime, increase the pH of the clay

which will release alumina in the sulphate environment. In the present case, as the

lime was in low proportions, the reaction would be somewhat limited for 3% and

5% lime content. The prescribed test duration was 4 days; however, had the test

duration increased it would have shown a further increase in swelling.

Furthermore, for a given volume of SWEPS mix, the addition of EPS beads

replaces the soil volume correspondingly. Therefore, the soil volume decreases for

an increase in EPS volume for a given soil-EPS mix. Consequently, the added

lime will react better with the less amount of soil, and start showing swelling

tendency even in small quantities with increased EPS contents (Table 4.3).

Hence, with EPS content of 2%, samples of soil-EPS mix produced high swell

values in the order of 3%.

Further to the above, the dredged soil contains organic materials. The addition of

lime oxidises the organic matter such that the available lime for stabilisation is

reduced. As explained earlier, for the ettringite to form, there should be an

increase in the pH of the clay. At lower lime contents, the pH may not increase to

the required levels. However, at 7% lime content and also with the addition of

EPS to the dredged soil, the pH increases to the required level for releasing the

alumina in the sulphate environment, and thus causes swelling as presented in

Table 4.7.

Chapter 4

90

Table 4.7 Swelling and shrinkage of the soil – EPS mixes.

Moulding Moisture Content (%)

Lime (%)

EPS (%)

Swelling (%)

Shrinkage (%)

39* 0 0 1.00 23.0

45 0 0 0.00 25.0

45 3 0 0.00 11.0

45 5 0 0.00 11.0

45 7 0 1.00 11.0

45 3 2 3.00 7.5

45 5 2 3.00 7.5

45 7 2 3.00 7.5

4.8.2 Shrinkage

The shrinkage test was conducted as per AS 1289.7.1.1 - 2003. The specimen was

prepared in a three-part split mould with 100 mm diameter and 200 mm height at

the designated moisture content using a specific stabiliser content. After

compacting, two drawing pins were fixed on the side of the cylindrical specimen.

The specimen was then air dried for 4 hours and subsequently oven dried at

48.5°C. The change in the distance between these two pins was measured using a

pair of Vernier Callipers until the shrinkage ceased. Table 4.7 shows the shrinkage

of specimens of soil and soil-EPS mixes.

It was observed that, evidently, with an increase in moisture content there is an

increase in shrinkage of the soil. For 0% EPS content and 0% lime content at

optimum moisture content, the shrinkage is 23%; whereas for the same soil with

the same lime and EPS content but at a moulding moisture content of 45%, the

shrinkage was 25%.

Furthermore, at a moulding moisture content of 45%, the shrinkage reduces from

25% to 7.5% with addition of lime and EPS to the soil. Unlike swelling, there is

no influence of soluble sulphates in the case of shrinkage due to the drying of

water from the soil-EPS mix.

Chapter 4

91

4.9 Need for further studies with reconstituted expansive soils

Scoping studies with dredged soil and recycled EPS beads is discussed in this

chapter. From these it can be observed that there is a limit on the amount of EPS

beads that can be added to a soil, which is controlled by the moulding moisture

content. EPS inclusion decreases the CBR or UCS values of soils. If lime is

added, the strength of the soil-EPS mix can be improved.

Furthermore, the increase in swelling with an increase in EPS content in this

scoping study seemed to suggest that hypothesis postulated at the beginning of the

thesis was wrong (that EPS beads can control the swell-shrink behaviour of

expansive soils through their elastic nature). However, this could be due to the

higher moisture content which was five percent above the OMC and also due to

the presence of sulphates in the dredged soil. The higher moisture content aids in

the dissolution of sulphate with lime.

In addition to the problem caused by the presence of sulphates, the other

limitations which restricted the use of dredged soil in this study:

1. The present dredged soil has a plasticity index of 81%, which is rather an

extreme case when compared with the naturally occurring expansive soils

and other dredged soils, whose plasticity indices vary from 25 to 50% as

shown in Table 4.1 and Table 4.1, respectively. Such as highly plastic clay

would be difficult to compact.

2. The influence of recycled EPS on swell-shrink behaviour cannot be

studied over a range of PI values from the dredged soil alone. While the

dredged soil could be mixed with other material(s) to alter its plasticity,

such as procedure would be difficult to perform.

Considering the above, it was considered that further studies had to be conducted

using artificially reconstituted soils with no reactive compounds.

Chapter 4

92

4.10 Summary

The influence of recycled EPS beads on the different characteristics of a soil was

investigated in this preliminary scoping study with a dredged soil from Port of

Brisbane. From this study it was observed that the amount of EPS that can be

mixed with the soil depends on the moulding moisture content. In addition, it was

found that EPS inclusion reduced the strength of the soil but showed potential for

reducing drying shrinkage. Even though it was not observed in this scoping study,

reduction in shrinkage should also indicate the potential of EPS beads in reducing

swelling. The presence of sulphates in dredged soil hindered the effect of EPS in

reducing swelling which necessitated further studies with reconstituted expansive

soils.

Chapter 5 describes the selection of reconstituted expansive soils consisting of

sand and sodium bentonite. In this case, sand acts as an inert material and

bentonite generates swelling in the composite up on saturation. By using these

reconstituted soils, the influence of EPS inclusion on the swell-shrink

characteristics can be studied systematically.

93

CHAPTER 5 - SAND - BENTONITE (SB) MIXES ___________________________________________________________

A comprehensive laboratory testing program was performed to characterise the

basic properties of reconstituted soils (Sand-Bentonite or SB mixes) to be used as

test soils for mixing EPS beads in this study. The results served two purposes: (a)

identify and classify the test soils, and (b) obtain essential information and

parameters for swelling and related tests.

Based on the findings of preliminary scoping study discussed in Chapter 4,

potentially expansive soil was prepared in the laboratory using fine sand and

sodium rich bentonite. The basic material properties, the testing details and

corresponding results of SB mixes are presented in this chapter.

The SB mixes that will be discussed in the ensuing chapters are referred to as

SB16, SB24 and SB32; this chapter describes the manufacturing process and

general properties of these reconstituted soils. In addition, methods for preparing

lime stabilised SB mixes and Soil with EPS (SWEPS) mixes are also described.

5.1 SB mix as a model material for expansive soil

To obtain soils of differing Atterberg limits for experimental purposes, it is a

common practice to mix bentonite with fine sand or kaolinite or other natural

soils. This method has been followed by various researchers. Seed et al. (1964)

reported the use of such mixed soils in order to establish relationship between the

plasticity index and the percent of the clay size fractions. Furthermore,

Sivapulliah and Sridharan (1985), Pandian et al. (1995), Ziegler et al. (1998) and

Sridharan et al. (1999) also used such mixtures to obtain a wide range of plasticity

indices for their studies. Hence, in the present investigation, fine riverine sand

and bentonite powder were mixed in different fractions to produce potentially

expansive soils as test soils for performing swelling, shrinkage and desiccation

studies.

Furthermore, the SB mixes were particularly selected for the present research

because they are often used as a hydraulic barrier in landfill applications (liner and

cover materials) and also in nuclear waste disposal applications as buffer

Chapter 5

94

materials (Kenny et al., 1992; Van Ree et al., 1992; Pandian et al., 1995;

deMagistris et al., 1998; Chapuis, 2002; Chalermyanont and Arrykul, 2005). The

behaviour of SB mixes has been studied by many researchers. Published data are

generally available for comparison purposes and to provide information for the

present study.

The content of bentonite to be mixed with local soils or sand to use as a liner or

cover is generally limited to 20% in order to limit the swelling and shrinkage of

the mix (Kenny et al., 1992; Rowe, 2001). With uncontrolled swell-shrink, cracks

can easily develop in landfill liners or covers and cause leaks that increase the

leachate rates.

With the use of artificially constituted SB mixes as test soils, the spatial variability

that normally occurs in natural expansive soils can be eliminated to a greater

extent. For instance, in scoping studies (Chapter 4), it was observed that the

sulphate present in the dredged soil affected the actual swelling mechanisms with

the addition of lime as stabilisers.

In addition to obtaining consistent properties, the use of SB mixes allows the

severity of swelling and shrinkage potential to be designed by altering the

percentage of bentonite fraction, thus the effect of EPS beads additions can be

studied for soils with different plasticity values.

Before finalising reconstituted mix proportions for the artificial expansive soils, a

survey of the published literature with regards to variations in index properties of

expansive soils was undertaken. The Atterberg limits of expansive soils at the

different locations in different countries are given in Table 5.1. Upon plotting a

graph (Figure 5.1) with the location number on x-axis and corresponding

plasticity index (PI) on y-axis, it was observed that one third of locations fall in

the PI range of less than 26%, middle one third fall in the PI range of 26-38% and

last one third of locations fall in the PI range of 38-56%. Based on this criterion, it

was decided to prepare three reconstituted soils using sand and bentonite to

produce clays with intermediate, high, and very high plasticity values.

Chapter 5

95

Table 5.1 Index properties of expansive soils from different locations around the world. Location number and name Country LL Pl PI

1 Diao-Nan Irrigation project, Sector C14

China 40.5 22.5 18.0

2 Nanayng (brown)10 China 42.0 22 20.0 3 Hefei, Soil212 China 42.5 21.7 20.8 4 Diao-Nan Irrigation

project, Sector A14 China 46.1 25.3 20.8

5 Nanyang(Yellow)10 China 46.0 25.0 21.0 6 Diao-Nan Irrigation

project, Sector B14 China 52.9 31.9 21.0

7 Yeldahri1 India 68.0 46.2 21.8 8 Al-Khod17 Oman 56.8 34.9 21.9 9 Oltu deposits,

soil 216 Northeast of Turkey

60.0 38.0 22.0

10 Irbid, soil A18 Northern Jordan

35.0 11.0 22.0

11 Arlington8 USA 44.0 22.0 22.0 12 Oltu deposits


65.0 42.0 23.0

13 Tuzla4 Cyprus 48.4 25.0 23.4 14 Hefei, Soil112 China 49.9 26.2 23.7 15 Nasik1 India 72.8 48.2 24.6 16 Nanyang13 China 48.9 23.3 25.6 17 Nanyang(gray)10 China 53.0 27.0 26.0 18 Lousiana6 USA 46.0 19.0 27.0 19 Ankang13 China 50.8 23.8 27.0 20 Oltu deposits,


62.0 35.0 27.0

21 Sholapur1 India 69.2 41.9 27.3 22 Mianxi13 China 51.4 23.5 27.9 23 Xixiang13 China 53.0 24.9 28.1 24 Sidheswar1 India 70.3 41.0 28.4 25 Brisbane21 Australia 55.0 26.0 29.0 26 Alamatti1 India 59.8 30.4 29.4 27 Oltu deposits,


65.0 35.0 30.0

28 Belgaum soil 22 India 55.0 25.0 30.0 29 Ankang13 China 58.3 28.0 30.3 30 Nanyang5 Singapore 58.3 26.5 31.8 31 Dallas- Fort Worth,

Texas8 USA 50.0 18.0 32.0

32 Amravati1 India 81.0 47.0 34.0 33 Irbid, soil E18 Northern

Jordan 62.0 28.0 34.0

34 Nile river11 Egypt 60.0 23.0 37.0 35 Mesquite, Texas15 USA 60.0 23.0 37.0 36 Irbid, soil D18 Northern

Jordan 75.0 38.0 37.0

37 Ravenhall, Melbourne, Soil 120

Australia 78.0 41.0 37.0

39 Yaqualing13 China 72.9 34.9 38.0 40 Francistown3 Botswana 65.0 27.0 38.0

Chapter 5

96

Location number and name Country LL Pl PI 41 Echuca, Victoria19 Australia 63.0 25.0 38.0 42 Poona1 India 81.5 43.2 38.3 43 Malaprabha1 India 74.0 34.0 40.0 44 Quail creek, Arlington9 USA 69.0 28.0 41.0 45 South cooper estate East,

Arlington9 USA 71.0 29.0 42.0

46 Nasr City11 Egypt 76.0 34.0 42.0 47 Werribee, Victoria19 Australia 74.0 32.0 42.0 48 Walnut creek, Arlington9 USA 69.0 43.0 49 South cooper estate West,

Arlington9 USA 74.0 29.0 45.0

50 Degirmenlik4 Cyprus 67.8 22.2 45.6 51 Belgaum soil 12 India 65.0 19.0 46.0 52 San Antonio7 USA 73.0 27.0 46.0 53 Bryan, Texas15 USA 68.0 20.0 48.0 54 Nasr City11 Egypt 80.0 28.0 52.0 55 Vijayawada1 India 91.8 38.3 53.5 56 Irving7 USA 82.0 27.0 55.0 57 Ravenhall, Melbourne,

Soil 220 Australia 103.0 47.0 56.0

Sources: 1Katti and Katti (1994); 2Rao et al. (2001); 3Sahu (2001); 4Nalbantoglu and Gucbilmez (2002); 6Puppala et al.(1996); 7Puppala and Musenda (2000); 8Punthutaecha et al. (2006); 9Puppala et al. (2003); 10Bao and Liu (1988); 11El-Sohby et al. (1988) ; 12Fan and Yang (1988) ; 13Li and Zhao (1988) ; 14Liu et al. (1988); 15Rauch et al. (2002); 16Kalkan and Akbulut(2004); 17Basma et al. (1998); 18Al-Homoud et al. (1995); 19Kodikara et al. (2002); 20Jayasekara and Mohajerani (2001); 21Jones et al. (2001)

1/3 of locations

1/3 of locations

1/3 of locations

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Location number with reference to Table 5.1

Pla

stic

ity in

dex,

%

Figure 5.1 Variation of plasticity index at different locations around the world.

Chapter 5

97

5.2 Material properties

5.2.1 Fine Sand

Commercially available fine white sand labelled as W9 supplied by Riversands

Pty Ltd., Brisbane was used. The sand is sub-angular silica sand and classified as

poorly graded clean fine sand (SP) according to Unified Soil Classification

System (AS 1726, 1993). Its specific gravity is 2.65. Greater than 95 percent of

the sand particles passes through no. 30 sieve (0.420 mm) and less than 5 percent

passes the no.200 sieve (0.074 mm).The particle size distribution curve for sand is

plotted in Figure 5.2. The uniformity coefficient Cu (= D60/D10), the effective

diameter D10 and the mean diameter D50 of the sand are 1.53, 0.17 mm and 0.24

mm, respectively.

0

20

40

60

80

100

0.01 0.1 1 10Particle size, mm

Per

cen

tage

fin

er

Figure 5.2 Particle size distribution curve for sand.

5.2.2 Bentonite

Bentonite, a very highly plastic and swelling clay mineral, refers to any material

that is primarily composed of the montmorillonite group of minerals formed by

the chemical weathering of volcanic ash and whose physical properties are

dictated by the montmorillonite minerals (Grim and Guven, 1978). Basically,

bentonite is a sodium montmorillonite clay in which mica-like layers are bonded

together by sodium ions. Smectite is the family name of montmorillonite and

bentonite (Tsai, 1993). According to Mitchell and Soga (2005), bentonite is a

highly colloidal and expansive clay that may have a liquid limit of 500 percent or

more. Characteristics of montmorillonite minerals include large cation exchange

Chapter 5

98

capacity, large specific surface area, high swelling potential and low hydraulic

conductivity to water (Gleason et al., 1997)

In the current study, commercially available powdered natural sodium-rich

bentonite supplied by Unimin Australia limited, Brisbane was used. This

bentonite came from Miles, which is 350 kilometres west of Brisbane,

Queensland, Australia.

The physical properties of the bentonite are shown in the Table 5.2. The

generalised X-ray diffraction plot and mineralogy of the bentonite used in the

present study are shown in Figure 5.3 and Table 5.3 respectively (Gates et al.,

2002).

Table 5.2 Properties of bentonite.

Trade name Trubond

Source Miles, Queensland, Australia

Type Sodium bentonite Retained on 75 �m (Wet screen) Passing 2 �m (XRD Analysis)

2% 80%

Bulk density 0.9 t/m3

Liquid limit 400%

Plastic Limit 41%

Moisture content (as supplied) 11%

Cation exchange capacity 85 meq/ 100 g

Table 5.3 Mineralogy of Miles bentonite (Gates et al., 2002).

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Chapter 5

99

Figure 5.3 X-ray diffraction plot of the bentonite used in the study. S = Smectite, M= Mica, S/M = Smectite/ Mica, Q= Quartz, C = Cristobalite / opal, F= Feldspar

(Gates et al., 2002).

5.3 SB mix preparation

The designated amount of bentonite powder was added to the dry sand by dry

weight basis, e.g. 10% bentonite content refers to addition of dry bentonite

amounting 10% of the weight of dry sand. These two materials were then

thoroughly mixed by hand several times until a fairly uniform and consistent

mixture was obtained. Distilled water was subsequently added in the required

quantity in increments and the mixture was worked by hand for about 15 minutes.

Based on visual observation of the mixture and upon satisfying that the moisture

had been distributed evenly all over the mixture, the samples were then sealed into

plastic containers and placed in a humid chamber for at least 14 days to reach

moisture equilibrium before being subjected to various tests.

5.4 Atterberg limits

As mentioned earlier, in preparing reconstituted soils, the aim was to obtain soils

potentially with plasticity index (PI) in the range of 20 to 35% (corresponding to

low PI), 35 to 50% (corresponding to intermediate PI) and >50% (corresponding

to high PI). For that purpose Atterberg limit tests were conducted on four different

preliminary mixtures prepared by adding dry bentonite of 10%, 20%, 30% and

40% of the dry mass of sand. These tests were performed according to

AS1289.3.1.1 – 1995 and AS1289.3.2.1-1995 for liquid limit and plastic limits,

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Chapter 5

100

respectively. The variations of the liquid limit and plastic limit are shown in

Figure 5.4.

Liquid limit

Plastic limit

0

50

100

150

200

250

300

350

400

450

0 20 40 60 80 100Bentonite. %

Liqu

id li

mit,

Pla

stic

lim

it, %

Figure 5.4 Liquid limits and plastic limits for sand-bentonite mixes.

It is well known that clay particles, due to their very large specific surface area,

form a cohesive membrane around coarser particles. This prevents direct contact

among coarser particles, i.e. the coarser particles become embedded in a matrix

provided by the clay particles (Pandian et al., 1995).

Seed et al. (1964) mentioned that the liquid and plastic limits of a soil are

primarily controlled by its clay content. Therefore, the increases in these indices

are expected as clay content increases due to the addition of bentonite. However,

the influence of bentonite, as shown in Figure 5.4, is more significant on the

liquid limit than the plastic limit. Liquid limit shows an approximately curvilinear

increment whereas plastic limit shows a linear increment. This is in agreement

with the results reported by deMagistris (1998) and Montanez (2002).

In the current study, the liquid limit increases from 33 to 84% with an increase in

bentonite content from 0% to 40%. While Pandian et al. (1995) showed a linear

relationship for sand-bentonite mixtures, the liquid limit variation shown in Figure

Chapter 5

101

5.4 exhibits a non-linear trend. These differences may be attributed to the method

of proportioning sand and bentonite for the mixes. Pandian et al. (1995) prepared

the mix by adding bentonite into the mix to replace the same quantity of sand.

However, in the current study, bentonite was added by the dry weight of sand, i.e.,

for a fixed quantity of sand, different bentonite contents were added.

With regards to the variation of plasticity with bentonite content, Montanez

(2002) observed that for a uniform sand, the plastic limit shows a slight and

almost negligible increase. The same were observed in the current research. That

is the plastic limit increased slightly from 17% to 24% with an increase in

bentonite content from 10% to 40%.

By systematically analysing the Atterberg limits of these preliminary mixtures,

bentonite contents of 16%, 24% and 32% were found to produce reconstituted soil

mixes with a plasticity index (PI) of 22%, 38% and 53%, respectively (Figure

5.5). These reconstituted clays (SB16, SB24 and SB32) were classified as CI, CH

and CV, respectively (Figure 5.6).

0

10

20

30

40

50

60

10 15 20 25 30 35

Bentonite, %

Pla

stic

ity In

dex

, %

Figure 5.5 Variation of plasticity index with bentonite content.

Chapter 5

102

With the % bentonite values used and the resulting PI values, the activity of each

mix, defined as PI ÷ (% clay < 2 �m), can be calculated (see Table 5.4) and

plotted on the Williams and Donaldson chart (1980) (Figure 5.7) to predict the

expansion potential of the mixes. It is seen that with 16, 24 and 32% bentonite

content the mixes can be separated into three distinct expansion potentials. Hence,

these reconstituted expansive soils were used as test soils for the subsequent tests

like swelling, shrinkage, shear behaviour, hydraulic conductivity, desiccation etc.,

which are described in ensuing chapters.

Table 5.4 Bentonite content and mix properties.

Mix % passing 2 �m (by mass of

dry sand)

Liquid Limit,

%

Plastic Limit,

%

Plasticity Index,

%

Activity,

)%( clayPI

SB16 12.8 43 21 22 1.72

SB24 19.2 60 22 38 1.98

SB32 25.6 77 24 53 2.07

Figure 5.6 Plasticity chart for the sand-bentonite mixtures (BS 5930, 1999).

halla


Chapter 5

103

SB32

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70Clay content (% <0.002mm)

Pla

stic

ity In

dex,

%

Figure 5.7 Expansion potential of sand-bentonite mixes as predicted by the chart of

Williams and Donaldson (1980).

5.5 Hygroscopic moisture content

Bentonite powder, because of its water adsorbent nature, always contains some

hygroscopic moisture content. When the bentonite was added to oven dried sand,

this moisture content contributed to the overall moisture content. In preparing

reconstituted soils of known moisture content the hygroscopic moisture content of

bentonite fractions (Table 5.5) was accounted for. The hygroscopic moisture

content was determined according to AS 1289.2.1.1, 1992.

Table 5.5 Variation of hygroscopic moisture content.

Bentonite fraction,

%

Hygroscopic moisture content,

% 0 0

16 1.35

24 1.82

32 2.50

100 11.0

halla


Chapter 5

104

5.6 Compaction behaviour

As mentioned in Chapter 2 and 3, it was decided to study the influence of recycled

EPS beads on the swell-shrink of expansive soils at soils optimum moisture

content. For that purpose, compaction characteristics of the reconstituted soils

were studied. The influence of EPS on compaction characteristics of soils will be

described in Chapter 6. The typical compaction curves of sand-bentonite (SB)

mixes are shown in Figures 5.8, 5.9 and 5.10 for SB16, SB24 and SB32,

respectively.

SB16

Zero air voids line

Compaction curve

14

15

16

17

18

0 5 10 15 20 25 30 35Moulding moisture content, %

Dry

uni

t wei

ght,

kN/m

3

Figure 5.8 Compaction curve for SB16.

As expected, in each compaction curve, the dry unit weight of the composite

increases with increasing moulding moisture content and after attaining optimum

moisture content, the dry unit weight decreases with further increase in moisture

content. The resulting Optimum Moisture Content (OMC) and Maximum Dry

Density (MDD) are presented in Table 5.6.

Chapter 5

105

SB24

Zero air voids line

Compaction curve

14

15

16

17

18

0 5 10 15 20 25 30 35Moulding moisture content, %

Dry

uni

t wei

ght,

kN/m

3


SB32

Zero air voids line

Compaction curve

14

15

16

17

18

0 5 10 15 20 25 30 35

Moulding moisture content, %

Dry

uni

t wei

ght,

kN/m

3


It has been frequently reported elsewhere that noticeable change in compaction

characteristics of sands can result with the inclusion of bentonite. Ambrosanio

(1955, as cited in deMagistris, 1998) and Kenny et al. (1992) reported that for

Chapter 5

106

uniform fine sands, as used in the present study, there is an increase in dry unit

weight with an increase in bentonite content up to a certain optimum percentage

and then dry unit weight starts to decrease. deMagistris (1998) attributed the

increase in dry unit weight to the reduction of voids in uniform sand by bentonite

addition up to a certain extent. The result from the current study is also in

agreement with the above observation and shown in Figure 5.11.

Table 5.6 Maximum dry unit weight and optimum moisture content of SB mixes.

Bentonite content (%)

Specific gravity

Maximum dry unit weight (kN/m3)

Optimum moisture content (%)

16 2.67 17.07 13.5 24 2.68 17.26 12.0 32 2.69 16.97 14.0

15

16

17

18

0 5 10 15 20 25 30 35

Bentonite, %

Max

imum

dry

uni

t wei

ght,

kN/m

3

Figure 5.11 Variation of maximum dry unit weight with bentonite content.

It is worth noting that Chalermyanont and Arrykul (2005) observed that by

increasing the bentonite content from 0% to 9% in a well graded sand with silt,

the maximum dry unit weight decreases from 19.47 kN/m3 to 18.56 kN/m3 and

the corresponding optimum moisture content increases from 9% to 12%. Similar

observations were made by deMagistris (1998) for a silty sand containing 63%

sand, 21% silt and 16% clay. He noticed that with an increase in bentonite from

10 to 15%, dry unit weight decreased from 15.9 kN/m3 to 15.6 kN/m3 and

Chapter 5

107

optimum moisture content increased from 20% to 22%,. This demonstrates that

the variations in dry unit weights and the corresponding optimum moisture

contents of soil-bentonite mixes depend on the particle size distribution and

coefficient of uniformity of the soils.

5.7 Optimum lime content

From the preliminary studies with dredged soils (Chapter 4) it was observed that

the soil strength can be improved by the addition of stabilisers. For expansive

soils, often lime is chosen for its effectiveness. In this case, since the amount of

stabiliser varies from soil to soil depending on the clay fraction, it is a common

practice to perform the optimum lime content test (Bell, 1996). The most

commonly used procedure is the Eades and Grim procedure (1966). Hence, the

same was performed in the current study to find the suitability of lime for

enhancing the performance of the reconstituted soils. For that purpose, 20 grams

of soil was mixed with 100 ml of distilled water and different amount of hydrated

lime were added. For each amount of lime, the solution was shaken for at least 60

minutes and the pH was measured thereafter. According to the Eades and Grim

procedure (1966), the lowest amount of lime which resulted in a pH of 12.4 was

defined as the optimum lime content.

For the three reconstituted soils SB16, SB24 and SB32, different percentages of

hydrated lime ranging from 2% to 7% by dry weight of SB mix were added to

find the optimum lime content. A typical set of test samples is shown in Figure

5.12 and the designated quantities are shown in Tables 5.7, 5.8 and 5.9 for SB16,

SB24 and SB32 respectively. The variation of pH with % lime is shown in Figure

5.13, from which, by interpolation, the optimum lime content was obtained. As

expected, the variation of optimum lime content with bentonite content was

observed to be increasing as shown in Figure 5.14, due to increase in

exchangeable cations from increased bentonite content.

Chapter 5

108

Figure 5.12 Test method samples.

Table 5.7 Optimum lime content for SB16 mix. Sample

No 1 2 3 4 5 6 7

Sediment weight, g

20 20 20 20 20 20 20

Distilled water, ml

100 100 100 100 100 100 100

Lime weight, g

0 0.4 0.6 0.8 1.0 1.2 1.4

Lime, % 0 2 3 4 5 6 7 pH 10.17 11.99 12.28 12.45 12.54 12.60 12.72

Table 5.8 Optimum lime content for SB24 mix.

Sample No

8 9 10 11 12 13 14

Sediment weight, g

20 20 20 20 20 20 20

Distilled water, ml

100 100 100 100 100 100 100

Lime weight, g

0 0.4 0.6 0.8 1.0 1.2 1.4

Lime, % 0 2 3 4 5 6 7 pH 10.23 11.72 12.18 12.30 12.44 12.55 12.65

Table 5.9 Optimum lime content for SB32 mix.

Sample No

15 16 17 18 19 20 21

Sediment weight, g

20 20 20 20 20 20 20

Distilled water, ml

100 100 100 100 100 100 100

Lime weight, g

0 0.4 0.6 0.8 1.0 1.2 1.4

Lime, % 0 2 3 4 5 6 7 pH 10.44 11.60 12.02 12.26 12.33 12.40 12.53

Chapter 5

109

10

10.6

11.2

11.8

12.4

13

0 1 2 3 4 5 6 7 8Lime, %

pH

SB16SB24SB32

Figure 5.13 Variation of pH for different percentages of lime at different bentonite contents.

0

1

2

3

4

5

6

7

10 15 20 25 30 35Bentonite content, %

Opt

imum

lim

e co

nten

t, %

Figure 5.14 Variation of optimum lime content for different plasticity indices.

Chapter 5

110

The use of lime as a chemical additive in combination with recycled EPS for

improving the swelling and strength characteristics of one of the reconstituted

soils i.e. SB24 will be described in Chapters 7 and 8 respectively.

5.8 Preparation of Soil with EPS (SWEPS) mixes

While the manufacturing of SB mixes as described in foregoing sections was

intended to produce reconstituted soils of varying plasticity, the main test

materials were a composite made by combining the artificial Soils with EPS

(SWEPS). For that purpose, recycled EPS beads (see Chapter 4) were weighed

according to the prescribed content i.e. 0.3, 0.6 and 0.9% by dry mass of the

reconstituted SB soils. Since the SB mix was initially in dry conditions, it was

attempted to introduce EPS beads by dry mixing and to add water thereafter.

However, it was observed that in dry conditions, the SB mix could not mix

homogenously with the EPS beads. As a result, segregation and improper bond

were observed because of the difference in unit weights between the soil mixture

and the EPS beads, and the lack of adhesion between components.

Subsequently, as was done with the dredged soil described in Chapter 4, water

was added to each of the SB samples up to the appropriate optimum moisture

content. The moist SB samples were subsequently sealed in plastic containers and

kept in a humid chamber for a minimum of 14 days. Thereafter, EPS beads were

added in small increments to the moist soil until all the beads were uniformly

distributed within the soil. The mixing of moist soil and EPS beads was performed

in a laboratory using Venco super twin modular system pug mill as shown in the

Figure 5.16. As EPS beads were small in size, no crushing was observed while

mixing in a pug mill. Using this technique, EPS beads could adhere well to the

moist soil. Furthermore, due to the nature of mixing, no EPS beads clusters were

observed during mixing or during compaction (Figure 5.17).

The way the EPS beads are mixed with the soil is similar to that of Maher and

Gray (1990) who reported the performance of fibre reinforced soils. It was

suggested by these authors that the random distribution of fibre offers strength

isotropy and limits potential planes of weakness that can develop parallel to

reinforcement. While the inclusion of EPS beads in the present study was not

Chapter 5

111

intended to reinforce the soil, the random distribution of EPS beads was expected

to avoid the formation of planes of weakness.

Figure 5.15 Venco pug mill used in preparing Figure 5.16 Typical Soil – EPS mix.

SWEPS mixes.

It should be noted that during compaction, EPS beads appeared prone to

segregation and floating at lower moisture contents. This difficulty was more

pronounced with increasing EPS content. Therefore, much care was required to

obtain reasonably uniform distribution of the EPS beads at low moisture contents

(� 8%).

5.9 Specific gravity of SWEPS mixes

The specific gravity of SB mixes was measured individually according to AS

1289.3.5.2- 2002. The average values are shown in Table 5.6. Because of the

lightweight and floating nature of the EPS beads, it is difficult to conduct the

specific gravity of SWEPS mixes by using conventional standard test. Hence by

using Equation 5.1, the specific gravity of SWEPS mix was calculated.

EPSsoil

Mix

GEPS

GSoil

G%%

100

+= (5.1)

Where G Mix = Specific gravity of the SWEPS mix

% Soil = Percentage of soil (by weight) in the composite

% EPS = Percentage of EPS (by weight) in the composite

G Soil = Specific gravity of the soil

G EPS = Specific gravity of the EPS beads

Chapter 5

112

Table 5.10 Specific gravity of the soil with and without EPS beads.

EPS, % Specific gravity of soil at different EPS contents

SB16 SB24 SB32

0.0 2.67 2.68 2.69

0.3 1.91 1.92 1.92

0.6 1.48 1.49 1.49

0.9 1.22 1.22 1.22

It can be seen from the table, because the specific gravity of EPS beads was only

0.02, as expected the specific gravity of the composite is reduced considerably

due to the inclusion of EPS beads to the soil.

5.10 Summary

Sand-Bentonite (SB) mixtures were established by adding uniform sand, passing

450 �m and retained on 75 �m sieve, and bentonite powder. Bentonite contents of

16%, 24% and 32% were selected to prepare reconstituted clays for the

subsequent experimental work of the current research. With the bentonite

contents, clays of intermediate, high and very high plasticity (PI = 22%, 38% and

53%, respectively) were reconstituted.

The Atterberg limit tests showed that with an increase in bentonite content liquid

limit varied non-linearly whereas plastic limit showed a slight or almost negligible

increase. The compaction characteristics showed that the maximum dry unit

weight increased with bentonite content for a uniform sand up to certain

percentage (in the present case up to 24%) and starts to decrease thereafter owing

to the filling of the voids. The optimum lime content increased with the bentonite

content in a linear fashion. The inclusion of EPS beads influenced the specific

gravity of the resulting mix considerably, mainly due to low specific gravity of

EPS beads.

As the EPS beads reduce the specific gravity of the SWEPS mix, it can also have

a marked influence on the dry unit weight of the SWEPS mixes. This was

investigated and described in the ensuing chapter.

113

CHAPTER 6 - COMPACTION OF SOIL WITH EPS (SWEPS) MIXES ___________________________________________________________

The preparation of sand-bentonite (SB) mixes and the rationale behind their

development has been described in Chapter 5. By considering them as the control

soils for the addition of recycled EPS beads, the ensuing chapters discuss various

properties of Soil with EPS (SWEPS) mixes. Since the prime objective of the

current research was to use recycled EPS beads as a swell-shrink modifier in

expansive soils, a compaction study was undertaken on the control soils, with and

without EPS beads, to understand their overall compaction behaviour. The

resulting compaction characteristics are described in this chapter.

6.1 Compaction studies

Many geotechnical structures such as road pavements, railway embankments,

canals, retaining structures, land reclamation etc., require the use of soils as fill

materials. Whenever soil is placed as an engineering fill, it is nearly always

necessary to bring it to a possible densest state to obtain satisfactory engineering

properties which would not be achieved with loosely placed material (Head,

1980). This is achieved by means of compaction of the soil. In the laboratory,

compaction is conducted over a wide range of moisture contents to establish the

maximum mass of dry soil per unit volume achievable for a specified compactive

effort and its corresponding moisture content (AS 1289.5.1.1, 2003).

Similarly, when chemical stabilisers or some other mechanical additives like

fibres or tyre chips are added to the soils to improve or alter their engineering

properties, the composite so formed has to be compacted at its optimum moisture

content to achieve the desired maximum dry unit weight. In soil compaction, soil

particles are allowed to pack more closely together through reduction in the air

voids, with little or no reduction in moisture content, generally by using

mechanical means (Head, 1980).

Effective compaction is an essential pre-requisite for achieving the best

performance from the fill materials used. Compaction improves the engineering

properties of soils such as their strength, compressibility and hydraulic

Chapter 6

114

characteristics (Sridharan and Nagaraj, 2005). In using a composite material, it is

necessary to analyse the compaction characteristics to optimise the proportion of

the materials for compaction so that satisfactory engineering properties can be

arrived at. For example, most of the other engineering properties of soils, such as

the swell-shrink potential, compressive strength, CBR value, permeability,

compressibility and stiffness, are dependent on the moisture and water at which

the soil is compacted. It is known that better compaction leads to greater load

spreading ability and improved resistance to deformation and failure (Lister and

Powell, 1975).

This chapter details the studies conducted to understand the compaction

characteristics of the SWEPS mixes. Even though expanded polystyrene, being

light in weight, reduces the unit weight of the mixes considerably, the aim of these

studies were

(i) To achieve the maximum dry unit weight possible by compaction;

(ii) To observe the effects of EPS content on the maximum dry unit weight

and Optimum Moisture Content (OMC) of the composite;

(iii) To study the variation of dry unit weight with EPS bead content across

different plasticity indices.

For this purpose, three Sand-Bentonite (SB) mixes i.e. SB16, SB24 and SB32

were investigated for three EPS contents, viz., 0.3%, 0.6% and 0.9%.

6.2 Experimental programme

6.2.1 Compaction standards

In the current research, the standard (Proctor) compaction test, AS 1289.5.1.1

(2003), was followed to determine the relationship between the moulding

moisture content and the dry unit weights of the control soils with and without the

addition of EPS. A series of tests were first performed on compacted SB mix

specimens without EPS beads as described in Chapter 5. This was followed by

additional tests, in which EPS beads were added to soil in different percentages.

All the tests were performed using manual compaction. As per AS 1289.5.1.1

(2003), the standard proctor test consists of a mould of nominal volume 1000 cm3,

with an internal diameter of 105 mm and a height of 115.5 mm, in which the soil

Chapter 6

115

is compacted in three equal layers, each was given 25 uniformly distributed blows

by a steel rammer weighing 2.7 kg falling through 300 mm height. The

compaction energy input for the standard compactive effort works out to be 596

kJ/m3. During compaction, the surface of each compacted layer was scarified

before the next one was added to facilitate bonding between the layers. In

addition, before compaction, the inside of the mould was smeared with silicone

grease for easy extrusion.

6.2.2 Specimen preparation

Before compaction, an SB mix was placed in a large steel bowl with sufficient

quantity of distilled water to bring the moisture content of the control soils to the

approximate value (9 to 20%), and was mixed carefully by hand. After mixing,

the moist soil was placed in a zipper storage bag to allow moisture in the soil to

equilibrate for a period of at least 14 days in a humid chamber. One storage bag

was used for each specimen. Recycled EPS beads were then added as described in

Section 5.8 to this mellowed soil. The resulting Soil with EPS (SWEPS) mix was

then compacted in a Proctor mould. For each mix a minimum of five specimens

were compacted with varying initial water content to obtain the compaction curve.

A physical examination of SWEPS mix revealed no significant segregation or

clustering of the beads for most of the EPS dosages during compaction and

extrusion and the mixing produced a uniform specimen as shown in Figure 6.1. At

higher dosages of EPS (�1.0%), segregation was observed. Even for 0.9% EPS

content, a slight segregation of beads was observed on the dry side of optimum.

Moreover, it was observed that these higher fractions (� 1%) of EPS beads would

rebound after compaction and render a loose contact between each layer. This

indicated that no proper bonding occurred between two compacted layers even

though the top surface of the underlying layer was scarified. Hence, EPS content

was limited to 0.9%. To maintain mix consistency at all moisture contents, care

was taken to minimise the effect of segregation while placing and compacting the

SWEPS mix.

Chapter 6

116

Figure 6.1 Extruded SWEPS mix specimen.

The fact that it is possible to compact homogenous laboratory specimens with the

use of standard soil compactive effort suggests that no special compaction

equipment will be needed for compacting SWEPS mixes in-situ.

6.3 Compaction curves

Compaction curves are used to establish the relationships between moulding

moisture content and dry unit weight for all mixes (both SB and SWEPS mixes).

In the present case, since EPS mixing works as a soil replacement, the moulding

moisture content is calculated as the mass of water divided by the total mass of

solids (soil and EPS).

As discussed in Chapter 4, even though there was a reduction in volume upon

oven heating, there was no change in the mass of the EPS beads. Hence, for the

moisture content determination, the oven temperature was set at 105 ± 5° C

without affecting the accuracy of the results.

Chapter 6

117

The compaction curves for the three reconstituted soils, SB16, SB24 and SB32,

mixed with different percentages of EPS beads are shown in Figures 6.2, 6.3 and

6.4, respectively. From these figures it can be seen that for all SWEPS mixes, with

an increase in EPS bead content, the compaction curves shift downwards relative

to those of the control soils (0.0% EPS). Furthermore, they also remain relatively

parallel to their respective control compaction curve, indicating the effect of soil

replacement on weight reduction.

SB16

0.6% EPS

0.0% EPS

0.3% EPS

0.9% EPS

10

12

14

16

18

5 10 15 20 25Moulding moisture content, %

Dry

un

it w

eigh

t, kN

/m3

Figure 6.2 Compaction curves for SB16 at different EPS contents.

The addition of EPS beads did not produce any significant variation in the shape

of compaction curves. The similarity in compaction curves at all EPS contents

indicates that the SWEPS mixes exhibit the same type of compaction behaviour as

the corresponding control soils, but with decreasing dry unit weights.

Chapter 6

118

SB24

0.3% EPS

0.6% EPS

0.9% EPS

0.0% EPS

10

12

14

16

18

5 10 15 20 25 30


Dry

uni

t wei

ght,

kN/m

3


SB32

0.3% EPS

0.6% EPS

0.9% EPS

0.0% EPS

10

12

14

16

18

5 10 15 20 25


Dry

uni

t wei

ght,

kN/m

3


For cohesive soils, a compaction curve with a well defined peak can usually be

obtained. However, as the % of fines and the plasticity increase, the compaction

Chapter 6

119

curve becomes flatter and therefore less sensitive to moisture content. This is

certainly the case for the present study for the soils without EPS content, as the

bentonite content varies from 16 to 32%. Furthermore, from the Figures 6.2 to 6.4

it can be observed that for a considerable variation in moulding moisture content,

only a marginal change in dry unit weight is obtained for different EPS contents

similar to that of the control soil. From compaction point of view, this also

suggests that the lightweight SWEPS mix can be conveniently handled with

conventional equipment, and compacted over a broader range of moisture

contents (say 10 – 20%), to achieve the desired field density, if it is utilised as an

embankment fill. This type of behaviour was also observed by Indraratna (1992)

while studying the characteristics of fly ash for its utilisation as an embankment

fill material. However, when considered from swelling point of view, compacting

on wet side of optimum would give better mixing of soil and EPS and reduced

swelling.

6.4 Effects of EPS on the maximum dry unit weight

The variation of maximum dry unit weight with the addition of EPS beads to the

soils at different bentonite contents is presented in Figure 6.5. As expected, the

maximum dry unit weight decreases with an increase in EPS content owing to

EPS beads lightweight. For the control soil, the maximum dry unit weight

increases with bentonite content of up to 25% and decrease thereafter, while for

SWEPS the maximum dry unit weight decreases with bentonite addition.

For all soil types, the decrease in the maximum dry unit weight due to EPS

inclusion is of the same trend (Figure 6.6). The maximum dry unit weight of SB16

soil goes down from 17.06 kN/m3 to 13.24 kN/m3 (22.4%) with a change from

0.0% to 0.9% EPS content. Similarly, the decrease is from 17.27 kN/m3 to 12.56

kN/m3 (27.3%) for SB24; and from 16.97 kN/m3 to 12.26 kN/m3 (27.8%) for

SB32 for the same range of EPS contents.

Chapter 6

120

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

12

13

14

15

16

17

18

15 17 19 21 23 25 27 29 31 33Bentonite content, %

Max

imum

dry

uni

t wei

ght,

kN/m

3

Figure 6.5 Variation of maximum dry unit weight of soil with different percentages

of EPS at different bentonite contents.

SB16

SB24

SB32

12

13

14

15

16

17

18

0 0.2 0.4 0.6 0.8 1EPS, %

Max

imum

dry

uni

t wei

ght,

kN/m

3

Figure 6.6 Variation in maximum dry unit weight with EPS content for different soils.

Chapter 6

121

6.4.1 Factors influencing the reduction in dry unit weight

The characteristics of EPS beads could have contributed to the reduction in dry

unit weight viz., low bulk density and compression resistance. In addition, EPS

beads may have caused some obstruction to the reorientation of soil particles.

• Low bulk density of EPS beads

The reduction of dry unit weight with the addition of EPS beads can be mostly

attributed to the EPS’s very low bulk density. A few percent increase in weight of

EPS beads can result in a significant reduction in the combined particle density as

shown in Table 5.10, because of the volume of soil replaced by the EPS beads.

• Resistance to compression

Compactibility of the mix could be reduced at higher EPS contents, as was

observed in Chapter 4 (dredged soil and EPS beads). This is because of the

resistance offered by EPS beads to further densification, possibly through energy

absorption and elastic rebound. Similar behaviour was observed by Hoare (1979)

while performing compaction on granular soils with randomly oriented discrete

fibres. This study reported that more compactive effort was needed to increase the

fibre content. Similarly, Tatlisoz et al. (1997) observed that addition of tyre chips

to clayey soils caused reduction in dry unit weight due to the absorption of

compaction energy by the tyre chips.

• Resistance to reorientation

To some extent, the EPS beads may have obstructed the reorientation of soil

particles into denser configuration during compaction by the formation of “EPS

clods” at higher EPS content.

6.5 Effect of EPS on optimum moisture content

As described in the previous section, the addition of EPS beads to expansive soil

reduces the maximum dry unit weight for the same compactive effort; however, it

has less impact on the optimum moisture content of the soil. The relatively flat

compaction curves create some difficulty in determining the optimum moisture

contents; however, a close observation suggests that these can be assumed to

coincide with those of the control soils.

Chapter 6

122

6.6 Effect of degree of compaction

It is well known that when modified compactive effort is applied to a soil, higher

maximum dry unit weight and lower OMC values can be achieved when

compared with those of standard compactive effort. While modified compaction

was not utilised in the present case, it could be expected that the higher

compactive effort would produce an increase in the maximum dry unit weight of

the SWEPS mix. At the same time, lower OMC would result in a lower maximum

EPS content that could be added into the mix (to avoid segregation problem).

The higher compactive effort may therefore reduce the benefit of using the EPS as

a lightweight fill material. Hence, before selecting the degree of compaction, the

relevant strength, swell-shrink and settlement criteria should be studied. An

appropriate mix design procedure should subsequently be adopted to optimise the

EPS content in order to satisfy the above criteria (which may or may not lead to

the addition of chemical stabilisers).

6.7 Comparison of compaction characteristics of SWEPS mixes with

other composite soils

Previous studies showed that soil composites such as fibre added soils, tyre chips

added soils, and EPS added soils exhibit the typical compaction behaviour of

soils. However, with regards to the effect of added reinforcements on MDD and

OMC of cohesive soils (Table 6.1) it is clear that there have been wide-ranging

results reported in the literature. With additional fibres, some authors found MDD

increased but others found the opposite. Similarly, on OMC, there were similar

conflicting results. However, overall, the observed trend is that with additional

fibres, MDD was lowered but OMC was not affected significantly.

Of particular interest, Yasufuku et al. (2002) studied the compaction behaviour of

Heat Compressed and Crushed EPS (HCCE) mixtures for possible use as a

lightweight fill material by mixing with decomposed granite with a specific

gravity (Gs) of 2.62. The HCCE was obtained first by melting the waste EPS at

230°C hot blast and solidified before being granulated by a crusher. Once mixed

with the soil, these crushed EPS ingots (Gs = 1.0) produced a composite with

similar behaviour as what was obtained in the present investigation (Figure 6.7).

Chapter 6

123

Table 6.1 Effect of fibre reinforcement on MDD and OMC of cohesive soils.

Soil type Fibre type Effect on MDD Effect on OMC

Silty sands1 Discrete polypropylene fibres

Decreased Decreased

Black cotton soil, India2

Discrete polypropylene fibres

Decreased Decreased

Residual silt3 Polypropylene fibres Modest increase Decreased

Kaolinite4 Fibre No much variation

No much variation

Clay5 Fibres No much variation

No much variation

Pond ash6 Fibres No much variation

No much variation

Silty sand6 Fibres No much variation

No much variation

Fly ash (Rajghat, India)7

Fibres Increased Decreased

Fly ash (Dadri, India)7

Fibres No much variation

No much variation

Clayey soil (PI = 47%)8

Discrete polypropylene strands (1 inch long)

Increased Decreased

Flyash9 Rubber and bentonite Decreased No much variation

Black cotton soil, India (CH)10

Geotextile woven fabric (0.5 mm diameter) Fibre glass pieces (0.1 mm diameter)

Increase Decrease

Clay11 Polypropylene fibres No much variation

No much variation

Decomposed granite12

Heat compressed and crushed EPS (HCCE)

Decreases No variation

1Setty and Rao (1987); 2Setty and Murthy (1990); 3Fletcher and Humphries (1991); 4Maher and Ho (1994); 5Al-Wahab and El-Kedrah (1995); 6Kumar et al. (1999); 7Kaniraj and Gayathri, (2003); 8Zhang et al. (2003); 9Cocka and Yilmaz (2004); 10Gosavi et al. (2004); 11Miller and Rifai (2004); 12Yasufuku et al. (2002).

Chapter 6

124

Figure 6.7 Compaction curves of decomposed granite mixed with HCCE

(after Yasufuku et al., 2002).

In the present investigation, the decrease in dry unit weight with the addition of

recycled EPS beads is in agreement with other lightweight recycled materials or

fibres. However, in terms of OMC, the results of the current study show that

OMC is not sensitive to the change of material composition. This is because EPS

is very light in weight than the other recycled materials.

6.8 Volumetric proportions

It was expected that with the addition of recycled EPS beads there would be

reduction in the volume of soil in the composite. To understand the volumetric

proportions of soil and EPS within the composite material, tests were conducted

on the dry EPS beads to find the dry unit weights of EPS in loose and compacted

(with standard energy) conditions.

It was observed that in a loose state the dry unit weight of recycled EPS beads

alone was 0.16 kN/m3, whereas after compaction in a standard compaction mould,

the dry unit weight increased to 0.19 kN/m3. This increase in unit weight could be

attributed to the compression of EPS beads and reduction in voids during

compaction. These values indicated that the method of placing and compacting

influenced the dry unit weight of the EPS beads. These values further indicated

that the standard compaction produced a decrease in the volume of EPS beads of

13.5%.

Chapter 6

125

The calculation of volumetric proportions were based on the assumption that the

mass of each component of the composite would have reached their respective

unit weight had they been individually compacted using standard compaction as

illustrated in the Figure 6.8. That means that the maximum dry unit weight of the

soil is at its corresponding optimum moisture content and the dry unit weight of

EPS beads could at its compacted state.

The reduction in dry unit weight of the composite with the addition of recycled

EPS beads was therefore calculated based on the following considerations.

• The maximum dry unit weight of compacted EPS was achieved.

• The maximum dry unit weight of soil at its optimum moisture content under

standard compaction was considered. It varied with the bentonite content

added to the soil (Table 5.5).

• Compactive effort was the same for both soil and SWEPS mix. Standard

compactive effort was followed as per standard.

• The volume of soil was calculated based on its mass in the SWEPS mix. Then

EPS volume was the difference between composite volume and soil volume.

(a) Composite (b) Individual material

Figure 6.8 Soil – EPS volumes (a) as a composite (b) as individual components.

Volume of EPS in all the soils is based on the following equations

SoilCompEPS VVV −= (6.1)

Chapter 6

126

Where VEPS is volume of EPS, %

Vcomp is volume of SWEPS mix, % (this is expressed as 100%)

Vsoil is volume of available soil, %, it is calculated based on Equation 6.2

Soil

SoilSoil

WV

ρ= (6.2)

Where Wsoil is the dry mass of soil in the composite, kg

soilρ is the maximum dry density of soil at its optimum moisture content,

kg/m3

Figure 6.9 shows the volume occupied by the EPS in SWEPS mix at 0.3, 0.6 and

0.9% of EPS for soils with bentonite contents of 16% (SB16), 24% (SB24) and

32% (SB32).

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1EPS, %

Vol

ume

of E

PS

in S

WE

PS

mix

es, %

SB16SB24SB32

Figure 6.9 Generalised volumes of EPS in SWEPS mix at different % of EPS by

dry weight of soil.

The fitting line is linear and passes the origin. The regression coefficient (r2) is

0.998. At 0.3 % by dry weight of soil the EPS occupies 7.5% of the volume and at

Chapter 6

127

0.6% it occupies nearly 15.5% and finally at 0.9% by dry weight it occupies

22.25% of the total volume.

This addition of EPS will decrease the unit weight of the SWEPS mix as

discussed earlier. However, the strength of the mix has to be carefully considered

in the design of mix proportions for the SWEPS mix. If required, stabilisers may

be used to compensate the loss of strength due to the addition of EPS.

6.9 Predictive model for dry unit weight

The dry unit weight behaviour of SWEPS mixes was examined by focussing on

the influence of the soil type (PI of 22, 38 and 53%) and EPS content (0.0, 0.3, 0.6

and 0.9%).

The experimental data was quantitatively analysed by multiple regression models

by correlating dry unit weight with PI and EPS. The equation obtained from the

multiple regression analysis is

EPSPId 91.4013.068.17 −−=γ (6.3)

Where dγ is dry unit weight, kN/m3,

PI is plasticity index, %

EPS is quantity of EPS, %

This equation is valid only for the range of soils tested and for EPS contents

evaluated. The validity of this equation was checked and a comparison was made

between the measured and predicted values for the dry unit weight as shown in

Figure 6.10. Figure 6.11 shows the experimentally obtained dry unit weight vs.

the predicted values. The regression analysis of this prediction models gives R2

value of 0.9858.

Chapter 6

128

12

13

14

15

16

17

18

19

15 20 25 30 35 40 45 50 55

Plasticity index, %

Dry

uni

t wei

ght,

kN/m

30.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model

Figure 6.10 The relation between the PI and the measured and predicted values of

dry unit weight.

R 2 = 0.9858

10

15

20

10 15 20Actual dry unit weight, kN/m3

Pre

dict

ed d

ry u

nit w

eigh

t, kN

/m3

Figure 6.11 The relation between measured and predicted dry unit weights.

6.10 Summary

The overall compaction behaviour of SWEPS mixes is presented in this chapter.

Three EPS contents of 0.3%, 0.6% and 0.9% were added to the test soils and

compacted according to standard Proctor compaction method. It was observed

that the addition of EPS reduced the dry unit weight. This reduction in dry unit

weight can be attributed to the specific gravity of the recycled EPS beads. In

Chapter 6

129

addition, the resistance offered by EPS (elastic rebound) can reduce the

compactability of the mix at higher EPS contents.

It was also observed that the shapes of SWEPS compaction curves were similar to

that of the control soils but with reduced maximum dry unit weight values. On

volumetric proportions it has been shown that for the given soil at the maximum

possible mixing rate of 0.9% by dry weight, recycled EPS occupy 22.25% of the

total volume of the mix.

Increasing the compaction energy can increase the dry unit weight of the SWEPS

mixes owing to the compression of EPS beads and also due to the limitation in the

inclusion of the EPS beads due to reduced moisture content at higher compactive

energies.

It has been demonstrated that the inclusion of EPS into a soil can significantly

reduce the dry unit weight of the composite thus formed. In the field, EPS mixing

and compaction can be performed at optimum moisture content of the soil. The

lightweight characteristics of the SWEPS suggest that the material may be

suitable for use as a lightweight backfill. The use of SWEPS behind a retaining

wall is expected to reduce the lateral thrust on the wall, which will in turn result in

a more economical wall design.

Following these compaction studies, keeping in view with the main focus of this

research, a series of swelling and shrinkage tests were performed on the SB and

SWEPS mixes at their respective MDD and OMC conditions. The following

chapter discuss the outcome of those experiments.

Chapter 6

130

131

CHAPTER 7 – SWELLING AND SHRINKAGE STUDIES ON SWEPS MIXES

As discussed in Chapter 3, the prominent feature of expansive soils is their swell-

shrink potential due to moisture changes. This feature is considered as an

important factor in geotechnical design because it often causes unpredictable

ground movements. The swell of soil is due to formation of a moisture film

around the soil particles as a result of reaction between the clay particles and

water (Low, 1992). Even though swelling can occur due to load reduction, the

problem of swelling is more severe with water imbibition (Sivapulliaiah et al.,

1996).

As mentioned in Chapters 1 and 2, an attempt was made to mix recycled EPS

beads with reconstituted expansive soils in assessing their potential as a swell-

shrink modifier. Based on the compaction characteristics described in Chapter 6, a

series of free swell tests, swell pressure tests, and shrinkage tests were performed

to investigate the relationships between swell-shrink characteristics and EPS

contents of the SWEPS mixes at their maximum dry unit weights and optimum

moisture contents. The three test soils (SB16, SB24 and SB32) and four EPS

contents (0%, 0.3%, 0.6% and 0.9%) were investigated further in this study.

In this chapter, the specimen preparation techniques and test procedures are

outlined together with the test results and discussion on swelling, cyclic swelling

and reduction in swelling. Furthermore, the effects of recycled EPS beads on the

axial, diametral and volumetric shrinkage of expansive soils are also described.

7.1 Compaction of SWEPS specimens

While EPS block can be cut using either a fine-blade saw or a hot-wire apparatus

(Horvath, 1995), the nature of sand and bentonite mixes in the present research

does not allow sawing following compaction. Furthermore, it is also very difficult

to perform hot-wire trimming. Hence, static compaction method was selected for

preparing specimens for swelling, consolidation, suction, desiccation and

hydraulic conductivity tests.

Chapter 7

132

In static compaction, the soil sample is compacted by a gradually applied

monotonic force. Venakatarama Reddy and Jagadish (1993) have described two

types of static compaction. They are the constant peak stress – variable stroke

compaction method and the variable peak stress – constant stroke compaction

method.

In the constant peak stress – variable stroke compaction method, the applied stress

is gradually increased at a defined rate until a specific peak stress is reached. The

thickness of the compacted specimen depends on the moisture content. While the

resulting compaction curves are similar to those of dynamic compaction

procedure, the energy input varies with the moisture content.

In the variable peak stress – constant stroke compaction method, a static force is

gradually applied until a specific final thickness corresponding to the required

volume is achieved. In this case the energy input is variable but can be derived

indirectly and specified if necessary (Montanez, 2002).

The variable peak stress – constant stroke compaction method was used in the

current research to obtain specimens with constant initial thickness. A layer of

cling film (plastic wrap) was placed over the piston during the compaction process

in order to stop the compacted material from adhering to the top piston.

7.2 Swelling Characteristics of SWEPS mixes

7.2.1 Common test procedures

The most common methods for determining the magnitude of swell in soils

involve the use of conventional one-dimensional consolidation (oedometer)

apparatus. A wide variety of test procedures have been used in the past as

summarised by Nelson and Miller (1992). However, basically there are two test

types available for finding the free swell and swell pressure of the soil. They are

referred to as the “free swell” (also called “vertical swell” or “swell deformation”

or “swell strain”) test; and the “swell pressure” (also called “constant volume”)

test (Sridharan et al., 1986). In this thesis, the terms “free swell” and “swell

pressure” as prescribed in ASTM D 4546-96 are used.

Chapter 7

133

In the free swell test, the specimen is allowed to swell under a seating pressure,

generally 6.9 kPa (1 psi), by submersion in distilled water. After attaining an

equilibrium condition, the specimen is then loaded and unloaded following the

conventional oedometer test procedure. Through this procedure the magnitude of

both free swell and swell pressure can be obtained from the same soil specimen.

In contrast, in the constant volume test, the applied load is gradually increased in

order to keep the specimen’s volume unchanged after being submerged in distilled

water. The final load at which no further deformation occurs is taken as the swell

pressure.

Gilchrist (1963, cited in Nishimura, 2001) stated that the swell pressure obtained

from the free swell test was different from that obtained from the constant volume

test. However, other researchers (Borgesson, 1990; El-Sohby, 1994) obtained

comparable results in magnitude of swell especially at high density.

Notwithstanding this discrepancy, both the free swell and the swell pressure tests

were performed in the current study to reflect the two different test conditions.

7.2.2 Specimen preparation

According to El-Sohby and Rabba (1981), Yevnin and Zaslavsky (1980), initial

moisture content and initial dry unit weight are important factors affecting the

swell behaviour of expansive soils. In the present investigation, the specimens

were produced at their estimated maximum dry unit weight and at their

corresponding optimum moisture content as obtained in Chapter 6. The required

amount of SWEPS mixes were compacted statically in a conventional oedometer

ring using variable peak stress – constant stroke compaction method as described

in Section 7.1, until the desired dry unit weight corresponding to the standard

Proctor compactive effort was achieved.

The stainless steel oedometer ring was 70 mm in diameter and 19 mm in height.

Silicone grease was smeared on the inside of the ring before compaction to reduce

the side friction between the ring and soil mix specimen. To control the dry unit

weight, the specimens were compacted statically using a hydraulic jack as shown

in the Figure 7.1.

Chapter 7

134

Figure 7.1 Diagrammatic representation of static compaction of oedometer

specimen.

The oedometer ring with top clamping ring was positioned and screwed on to a

base plate (fixed ring type). Then the desired amount of SWEPS mix was placed

inside the ring and the assembly was positioned under the hydraulic jack. The

specimen was compacted in three equal layers to maximise the overall uniformity

and each layer was scarified before compacting the next layer for proper bonding.

After compaction, the ring was released and placed in the oedometer cell with air-

dry porous stones on top and bottom of the specimen. To protect the porous stones

from soil contamination, a filter paper was placed between the specimen and the

porous stone on both ends. Subsequently, the entire assembly was positioned in

the loading frame and the deflection reading was adjusted to zero. The specimen

was subsequently inundated with distilled water.

7.2.3 Test procedure

Vertical loading was applied using a Wykeham-Farrance oedometer loading frame

(Bishop type, rear loading, lever arm bench model). The free swell test method

was used to determine the swelling deformation of the specimens (AS 1289.7.1.1-

2003) and constant volume test was chosen for swell pressure studies (ASTM D

4546, 1996).

Chapter 7

135

In the free swell test, the specimen was firstly loaded with a seating pressure of

6.9 kPa (AS 1289.7.1.1-2003 recommends a seating load of 25kPa. However, as

suggested by Sridharan et al., 1986, 6.9 kPa seating pressure was used in the

present study) and then inundated with distilled water. Under this constant

pressure, the axial deformation was measured with a dial gauge of 0.002 mm

precision. Each test was continued for at least 15 days to establish the relationship

between the free swell and the elapsed time from the start of the inundation. The

swell was observed to be increasing even after two weeks as shown in Figures 7.2

to 7.4, hence hyperbolic curves were fitted to the test data as described in ensuing

section.

In the constant volume test (AS 1289.7.1.1 (2003)) not specifies this type of test

hence ASTM D 4546-96, Method C was followed) after placing the specimen in

the oedometer loading frame, water was supplied and the swelling was contained

by periodically increasing the load on the specimen with due care to avoid

compression of specimen. This test was continued until there was no further

volume change in the specimen in between two successive readings.

7.2.4 Results and discussion

7.2.4.1 Free swell

Figures 7.2, 7.3 and 7.4 show the relationships between free swell and elapsed

time for the three soils (SB16, SB24 and SB32), with and without EPS bead

inclusion. Free swell is the ratio of the amount of swell to the original thickness of

the specimen, expressed as percentage. It can be observed from the figures that the

magnitude of free swell is affected by the EPS content in the soil.

It can be observed from the Figures 7.2 to 7.4 that the magnitude of free swell

decreases as the EPS content increases from 0.0% to 0.9%. In absolute terms,

when compared with the free swell of control soil, the increase in EPS content

from 0.3% to 0.9% caused a reduction in free swell ranging 10 to 63% for SB16,

13 to 50% for SB24 and 13 to 48% for SB32 respectively. Furthermore, following

the commencement of the test, the magnitude of free swell was found to be

relatively low especially for higher EPS contents across all soil types.

Chapter 7

136

0

4

8

12

16

20

24

0 5000 10000 15000 20000Time, min

Fre

e sw

ell,

%

SB16, 0.0% EPSSB16, 0.3% EPSSB16, 0.6% EPSSB16, 0.9% EPS

Figure 7.2 Variation of free swell with time at different EPS contents for SB16.

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000Time, min

Fre

e sw

ell,

%

SB24, 0.0% EPSSB24, 0.3% EPSSB24, 0.6% EPSSB24, 0.9% EPS


Chapter 7

137

0

5

10

15

20

25

30

35

40

45

50

0 5000 10000 15000 20000Time, min

Free

sw

ell,

%

SB32, 0.0%EPSSB32, 0.3% EPSSB32, 0.6% EPSSB32, 0.9% EPS


The reduction in magnitude of free swell may be attributed to the slow rate of

water uptake by soil particles due to EPS beads obstruction. Generally, the

interaction of water with clay surfaces reduces the chemical potential of the water,

thereby generating a gradient in the chemical potential that causes additional

water to flow into the system (Du and Hayashi, 2000). However, as EPS beads are

inert, non-water absorbent and impermeable in nature, the water cannot flow

through the EPS beads. The EPS beads would rather act as obstructions for the

movement of water. Furthermore, it can be recalled that EPS beads replace soil

volume as discussed in Chapter 6. Hence, the quantity of soil available for

swelling is considerably less, thus producing reduced free swell. In this case, the

bentonite content in the soil plays a significant role in swelling as discussed later

in this section (see, influence of clay content for a given EPS content).

Hyperbolic curves

The time to reach the maximum free swell depends on the available expansive

clay fraction in the soil. In general, instead of reaching a peak value, the swelling

curve flattens up and becomes asymptotic to a line parallel to the horizontal axis.

The distance between this line and the horizontal axis is the maximum free swell

(esmax).

Chapter 7

138

In the present investigation, from Figures 7.2 to 7.4, it can be observed that free

swell is still progressing at a slow rate even after 14 days of water uptake. This is

not surprising as Komine and Ogata (1999) reported that for bentonite contents

greater than 20% swelling would continue for a long time than the lesser bentonite

contents. In the present investigation, instead of extending the test duration,

hyperbolic models were used to predict the maximum free swell values.

Many attempts have been made in the past to model soil swelling by means of a

rectangular hyperbola. For example, Dakshinamurthy (1978) observed that the

maximum swelling can be predicted by the hyperbolic model over a short interval

of time. Similar modelling techniques were also reported by other researchers

(Rao and Kodandaramaswamy, 1981; Sridharan et al., 1986; Sivapullaiah et al.,

1996; Komine and Ogata, 1999; Sridharan and Gurtug, 2004).

The curves of free swell versus time can be approximated by the hyperbolic

equation as shown in Equation 7.1

btat

es += (7.1)

Where es is the free swell at time, t,

t is the time in minutes from the start of the inundation and

a and b are constants determined by fitting procedures as described below.

To assess whether the observed readings were following a hyperbolic relationship,

a plot was drawn between time vs. time / % free swell as shown in Figure 7.5 for

all EPS contents. If the readings follow a straight line relationship, it is an

indication that hyperbolic relation exists between those two parameters. In all the

cases except for 0.9% EPS content a straight line relationship was obtained.

Similar behaviour was also observed in SB24 and SB32 soils. The intercept with

the y-axis is denoted by ‘a’ and the slope of the line is denoted by ‘b’.

With the calculated values of ‘a’ and ‘b’, using Equation 7.1, hyperbolic swell

curves can be obtained and compared with the experimental curves at different

EPS contents (Figures 7.6 through 7.17). In almost all the cases the curves

Chapter 7

139

obtained from the experimental work have showed a good agreement with the

curves generated from the hyperbolic modelling.

SB16

0.0% EPS

0.3% EPS0.6% EPS

0.9% EPS

(R 2 = 0.996)

(R 2 = 0.9863)(R2 = 0.9951)

(R 2 = 0.956)

0

400

800

1200

1600

2000

2400

2800

3200

0 5000 10000 15000 20000 25000Time, min

Tim

e/ fr

ee s

wel

l, m

in/%

Figure 7.5 Time-Free swell hyperbolic relationship for SB16.

Komine and Ogata (1999) found that hyperbolic curves could approximately fit

their experimental curves after 10000 minutes. However, in the present case the

model could reasonably match the experimental data after 5000 minutes.

The maximum free swell (esmax) is obtained from the asymptotic line of the

hyperbola as:

(%)11

lim)(limmax bb

ta

teetsts =

��

�

�

��

�

�

+��

��

�==

∞→∞→ (7.2)

The predicted maximum free swell from the models are compared with those

recorded at the end of the tests (i.e. 14 days) in Figure 7.18 for soils SB16, SB24

and SB32. As expected, there is a noticeable difference between the two because

of the gradual progression of swelling. These hyperbolic fitted values were used

in the subsequent analysis and interpretation.

Chapter 7

140

SB16, 0.0% EPS

0

4

8

12

16

20

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

SB16, 0.3% EPS

0

4

8

12

16

20

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

Figure 7.6 Free swell vs. time for SB16 at 0.0% EPS content. Figure 7.7 Free swell vs. time for SB16 at 0.3% EPS content.

SB16, 0.6% EPS

0

4

8

12

16

20

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental dataHyperbolic fit

SB16, 0.9% EPS

0

4

8

12

16

20

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %



Chapter 7

141

SB24, 0.0% EPS

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

SB24, 0.3% EPS

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g,. %

Experimental data

Hyperbolic fit

Figure 7.10 Free swell vs. time for SB24 at 0.0% EPS content Figure 7.11 Free swell vs. time for SB24 at 0.3% EPS content

SB24, 0.6% EPS

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

SB24, 0.9% EPS

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000 25000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

Figure 7.12 Free swell vs. time for SB24 at 0.6% EPS content Figure 7.13 Free swell vs. time for SB24 at 0.9% EPS content

Chapter 7

142

SB32, 0.0% EPS

0

10

20

30

40

50

0 5000 10000 15000 20000Time, min

Fre

swel

ling,

%

Experimental data

Hyperbolic fit

SB32, 0.3% EPS,

0

10

20

30

40

50

0 5000 10000 15000 20000Time, min

Free

sw

ellin

g, %



SB32, 0.6% EPS

0

10

20

30

40

50

0 5000 10000 15000 20000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit

SB32, 0.9% EPS

0

10

20

30

40

50

0 5000 10000 15000 20000Time, min

Free

sw

ellin

g, %

Experimental data

Hyperbolic fit


Chapter 7

143

SB16

Hyperbolic fit

Experimental data

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1EPS, %

Max

imum

free

sw

ell,

%

(a)

SB24Hyperbolic Fit

Experimental data

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1EPS, %

Max

imum

free

sw

ell,

%

(b)

SB32

Experimental data

Hyperbolic fit

0

10

20

30

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1EPS, %

Max

imum

free

sw

ell,

%

(c)

Figure 7.18 Differences in maximum free swell values between experimental data and

hyperbolic approximations (a) SB16, (b) SB24 and (c) SB32.

Chapter 7

144

Optimum EPS content

The gradual reduction in free swell with increasing EPS content implies that there is a

possibility that when a sufficient amount of EPS is included, the free swell of the

SWEPS mix will be negligible due to the soil replacement affect which allows all

remaining swelling deformation to be absorbed by the EPS beads through

compression.

By extrapolating polynomially, the relationship between free swell and EPS content

for all soils is shown in Figure 7.19; the intersection with the abscissa corresponds

with the EPS content at which the soil will not swell. Theoretically, this value may be

called the “zero-percent-free swell EPS content”. However, in practice, the relatively

high EPS content may cause problems with the possible material segregation,

compaction difficulty and strength reduction (see Chapter 4).

SB16

SB24

SB32

0

10

20

30

40

50

60

70

80

0 0.25 0.5 0.75 1 1.25 1.5 1.75EPS, %

Max

imum

free

sw

ell,

%

Figure 7.19 Variation of maximum free swell with EPS content.

Influence of clay content for a given EPS content

For any particular EPS content, the influence of clay content on the magnitude of

swell in the composite is noticeable. The variation of maximum free swell with

bentonite content (SB16, SB24 and SB32) is presented in Figure 7.20 and the

Chapter 7

145

variations of free swell for 0%, 0.3%, 0.6% and 0.9% EPS contents with elapsed time

are presented in Figures 7.21, 7.22, 7.23 and 7.24 respectively. From these figures it

can be observed that for any specific EPS content, the higher the clay content (in this

study it is the bentonite content), the higher the free swell is. The magnitude of free

swell is dependent not only on EPS content but also on the available expansive clay

fraction in the soil. Hence, for mixing EPS beads to expansive soils, each soil needs to

be specifically analysed for its potential swell reduction.

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

10

20

30

40

50

60

70

80

12 17 22 27 32

Bentonite content, %

Max

imu

m fr

ee s

wel

l, %

Figure 7.20 Variation of maximum free swell with bentonite content.

Chapter 7

146

0.0% EPS

0

10

20

30

40

50

0 5000 10000 15000 20000 25000Time, min

Fre

e sw

ell,

%

SB16SB24SB32

0.3% EPS

0

10

20

30

40

50

0 5000 10000 15000 20000 25000Time, min

Free

sw

ell,

%

SB16SB24SB32

Figure 7.21 Variation of free swell with clay content for 0.0% EPS. Figure 7.22 Variation of free swell with clay content for 0.3% EPS.

0.6% EPS

0

10

20

30

40

0 5000 10000 15000 20000 25000Time, min

Fre

e sw

ell,

%

SB16SB24SB32

0.9% EPS

0

10

20

30

0 5000 10000 15000 20000 25000Time, min

Free

sw

ell,

%

SB16SB24SB32

Figure 7.23 Variation of free swell with clay content for 0.6% EPS. Figure 7.24 Variation of free swell with clay content for 0.9% EPS.

Chapter 7

147

Predictive model for maximum free swell

The maximum free swell behaviour of SWEPS mixes was examined by focussing

on the influence of the soil type (PI of 22, 38 and 53%) and EPS content (0.0, 0.3,

0.6 and 0.9%).


by correlating maximum free swell with PI and EPS. The equation obtained from

the multiple regression analysis is

EPSPIFS 15.1977.06 −+= (7.3)

Where FS is maximum free swell, %,





between the measured and predicted values for the maximum free swell as shown

in Figure 7.25. Figure 7.26 shows the experimentally obtained maximum free

swell vs. the predicted values. The regression analysis of this prediction models

gives R2 value of 0.9693.

0

5

10

15

20

25

30

35

40

45

50

15 20 25 30 35 40 45 50 55Plasticity Index, %

Max

imu

m fr

ee s

wel

l, %


Figure 7.25 Relation between the PI and the measured and predicted values of

maximum free swell.

Chapter 7

148

R 2 = 0.9693

0

20

40

60

0 20 40 60Actual maximum free swell, %

Pre

dict

ed m

axim

um fr

ee s

wel

l, %

Figure 7.26 The relation between measured and predicted maximum free swell.

7.2.4.2 Swell pressure

In this study, the swell pressure is defined as the pressure to maintain the

specimen’s volume constant while undergoing saturation in between two

successive readings. Variation of maximum swell pressure with EPS for the three

soil types is shown in Figure 7.27. From the figure, the similar trend as was

observed in the free swell tests (Figure 7.19) can be seen i.e. swell pressure

decreases with an increase in EPS content irrespective of the bentonite content.

SB16

SB24

SB32

0

20

40

60

80

100

120

140

0 0.25 0.5 0.75 1 1.25 1.5 1.75

EPS, %

Max

imum

sw

ell p

ress

ure,

kP

a

Figure 7.27 Variation of maximum swell pressure with EPS content.

Chapter 7

149

By linearly extrapolating the relationship between maximum swell pressure and

EPS content for all soils as shown in Figure 7.27, the intersection with the

abscissa corresponds with the EPS content at which the soil will produce zero

swell pressure. Comparison of the “zero-percent-swell pressure EPS content”

values in this figure with those from Figure 7.19 (zero-percent-free swell EPS

content) show a good agreement, the EPS content vary in the range of 1.3 to 1.6%

for both the cases. Variation of the maximum swell pressure with bentonite

content is shown in Figure 7.28. From this figure it can be observed that swell

pressure, like free swell, also varies with the bentonite content in addition to EPS

content.

0.6% EPS

0.0% EPS

0.3% EPS

0.9% EPS

0

20

40

60

80

100

120

140

15 17 19 21 23 25 27 29 31 33


Max

imu

m s

wel

l pre

ssur

e, k

Pa

Figure 7.28 Variation of maximum swell pressure with bentonite content.

Predictive model for maximum swell pressure

The maximum swell pressure of SWEPS mixes was examined by focussing on the

influence of the soil type (PI of 22, 38 and 53%) and EPS content (0.0, 0.3, 0.6

and 0.9%).


by correlating maximum swell pressure with PI and EPS. The equation obtained

from the multiple regression analysis is

Chapter 7

150

EPSPISP 3.6784.13.27 −+= (7.4)

Where SP is maximum swell pressure, kPa,





between the measured and predicted values for the maximum swell pressure as

shown in Figure 7.29. Figure 7.30 shows the experimentally obtained maximum

swell pressure vs. the predicted values. The regression analysis of this prediction

models gives R2 value of 0.9437.

0

20

40

60

80

100

120

140

15 20 25 30 35 40 45 50 55

Plasticity Index, %

Max

imum

sw

ell p

ress

ure,

kP

a



maximum swell pressure.

Chapter 7

151

R 2 = 0.9437

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140Actual maximum swell pressure, kPa

Pre

dict

ed m

axim

um s

wel

l pre

ssur

e, k

Pa

Figure 7.30 The relation between measured and predicted maximum swell

pressure.

7.2.4.3 Reduction in free swell, swell pressure and dry unit weight

The reductions in free swell, swell pressure and dry unit weight due to EPS

inclusion are shown in Figures 7.31, 7.32 and 7.33 for soils SB16, SB24 and

SB32, respectively.

SB16

Dry unit weight

Maximum free swell

Maximum swell pressure

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1EPS, %

% R

educ

tion

Figure 7.31 Reduction in maximum swell pressure, maximum free swell and dry unit weight for SB16.

Chapter 7

152

SB24

Dry unit weight

Maximum free swell


0

10

20

30

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1EPS, %

% R

educ

tion

Figure 7.32 Reduction in maximum swell pressure, maximum free swell and dry

unit weight for SB24.

SB32

Dry unit weight

Maximum free swell


0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1EPS, %

% R

educ

tion

Figure 7.33 Reduction in maximum swell pressure, maximum free swell and dry

unit weight for SB32.

Chapter 7

153

Wibawa and Rahardjo (2001) noted that for clayey soils, swell pressure reaches

its peak at the optimum moisture content but decreases towards the dry and wet

sides of the optimum. They attributed this reduction to the specific surface area of

the soil particles. Specific surface area is defined as the area of liquid-vapour

interfacial around the soil particles per unit bulk volume of the soil. The specific

surface area has the greatest value at the maximum dry unit weight condition and

hence, in this state the soil absorbs the largest amount of water. When compared

with the dry unit weight at the optimum moisture content, the dry unit weights are

lower in the dry and wet sides of the optimum. A lower dry unit weight

corresponds with lower values of specific surface area and swell pressure. In the

present context, with the addition of EPS the dry unit weight of the composite is

significantly reduced, thus lowering the swell pressure and free swell

considerably.

Figure 7.34 Variation of maximum free swell with maximum dry unit weight for

different soils.

The variation of free swell and swell pressure with maximum dry unit weight

(possible variation indicated) obtained with the addition of EPS beads is shown in

Figures 7.34 and 7.35, respectively. It should be recalled that maximum dry unit

Chapter 7

154

weight decreases with increasing EPS content. From the Figures 7.34 and 7.35 it

can be observed that with a reduction in dry unit weight there is a reduction in

both free swell and swell pressure.

Figure 7.35 Variation of swell pressure with maximum dry unit weight for different soils.

Free swell

Swell pressure

0

20

40

60

80

100

120

140

10 12 14 16 18 20 22 24 26

Bentonite in SWEPS mixes, %

Free

sw

ell,

% o

r Sw

ell p

ress

ure,

kP

a

Figure 7.36 Variation of free swell and swell pressure with decrease in bentonite.

Chapter 7

155

In Chapter 6 (Figure 6.9), it was observed that as the EPS content increases, the

soil volume decreases that results in a corresponding reduction in swell pressure.

As bentonite is a visible indicator of swelling in the present study, its reduction

with the addition of EPS or sand is noticeable. For example, it can be observed

from Figure 7.36 that with reduction in bentonite fraction in SWEPS mixes there

is reduction in maximum free swell and maximum swell pressure. The reduction

can be due to sand and/or EPS beads replacing the bentonite and consequently

reduction in specific surface area of swelling fraction.

7.3 Cyclic swelling

As described in Chapter 3, expansive soils generally occur in arid and semi-arid

climatic zones where alternate wet and dry seasons are most common. Hence, the

soils are affected by the seasonal swell-shrink potential which are rather cyclic in

nature. The periodic swelling and shrinkage of expansive soils and the associated

movements of structures may result in cracking and fatigue (refer to Figure 3.2).

In a cyclic swelling test, a soil specimen is wetted and allowed to swell and then

dried to its initial moisture content (or less) at room temperature (or exposed to

direct sun light), then wetted again to swell, dried once more, and so on (Al-

Homoud et al., 1995). In some cases accelerated drying was also adopted (Allam

and Sridaharan, 1981; Subbarao and Satyadas, 1987, Rao et al., 2001)

Many researchers have conducted laboratory investigations to understand the

problem of cyclic swelling and shrinkage of clays. However, there remain some

contradictions on the observed behaviour of expansive soils in cyclic swelling and

shrinkage. Chu and Mou (1973), Chen et al. (1985), Chen and Ma (1987),

Subbarao and Satyadas (1987) and Dif and Blumel (1991), Al-Homound et al.

(1995), Basma et al. (1996) and Bilsel and Tuncer (1998) reported that when clay

specimens were repeatedly subjected to full swell from their initial moisture

content or specimen thickness, the clays showed signs of fatigue and thus

exhibited less expansion with each cycle. On the contrary, some other researchers

such as Popesco (1980), Osipov et al. (1987), and Day (1994) observed that

magnitude of swell increased with the number of wetting and drying cycles when

soil specimens were allowed to fully shrink to a moisture content equal to or less

than the shrinkage limit.

Chapter 7

156

All previously indicated studies, however, noted that expansion reaches an

equilibrium state after about 3 to 5 cycles. According to some researchers (Chu

and Mou, 1973; Osipov et al., 1987; Day, 1994; Al-Homound et al., 1995), this is

because cyclic wetting and drying of natural expansive soils leads to

rearrangement of soil particles, alterations in particle size and breakage of bonds

at particle contacts that in turn affect their swell-shrink behaviour.

Rao et al. (2001) studied the effect of cyclic wetting and drying on the index

properties of lime-stabilised expansive soil. They concluded that cyclic wetting

and drying have showed changes in index properties due to partial to near

complete breakdown in microstructure of the lime-stabilised soil specimens. This

indicates that even lime stabilised expansive soils undergo some changes due to

cyclic swell-shrink.

On sand-bentonite mixes, a review of the existing literature shows that most

investigators focussed on their engineering properties which included hydraulic

conductivity (Chapius, 1990, Mollins et al., 1996), permeability and

compressibility behaviour (Pandian et al., 1995), drained shear strength (Mollins

et al., 1999) and swelling behaviour (Sivapullaiah et al., 1996, Komine and Ogata,

2000). However, the influence of cyclic wetting and drying on the properties of

sand-bentonite mixtures was not studied. In practice, sand-bentonite mixes used as

a hydraulic barrier, for example, may undergo cyclic wetting and drying due to

moisture content variations.

In the present study, the influence of cyclic swell-shrink on sand-bentonite

composite was studied. Furthermore, the influence of EPS beads on the cyclic

behaviour of sand-bentonite mixes was also investigated. According to Rao et al.

(2000) and Tripathy et al. (2002), the wetting-induced deformations of compacted

expansive soils become nearly constant and the swell-shrink paths are reversible

once the soil reaches equilibrium, which is generally after about four to five

cycles of wetting and drying. Hence, the laboratory wetting-drying procedure in

the present study was terminated after 5 cycles of wetting and drying. Tests were

only conducted on SB24 and SB32 specimens because these two SB mixes fall

within the high and very high plasticity classification, respectively.

Chapter 7

157

7.3.1 Testing procedure

Past studies used conventional oedometer ring (commonly 75 mm in diameter and

19 mm in thickness) for studying the cyclic swell-shrink movements in clays.

However, in the present case California Bearing Ratio (CBR) mould was selected

for studying cyclic swell-shrink of sand-bentonite mixes since the recycled EPS

beads were up to 9.5 mm in size.

SWEPS specimens were compacted statically in three equal layers to the

maximum Proctor unit weight in CBR moulds. The diameter of the specimen was

kept at 152 mm but the height was reduced to 38 mm (i.e., diameter/height ratio =

4, similar to oedometer ring).

The inside of the CBR mould was smeared with silicone grease to minimise the

friction between the specimen and the mould. After compaction, Whatman No. 1

filter papers were placed at the top and bottom of the specimen. Subsequently, the

stem and perforated plate were placed on top of the specimen and surcharge

weights were placed on the perforated plate. A seating pressure of 2.9 kPa

(standard CBR surcharge pressure) was applied, while a dial gauge was placed on

the top of the stem for measuring the swelling deformation. The mould containing

the test specimen was subsequently submerged in water and dial readings were

taken at regular intervals. The setup is shown in Figure 7.37.

Figure 7.37 Cyclic swelling test setup with CBR moulds.

Chapter 7

158

In the previous studies (Day, 1994; Al-Homoud et al., 1995), cyclic swelling tests

were performed using conventional oedometer rings. In that case the test setup

had to be dismantled periodically to dry the specimen to the initial moisture

conditions. Thus shrinkage did not occur under constant pressure.

In the present case, to avoid disintegration, the specimen was kept in the mould at

all times while cyclic swelling and shrinkage tests were performed. By doing this,

the same pressure was applied while the specimen was undergoing repeated cycle

of swelling and shrinkage. Swelling behaviour was observed under ambient

temperature and shrinkage measured under temperature controlled conditions as

explained in the next subsection.

It should be noted that generally, in the field, cyclic swelling and shrinkage occurs

while the overburden pressure acts on top of the soil. Complete swelling and

shrinkage may not be reached because of weather conditions, limited moisture

variations, excessive layer thickness, etc. Hence, while the cyclic swelling and

shrinkage test in the current study did not produce a full swelling and shrinkage

values, it would replicate the field conditions more closely.

7.3.2 Method of wetting and drying

Wetting of samples was carried out by water immersion as shown in Figure 7.37.

The free swell was measured using the dial gauge mounted on the top of the stem

for at least 14 days as was done in swelling studies with oedometer. After

undergoing the first swelling, the CBR mould containing the specimen was

carefully taken out from the water chamber, wiped dry on the outside and the

increase in moisture content from the initial value was determined. Thereafter, the

specimen was dried for shrinkage determination.

With regards to drying, Allam and Sridharan (1981) used an accelerated drying

method by keeping the specimens at 110° C for 3 days while studying the effects

of cyclic wetting and drying on the shear strength of clays. However, as 110° C

was considered too severe for the EPS beads (see Chapter 4), the specimens were

kept at 60° C untill the moisture content reached the initial moisture content value.

Note that, as per ASTM D 559 – 03, these accelerated drying conditions are also

Chapter 7

159

applicable to compacted soil-cement mixtures to study the effect of wetting and

drying.

While undergoing drying, it was observed that the specimen’s outer surfaces were

drier than its inner part. These were generally reflected in the moisture content

readings. This moisture difference would make the specimen’s outer part swell to

a greater extent upon re-wetting until moisture content became uniform

throughout the specimen. To avoid this, once taken out from the oven, before

allowing for subsequent cycles of swelling, the top and bottom of the cylindrical

specimen were covered with a polythene sheet and the specimen was kept in a

humid chamber for 48 hours to equilibrate the moisture across the entire

specimen.

All the specimens underwent the same sequence of wetting and drying process.

As the specimens were allowed to dry, shrinkage occurred in both in radial

(horizontal) and vertical directions. In agreement with Day (1994), in this present

case the radial (horizontal) shrinkage was not considered because with each wet

cycle the clay specimen swelled back to its original diameter of 152 mm.

7.3.3 Variation of free swell with number of cycles

Figures 7.38 and 7.39 show the variation of maximum free swell based on

hyperbolic analysis for SB24 and SB32 respectively with increasing number of

cycles. SB24 shows a peak in first cycle and thereafter shows decrease in

maximum free swell with an increase in cycle number for all EPS contents,

whereas SB32 shows a peak at the second cycle and a decrease in free swell

thereafter. The influence of 0.3% EPS has no major effect on the free swell for

SB32 soil after the second cycle. This may be due to the presence of high

bentonite content in the mix.

Overall, it can be observed that the EPS inclusion has a specific influence on the

cyclic free swell of sand-bentonite mixtures. However, whatever the trend

followed by soil specimens without EPS beads is simply reflected in EPS

amended soils for SB32 soils.

Chapter 7

160

SB240.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

10

20

30

40

50

60

0 1 2 3 4 5 6

Cycle Number

Max

imum

free

sw

ell,

%

Figure 7.38 Variation of maximum free swell with increasing cycles for SB24.

SB320.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6

Cycle number

Max

imum

free

sw

ell,

%

Figure 7.39 Variation of maximum free swell with increasing cycles for SB32.

Furthermore, the results are not in agreement with the literature findings that soil

reaches equilibrium after 4 to 5 cycles. This may be due to the presence of voids

Chapter 7

161

in the sand particles and the rearrangement of clay particles within these voids

may be still continuing.

7.4 Effect of EPS and lime on swelling

While the addition of EPS beads reduces the magnitude of free swell; it lowers the

strength of the composite. In this case, results of the scoping studies with dredged

soil (Chapter 4) indicate that to enhance the strength of EPS amended dredged

soil, chemical stabilisers may be needed.

The addition of chemical stabilisers has been done in the past. For example, the

use of fly ash in fibre treated soils was investigated by Kaniraj and Havangi

(1998) and Punthutaecha et al. (2006). Furthermore, to improve the performance

of EPS amended dredged soils, Miki (1996) and Satoh et al. (2001) used lime and

cement as chemical stabilisers. Keeping this in view, limited studies were

conducted on the combined effect of hydrated lime and EPS on the free swell and

swell pressure of expansive soils.

For this purpose, a reconstituted soil of medium plasticity (SB24) was selected to

represent the average plasticity found in most locations (refer to Figure 5.1). The

lime was mixed at optimum lime content (OLC) as described in Chapter 5. For

SB24 the OLC was 4.4% by dry weight of soil.

This study was not intended to assess the effect of curing time. Hence, accelerated

curing time, as suggested by Thompson (1970), was adopted for the lime-

stabilised SWEPS specimens. For that purpose, the specimens were kept at 48.5°

C for 48 hours after compaction to replicate the effect of 28 days curing under

ambient conditions.

Figure 7.40, shows the variation of maximum free swell with and without lime

addition. From the figure, it can be observed that the combined treatment with

lime and EPS has reduced the free swell to 0%. This can be attributed to the ion

exchange and flocculation of clay particles due to the lime addition and partial

soil replacement by recycled EPS beads.

Chapter 7

162

SB24

Without lime

With lime

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

EPS, %

Max

imum

free

sw

ell,

%

Figure 7.40 Variation in maximum free swell with and without lime at various EPS

contents.

SB24, 0.0% EPS

Without lime

With lime (12%)

0

5

10

15

20

25

30

35

40

45

50

0 5000 10000 15000 20000 25000Time, min

Fre

e sw

ell,

%

Experimental data Hyperbolic fitExperimental dataHyperbolic fit

Figure 7.41 Variation of free swell with time, with and without lime addition for 0%

EPS content.

Chapter 7

163

SB24, 0.3% EPS

Without lime

With lime (12%)

0

5

10

15

20

25

30

35

40

0 5000 10000 15000 20000 25000

Time, min

Fre

e sw

ell,

%

Experimental dataHyperbolic fitExperimental dataHyperbolic fit

Figure 7.42 Variation of free swell with time, with and without lime addition for 0.3%

EPS content.

SB24

With lime

Without lime

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1EPS , %

Max

imu

m s

wel

l pre

ssu

re, k

Pa

Figure 7.43 Variation of maximum swell pressure with and without lime at various

EPS contents.

The variation of free swell with time is presented in Figures 7.41 and 7.42 for

0.0% and 0.3% EPS contents, respectively. From these figures it can be observed

that the magnitude of free swell is reduced considerably with the addition of lime.

Chapter 7

164

The influence of EPS beads on the swell pressure, with and without lime, is

shown in Figure 7.43. From the figure it is seen that the combined stabilisation

with lime and EPS beads reduce the swell pressure considerably. For example, the

swell pressure without any additives is 100 kPa. This is reduced to 3 kPa with the

addition of 4.4% of lime and 0.9% EPS at optimum lime content. In absolute

terms this reduction is 97%. The method of stabilisation with EPS beads and lime

is clearly very effective since swelling has mostly been eliminated.

7.5 Shrinkage characteristics

The magnitude of swell of soils is usually measured by means of swelling studies

as described in the previous sections. However, in addition to swelling, shrinkage

also plays a significant role in expansive soils. Since expansive soils exhibit

volumetric increase when water is added, they also undergo shrinkage through

volumetric reduction when the water is removed or extricated from the clay

crystal lattice upon desiccation.

For assessing the desiccation crack potential in expansive soils or compacted clay

liner/cover systems, volumetric shrinkage tests were generally conducted (Daniel

and Wu, 1993; Ziegler et al., 1998; Albrecht and Benson, 2001; Osinubi and

Nwaiwu, 2006). As explained in Chapters 3, shrinkage induces cracking of the

soil and increase the hydraulic conductivity. Furthermore, shrinkage cracking in

expansive soils followed by heaving usually results in distress to pavements and

foundations because of the ingress of moisture through superficial shrinkage

cracks (Kodikara et al., 1999; Puppala et al., 2004). Similar to swelling, shrinkage

also depends on the presence of expanding lattice minerals and their dispersion in

the soil mass.

To study the shrinkage potential or cracking behaviour of soils, researchers and

practitioners often use either a linear shrinkage strain test or Atterberg limit tests

or both (Puppala et al., 2004). Generally, the shrinkage potential of compacted

soil specimens can be measured using linear shrinkage bar tests (AS 1289.3.4.1,

1995). It should be noted that the thickness of shrinkage specimen influences the

magnitude of specific shrinkage (Sorochan, 1991). While various dimensions

Chapter 7

165

have been used in the past, Australian Standards specify a mould with 250 mm

internal length and 25 mm internal diameter.

Since the size of the recycled EPS beads was large in relation to the size of the

linear shrinkage mould, the test could not be performed in the usual way. Instead,

the shrinkage characteristics of SB mixes and SWEPS mixes were studied by

means of a three-dimensional volumetric shrinkage test using a standard

compaction mould. A test procedure similar to that of Puppala and Musenda

(2000), Puppala et al. (2004), Punthutaecha et al. (2006) was followed in the

current study. The method was different from that used by other researchers

(Daniel and Wu, 1993; Albrecht and Benson, 2001; Osinubi and Nwaiwu, 2006;

Oren et al., 2006) since the soil specimen was in a slurry form (at liquid limit)

rather than at optimum moisture content.

While this slurry (liquid limit) state may not represent the real field conditions or

the possible compaction moisture levels, the test method would provide a better

view on the variations in volume change behaviour and the corresponding effects

on soil properties due to the addition of modifiers/stabilisers (Puppala et al., 2004;

Punthutaecha et al., 2006).

7.5.1 Testing procedure

In this procedure, initially sand and bentonite were proportioned and mixed with

distilled water to form a slurry (at the appropriate liquid limit) and cured for a

minimum of 14 days for conditioning. To this slurry soil, recycled EPS beads

were then added in the required quantities by dry weight of soil and mixed until a

uniform and consistent mixture was obtained. Even though the specific gravity of

the recycled EPS beads is less than the specific gravity of the soil, no significant

settlement or segregation of EPS beads was observed in the slurry at all EPS

dosage levels.

The mixture was then slowly transferred into a standard compaction mould of 105

mm diameter and 115 mm height and lightly tamped to avoid the formation of air

voids. Each specimen was kept inside the mould at room temperature for 4 hours

for initial drying and subsequently oven dried at 70o C for 48 hours. During

Chapter 7

166

drying, the mould containing soil specimen was weighed regularly, and turned

over or rotated to let the soil specimen shrink uniformly. When mass of the mould

and specimen became constant, the volume change was determined by using a

digital vernier calliper.

The volumetric shrinkage strain of the specimen was calculated by using the

average values of the diameters and heights obtained at different locations.

Extreme care was taken in measuring the heights and diameters of the specimen to

avoid disturbance. Similar procedures were performed on soils with and without

EPS for all the three cases of SB16, SB24 and SB32.

The following equations (Equation 7.5 to 7.7) were used for the calculation of

axial, diametral and volumetric shrinkage strains of each specimen:

100(%) xH

HH

i

fia ��

�

��

� −=ε (7.5)

100(%) xD

DD

i

fid ��

�

��

� −=ε (7.6)

100(%) xV

VV

i

fiv ��

�

��

� −=ε (7.7)

Where aε = axial shrinkage strain, %

dε = diametral shrinkage strain, %

vε = volumetric shrinkage strain, %

Hi = initial height of specimen, m

Hf = final height of specimen, m

Di = initial diameter of specimen, m

Df = final diameter of specimen, m

Vi = initial volume of specimen, m3

Vf = final volume of specimen, m3

Note: The initial dimensions of the specimen were taken as the Proctor mould

dimensions.

Chapter 7

167

7.5.2. Shrinkage of SB mixes

The variations of volumetric shrinkage strain with the increase in bentonite

content are shown in Table 7.1 for the reconstituted expansive soils along with the

axial and diametrical strain values.

Table 7.1 Shrinkage characteristics of SB mixes.

Bentonite,

%

Liquid

limit,

%

Plasticity

index,

%

Axial

shrinkage,

%

Diametral

shrinkage,

%

Volumetric

shrinkage,

%

16 43 22 5.02 5.68 15.51

24 60 38 8.91 7.14 21.45

32 77 53 11.59 12.38 32.13

From the table, it can be observed that with increase in bentonite content, there

was an increase in all types of shrinkage. This is in agreement with the findings of

Sorochan (1991). He observed that the volumetric shrinkage is a function of the

quantity of colloidal particles with expanding lattice structure present in the soil.

Similarly, Albrecht and Benson (2001) have observed that volumetric shrinkage

strain increases with increasing clay content and Plasticity Index. They attributed

this to the greater affinity for water by the higher clay content due to higher

surface area. Hence, during drying stages greater quantity of water is removed

from soil mass. The same is also evidenced in the present case. All the sand-

bentonite composites were compacted at their liquid limits. With increasing

bentonite content and consequent increase in specific surface area, there is an

increase in liquid limit. That means, as the quantity of bentonite is increased, the

water holding nature of the composite is also increased. During drying, water is

removed thereby inducing a greater shrinkage in soils with higher bentonite

contents.

7.5.3 Shrinkage of SWEPS mixes

Figures 7.44, 7.45 and 7.46 show the variations in the axial, diametral and

volumetric shrinkage strains of the SWEPS mixes consisting of SB16, SB24 and

SB32 for all four EPS contents, respectively. From the figures it can be observed

Chapter 7

168

that the addition of EPS beads considerably reduces the magnitude of shrinkage of

expansive soils. The higher the quantity of EPS beads in the mix, the lesser is the

shrinkage.

The average volumetric shrinkage values of SB16, SB24 and SB32 are around

15%, 21% and 32%, respectively, as given in Table 7.1. In most cases, increasing

EPS content corresponds to decreasing shrinkage in the mix. For example, for

SB16 mix, with the addition of 0.3%, 0.6% and 0.9% EPS contents, in percentage

terms, the volumetric shrinkage reduced to around 15%, 36% and 50%

respectively, of the original volumetric shrinkage of the soil without EPS beads

Similarly, for SB24 mix the reduction in percentage terms corresponds to around

8%, 25% and 33% for 0.3%, 0.6% and 0.9% respectively. Similar reduction is

also observed for SB32 mix.

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40


Axi

al s

hrin

kage

, %

Figure 7.44 Variation of axial shrinkage with bentonite content and % EPS.

Chapter 7

169

0.3% EPS

0.6% EPS0.9% EPS

0.0% EPS

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40Bentonite content, %

Dia

met

ral s

hrin

kage

, %

Figure 7.45 Variation of diametral shrinkage with bentonite content and % EPS.

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40Bentonite content, %

Vol

umet

ric s

hrin

kage

, %

Figure 7.46 Variation of volumetric shrinkage with bentonite content and % EPS.

The change in the magnitude of shrinkage of the expansive soil can be attributed

to two mechanisms that occur with the addition of EPS beads. Firstly, the EPS

beads reduce the quantity of the expansive soil in the mix to a certain extent (i.e.

Chapter 7

170

partial soil replacement). This would ultimately lead to lesser soil available for

shrinkage. Secondly, the EPS is compressible in nature. Thus, in a confined state,

when soil swelling occurs, the EPS beads would compress to take care of the

increase in confinement stresses. On the other hand, when soil shrinkage occurs,

the EPS would expand with the decrease in confinement stresses - this would

result in a reduced shrinkage. Furthermore, the shrinkage of a soil mix depends on

the stiffness of the larger particles in the mix. When the particles are soft like the

EPS beads, an increase in shrinkage can be expected. However, because the

addition of EPS reduces the amount of soil that contributes to the shrinkage, this

eventually results in the reduction of the shrinkage.

7.5.4 Comparison with published literature

From the literature it is noticed that there are conflicting conclusions on the

influence of polymeric material like fibres on the reduction in volumetric

shrinkage potential of expansive soils.

Ziegler et al. (1998) studied the influence of short polymeric fibres on crack

development in clays. They prepared ten synthetic soil mixtures, by using 15%

kaolinite and varying the amount of sodium bentonite and calcium bentonite,

which produced plasticity indices ranging from 25 to 100%. The volume change

and cracking test was done by compacting soil specimens of 100 mm diameter

and 116 mm height into a standard Proctor mould to 95% of maximum dry unit

weight. Four fibre content levels were studied. They are 0%, 0.1%, 0.3% and a

few specimens with 1.0%. For each specimen, volume changes were recorded at

the end of last drying cycle. The percent volume change was determined as the

ratio of the total volume change to initial volume as followed in the present study.

Their test results indicated that the inclusion of fibres had no consistent effect on

the swell-shrink characteristics. They observed that the volumetric strain results

were rather scattered and it was on the order of 11 ± 8% for specimen with

plasticity indices greater than 40. Furthermore, they mentioned that the inclusion

of fibres has no noticeable effect on the percent volume change as the specimen

goes through wet and dry cycles.

Chapter 7

171

With regards to fibre reinforced soils, Puppala and Musenda (2000) mentioned

that the reduction in shrinkage potential was due to the tensile reinforcement

offered by the fibres in soils. However, in addition to tensile reinforcement, fibres

would also provide partial volumetric replacement of soil particles. Even though

fibres were added in small quantities they occupied substantial proportion of total

volume. In the present case, in terms of volumetric replacement, EPS beads had

more significant effect than fibres due to its much lower density; however, its

relatively low tensile strength would only have limited effect on the swelling

characteristics of the soil.

Albrecht and Benson (2001) stated that the volumetric shrinkage strain of a soil is

inversely proportional to the dry unit weight (weight of solids / volume of soil). In

other words, the higher the dry unit weight of the soil is, the lesser the volumetric

shrinkage will be. However, in the present case this observation is not valid

because the addition of EPS beads to the soils causes a reduction in both the unit

weight and the volumetric shrinkage of all mixes. Furthermore, Albrecht and

Benson (2001) indicated that the volumetric shrinkage strain occurring in

compacted clays during desiccation is a direct function of the saturated volumetric

moisture content (volume of water / total volume of soil). This statement is

applicable to the present case since the addition of EPS beads reduces the

available volume of water in the total volume of specimen and thus the shrinkage

strain.

Punthutaecha et al. (2006) conducted three-dimensional shrinkage strain tests on

two expansive soils treated with class F fly ash, bottom ash and fibres. The fibres

used were polypropylene fibres and nylon fibres. They observed that by

increasing the percentage of ash stabilisers, there was a reduction in volumetric

shrinkage strain potential. In addition, both polypropylene and nylon fibres also

decreased the shrinkage strains. They observed that the maximum decrease was at

0.2% fibre content, and at higher dosage levels the shrinkage strains reached a

plateau condition. They attributed the decrease in shrinkage strains due to fibre

treatments to strength, in particular, cohesion property enhancements that resulted

from the inclusions of fibres. The increase in apparent cohesion was found to be

indirectly related to the enhancement of tensile strength of the soils which in turn

Chapter 7

172

provided more resistance towards tensile forces exerted on the soils specimens

during shrinkage tests. Moreover, they observed that stabilisation with fibres

worked better in soils with higher fines content.

Punthutaecha et al. (2006), further, studied the effect of combined stabilisation

with fly ash and fibres on the volumetric shrinkage strain potential of the same

expansive soils. They observed that all combined stabiliser treated soils (either fly

ash with fibres or bottom ash with fibres) yielded lower shrinkage strains of 13%

to 20% when compared with control soils average shrinkage strains of around

30%.

In contrast to the above findings, results from the present study indicate that with

an increase in EPS content there was always a decrease in the volumetric

shrinkage strain of the soils. There was no plateau condition observed. With an

increase in fines content, more significant shrinkage reduction was obtained due

to EPS inclusion when compared with control soils (Table 7.2). Furthermore, the

shrinkage reduction was mostly attributed to partial soil replacement rather than

strength enhancement as was achieved through fibre addition.

Table 7.2 Reduction in volumetric shrinkage strain with the addition of EPS, %.

Mixes EPS

content, % SB16 SB24 SB32

0.0* -- -- --

0.3 15.73 8.39 22.12

0.6 35.98 24.66 34.14

0.9 50.16 33.19 48.86

* control soils

7.5.5 Predictive model for volumetric shrinkage

The volumetric shrinkage behaviour of SWEPS mixes was examined by focussing

on the influence of the soil type (PI of 22, 38 and 53%) and EPS content (0.0, 0.3,

0.6 and 0.9%).

Chapter 7

173


by correlating volumetric shrinkage with PI and EPS. The equation obtained from

the multiple regression analysis is

EPSPIVS 37.1139.01.8 −+= (7.8)

Where VS is volumetric shrinkage, %,





between the measured and predicted values for the volumetric shrinkage as shown

in Figure 7.47. Figure 7.48 shows the experimentally obtained volumetric

shrinkage vs. the predicted values. The regression analysis of this prediction

models gives R2 value of 0.9484.

0

5

10

15

20

25

30

35


Vol

um

etric

shr

inka

ge, %



volumetric shrinkage.

Chapter 7

174

R 2 = 0.9484

0

10

20

30

0 10 20 30Measured volumetric shrinkage, %

Pre

dict

ed v

olum

etri

c sh

rink

age,

%

Figure 7.48 The relation between measured and predicted volumetric shrinkage.

7.6 Summary

In keeping with the main focus of this research, recycled EPS beads were assessed

for their suitability as a swell-shrink modifier in reconstituted expansive soils. It

was observed that the inclusion of non expansive materials such as EPS beads to

the expansive soil can reduce the swell-shrink potential to some considerable

extent because of soil replacement effect and the reduction in total specific surface

area of clayey particles. Moreover, as the recycled EPS beads can compress or

expand depending on the forces exerted on them by the surrounding soil, the free

swell, swell pressure and shrinkage deformation can be reduced significantly. The

factors responsible for reduction are as detailed below.

(i) Reduction in dry unit weight

Unlike other chemical additives EPS has no cations to replace in the clay soil.

Instead, its physical structure makes the composite lighter thus there would be

reduction in dry unit weight. It is known that swelling is reciprocal to dry unit

weight (Wibawa and Rahardjo, 2001). As the EPS inclusion reduces the unit

weight of the mix, there will be a reduction in free swell, swell pressure and

shrinkage.

Chapter 7

175

(ii) Reduction in clay particles

Swelling of clay generally occurs because of the water adsorption between clay

particles. During water imbibition by clay soils, there could be instability of some

structural units of the particle rigidity and the breakage of particle contact bonds.

This can result in the swelling of the bulk soil volume as the water, being polar

liquid, accumulates over the increased particle surface area (Wilding and Tessier,

1988). Hence if the surface area is reduced this could potentially reduce the

swelling. The addition of EPS beads reduces the clay’s particle surface area

through the reduction of soil particles and hence there is a reduction in swelling.

(iii) Compression and expansion of EPS beads

Swelling of expansive soils generates compressive forces on the EPS beads. These

forces will be absorbed by the elastic nature of EPS beads. This creates a

neutralising effect and thus the volume of the soil mass remains little affected by

the water absorption. When the full compression of EPS is achieved, no further

EPS contraction can take place; this in turn will allow the soil to swell.

It is possible that under high compressive stresses the EPS beads are compressed

such that they effectively become polystyrene pieces. The compressed EPS beads

would then act as randomly distributed fibres in the soil which can resist further

deformation.

(iv) Thermal insulation of EPS beads

The thermal characteristics of SWEPS mixes were not studied in the present

research. However, it is known that increasing temperature causes moisture to

diffuse to cooler areas beneath pavements and buildings which results in swelling.

Because of the excellent thermal insulation qualities of EPS, thermal variation

within SWEPS mixes may be reduced. Consequently, swelling may also reduce.

Even though recycled EPS beads had proved to be a good modifier of swell-

shrink potential, the use of EPS beads with soil necessitated a study on the

influence of EPS beads on strength characteristics of soil. Chapter 9 therefore

describes the results of characterisation tests using direct shear and triaxial

machines.

Chapter 7

176

177

CHAPTER 8 - SHEAR STRENGTH OF SWEPS MIXES

The evaluation of the shear strength characteristics of geotechnical materials

represents an important part in the design and analysis of foundations, retaining

walls and earth slopes (Zou, 2001). In addition to evaluating the potential

effectiveness of recycled EPS beads as a swell-shrink modifier in expansive soils

as discussed Chapter 7, the EPS beads were further investigated in order to

understand their effects on the shear strength of the soil.

Even though EPS is not expected to improve the shear strength of expansive soils

because of their compressibility as was observed from UCS tests in scoping

studies with a dredged soil (Chapter 4), the shear strength characteristics of

SWEPS mixes were studied to understand their overall strength characteristics.

In general, the shear strength parameters, as prescribed by consideration of the

principles of soil mechanics, can be obtained in the laboratory from either the

direct shear test or the triaxial test. In this chapter, the behaviour of SWEPS mixes

under consolidated-drained direct shear and unconsolidated-undrained triaxial

conditions is described. In addition, a number of factors which may influence the

test results are also presented.

Direct shear tests were conducted prior to triaxial testing to investigate the

influence of EPS content on the shear strength and compressibility of the soil. The

shear strength parameters i.e. internal friction angle and cohesion were obtained

from both tests and subsequently analysed. In addition, the effect of lime on the

shear strength of SWEPS is also described for SB24 mix.

8.1 Direct shear tests

The shear box is one of the simplest laboratory equipment used to measure soil

shear strength. In the current study, for determining the shear strength of the

SWEPS mixes, the test was conducted according to the Australian Standard

AS1289.6.2.2-1998, “Determination of shear strength of a soil – direct shear test

using a shear box”.

Chapter 8

178

The shear box test setup used in this study is shown in Figure 8.1. The equipment,

as supplied by Wykeham Farrance, U.K., can accommodate 60 mm × 60 mm

specimen size.

Figure 8.1 Direct shear apparatus used the present study.

The normal stress on the specimen was applied using dead weights. The shear

force, applied to the specimen via an electric motor, was measured using a

proving ring. A dial gauge with a maximum travel of 15 mm was used to measure

the horizontal displacement (shear displacement) to a precision of ± 0.01 mm.

Another dial gauge with a maximum travel of 12 mm was employed to measure

the vertical displacement of the specimen to a precision of ± 0.002 mm.

The use of a standard direct shear apparatus brings certain inherent limitations.

For example, this limits the amount of EPS beads that can be added to the soil. In

addition, other problems such as the predetermined plane of shear failure,

ambiguous nature of effective stresses and strains, and the end effects in such a

small specimen make it more difficult to model soil-fibre (Yetimoglu, 2003) or

soil-EPS mixes behaviour realistically. Moreover, it is doubtful if complimentary

shear stresses acting on planes parallel to the axis of the specimen would result in

uniform stresses and strains (Tigchelaar et al., 2000).

Chapter 8

179

Notwithstanding these limitations, direct shear device has been widely used for

different theoretical and practical research projects in most laboratories all over

the world due to its simplicity, ease of operation and being an inexpensive and

practical test (Krishnaswamy and Raghavendra, 1989; Athanasopoulos, 1997;

Izgin and Wasti, 1998; Wasti and Ozduzgun, 2001; Yetimoglu and Salbas, 2003).

The device has also been employed in research elsewhere, to highlight the

complexity of fibre-reinforced soil behaviour (Gray and Ohashi, 1983) and soil-

tyre mixtures (Ghazavi and Sakhi, 2005).


Shear box tests were carried out to obtain the shear strength parameters of the

reconstituted expansive soils (SB16, SB24 and SB32) over four EPS contents

(0.0%, 0.3%, 0.6% and 0.9% by dry weight of soil). Considering that the objective

of the present investigation was to establish the effect of EPS inclusion on the

shear strength characteristics of the as-compacted (unsaturated) SWEPS mixes,

specimens were not saturated or submerged in water. However, consolidation was

performed before shearing the specimen.

The tests were performed at vertical pressures 25, 50 and 100 kPa. The strain rate

was set at 0.3 mm/min in all the tests. This slow rate of shear was determined

from the rate at which the specimen consolidates under the normal load which

was applied to the hanger, as suggested in AS 1289.6.2.2-1998. This test was a

consolidated drained shear test. Applied shear force, as displayed by the proving

ring, was recorded together with the resulting horizontal displacement up to a total

displacement of 8 mm to capture the post-failure behaviour.

As was performed for all other tests, in the present case all the specimens with and

without EPS beads were prepared by static compaction in three equal layers, as

described in Chapter 5, at their respective maximum dry unit weight and optimum

moisture content values as obtained in Chapter 6. Each layer was scarified before

adding the next for proper bonding.

In order to minimise the wall friction, the inside of the shear box was smeared

with silicone grease. To avoid the formation of a weak plane, care was taken to

Chapter 8

180

ensure that the top of the first compacted layer did not coincide with the boundary

between the two halves of the shear box.

8.1.2 Test results

The results of the direct shear tests are analysed in this section in terms of primary

settlement under normal load, shear and volumetric deformation behaviour, peak

shearing resistance of soils with and without EPS inclusion.

8.1.2.1 Primary settlement under normal load

Before performing shear deformation, each specimen was allowed to settle under

a given normal stress until there was no more change in the vertical displacement

readings. The compression of the specimen before shearing was observed for

specimens with and without the addition of EPS beads. For this purpose the

compression was carried out for 48 hours and the final settlement values are

shown in the Figures 8.2 (a), 8.2 (b) and 8.2 (c) for SB16, SB24 and SB32

respectively.

From the figures it can be observed that with increasing EPS content, due to the

compressive and deformability nature of EPS beads, the primary settlement

increases. This settlement was observed across all soil types. Furthermore, it can

also be observed that the magnitude of primary settlement depends on the applied

normal load. The higher the vertical load, the higher the settlement of the SWEPS

mix.

Figures 8.3, 8.4, 8.5 and 8.6 show the variation of the primary settlement at

different bentonite contents for 0.0%, 0.3%, 0.6% and 0.9% EPS contents

respectively. From these figures it can be observed that the magnitude of primary

settlement increases with increasing bentonite contents owing to increasing fines

content up to 0.6% EPS content. However, at 0.9% EPS content, the settlement

decreases for 25 kPa and 50 kPa normal loads and increases for 100 kPa normal

load.

Chapter 8

181

SB16

25 kPa

50kPa

100 kPa

0

1

2

3

0 0.2 0.4 0.6 0.8 1EPS, %

Set

tlem

ent,

mm

(a)

SB24

25kPa

50kPa

100 kPa

0

1

2

3

0 0.2 0.4 0.6 0.8 1EPS. %

Set

tlem

ent,

mm

(b)

SB32

25kPa

50 kPa

100kPa

0

1

2

3

0 0.2 0.4 0.6 0.8 1EPS, %

Set

tlem

ent,

mm

(C)

Figure 8.2 Variation of primary settlement of SWEPS mix with EPS at different

normal loads for (a) SB16, (b) SB24 and (c) SB32.

Chapter 8

182

0.0% EPS

25 kPa50 kPa

100 kPa

0

1

2

3


Set

tlem

ent,

mm

Figure 8.3 Variation of primary settlement with bentonite content at 0.0% EPS content.

0.3% EPS

25 kPa

50 kPa

100 kPa

0

1

2

3


Set

tlem

ent,

mm


0.6% EPS

25 kPa

50 kPa

100 kPa

0

1

2

3


Set

tlem

ent,

mm


0.9% EPS

25 kPa

50 kPa

100 kPa

0

1

2

3


Set

tlem

ent,

mm


Chapter 8

183

This can be attributed to the maximum dry unit weight of the soils. It can be

recalled that the dry unit weight of SB16, SB24 and SB32 are 17.07, 17.26 and

16.97 kN/m3 respectively (Table 5.6).

8.1.2.2 Stress – strain behaviour

Figures 8.7 to 8.15 show the variation of shear stress with shear displacement and

also variation of vertical displacement with shear displacement for all the three

soils SB16, SB24 and SB32 at 0.0%, 0.3%, 0.6% and 0.9% EPS contents at

various normal stresses.

It can be observed from these figures that the variations of shear stress and

vertical displacement were influenced significantly by the addition of EPS beads

for all the soils. Results indicate that the shear stress increased with increasing

shear displacement as exhibited in figures and reached a peak at around 1 to 2 mm

of shear displacement in almost all the cases irrespective of EPS content (Table

8.1). The variation on peak shear stress with EPS contents at various normal

stresses is presented in Table 8.2.

Table 8.1 Shear displacement at peak shear stress at various normal stresses

Soil EPS %

Shear displacement (mm) at normal stress of 25 kPa 50 kPa 100 kPa

SB16

0.0 1.0 1.2 0.7 0.3 0.7 1.1 1.6 0.6 1.0 1.4 1.8 0.9 0.9 4.9 4.8

SB24

0.0 0.5 0.9 1.1 0.3 0.7 0.9 1.2 0.6 0.8 0.9 1.7 0.9 0.7 0.7 3.3

SB32

0.0 0.4 0.6 0.5 0.3 0.4 0.8 1.1 0.6 0.8 0.6 1.8 0.9 1.0 2.5 3.0

Chapter 8

184

Table 8.2 Variation of peak shear stress with normal stress.

Peak shear stress (kPa) at normal stress of Soil type EPS, %

25 kPa 50 kPa 100 kPa

SB16 0.0 26.7 42.0 82.5

0.3 39.2 55.0 91.3

0.6 53.4 70.0 105.8

0.9 45.0 62.5 96.7

SB24

0.0 60.8 88.8 129.6

0.3 64.1 71.5 117.8

0.6 49.8 70.2 102.5

0.9 50.6 102.5 102.3

SB32

0.0 91.1 110.3 168.1

0.3 71.0 98.5 145.0

0.6 63.5 89.0 126.3

0.9 57.7 77.4 116.8

In general, the peak shear stress tends to decrease with increasing EPS content;

however, the trend is not consistent. SB16 showed an increase in peak shear

stress whereas SB24 and SB32 showed decrease in peak shear stress. This could

be due to the increase in fines fraction in SB24 and SB32 mixes.

Dilation occurred in SWEPS mixes in most cases except for specimens under

100kPa normal stresses, where some compression was noticed during the initial

stages. For these specimens, subsequent shearing produced dilation which was not

as high as those obtained under other normal stresses.

Furthermore, it was also noted that the dilation was higher in specimens with

lower EPS contents. This may be related to the fact that there was more

compression of EPS beads during shearing, thereby decreasing dilation.

Furthermore, there could be voids in the specimen due to EPS inclusion. Hence,

during shearing, specimens with higher EPS contents produced less dilation. This

could also be related to less dry unit weight of SWEPS mixes.

Chapter 8

185

SB160

10

20

30

40

50

60

0 2 4 6 8Shear displacement, mm

She

ar s

tres

s, k

Pa

0.0% EPS, 25 kPa0.3% EPS, 25 kPa0.6% EPS, 25 kPa0.9% EPS, 25 kPa

SB16

0

10

20

30

40

50

60

70

80


She

ar s

tres

s, k

Pa


(a) (a)

SB16

-0.20

0.20.40.60.8

11.21.41.61.8


Ver

tical

dis

plac

emen

t, m

m

0.0%, 25 kPa0.3%, 25 kPa0.6%, 25 kPa0.9%, 25 kPa

SB16-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8

Shear displacement, mmV

ertic

al

disp

lace

mnt

, mm

0.0%, 50 kPa0.3%, 50kPa0.6%, 50 kPa0.9%, 50 kPa

(b) (b )

Figure 8.7 Direct shear results for SB16 at 25 kPa normal stress, Figure 8.8 Direct shear results for SB16 at 50 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.

Chapter 8

186

SB16

0

20

40

60

80

100

120


She

ar s

tres

s, k

Pa

0.0% EPS, 100 kPa0.3% EPS, 100 kPa0.6% EPS, 100 kPa0.9% EPS, 100 kPa SB24

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7Shear displacement, mm

She

ar s

tres

s, k

Pa

0.0% EPS, 25 kPa0.3% EPS, 25 kPa0.6% EPS, 25kPa0.9% EPS, 25 kPa

(a) (a)

SB16-0.2

0

0.2

0.4

0.6

0.8

0 2 4 6 8


Ver

tical

di

spla

cem

ent,

mm

0.0%, 100 kPa0.3%, 100 kPa0.6%, 100 kPa0.9%, 100 kPa

SB24-0.5

0

0.5

1

1.5

2

2.5

0 2 4 6 8


Ver

tical

di

spla

cem

ent,

mm

0.0% EPS, 25kPa0.3% EPS, 25 kPa0.6% EPS, 25kPa0.9% EPS, 25 kPa

(b) (b)


Chapter 8

187

SB24

0

20

40

60

80

100


She

ar s

tres

s, k

Pa


SB24

0

20

40

60

80

100

120

140


She

ar s

tres

s, k

Pa

0.0% EPS, 100kPa0.3% EPS, 100kPa0.6% EPS, 100 kPa0.9% EPS, 100kPa

5 (a) 6 (a)

SB24-0.2

00.20.40.60.8

11.21.41.61.8

0 2 4 6 8Shear dispalcement, mm

Ver

tica

l d

isp

lace

men

t, m

m

0.0% EPS, 50 kPa0.3% EPS, 50kPa0.6% EPS, 50 kPa0.9% EPS, 50 kPa

SB24-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4


Ver

tical

di

spla

cem

ent,

mm


5 (b) 6 (b)


Chapter 8

188

SB32

0102030405060708090

100


She

ar s

tres

s, k

Pa

0.0% EPS, 25 kPa0.3% EPS, 25 kPa0.6% EPS, 25kPa0.9% EPS, 25 kPa

SB320

20

40

60

80

100

120


She

ar s

tres

s, k

Pa

0.0% EPS, 50 kPa0.3% EPS, 50kPa0.6% EPS, 50 kPa0.9% Eps, 50 kPa

7 (a) 8 (a)

SB32

0

0.5

1

1.5

2

2.5


Ver

tical

di

spla

cem

ent,

mm

0.0% EPS, 25kPa0.3% EPS, 25kPa0.6% EPS, 25kPa0.9% EPS, 25kPa

SB32-0.5

0

0.5

1

1.5

2

2.5

0 2 4 6 8

Shear displacement, mmV

ertic

al

disp

lace

men

t, m

m

0.0% EPS, 50kPa0.3% EPS, 50 kPa0.6% EPS, 50 kPa0.9% EPS, 50 kPa

7 (b) 8 (b) Figure 8.13 Direct shear results for SB32 at 25 kPa normal stress, Figure 8.14 Direct shear results for SB32 at 50 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.

Chapter 8

189

SB32

020406080

100120140160180


She

ar s

tres

s, k

Pa

0.0% EPS, 100kPa0.3% EPS, 100kPa0.6% EPS, 100kPa0.9% EPS, 100kPa

(a)

SB32-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8


Ver

tical

di

spla

cem

ent,

mm

0.0% EPS, 100kPa0.3% EPS, 100kPa0.6% EPS, 100 kPa0.9% EPS, 100kPa

(b)

Figure 8.15 Direct shear results for SB16 at 100 kPa normal stress, (a) Shear stress vs. shear displacement and

(b) Vertical displacement vs. shear displacement.

Chapter 8

190

For shearing to occur along the horizontal failure plane, two reasons can be

possible. That is soil particles have to either shear around or shear into the EPS

beads and/or EPS bead failure. Because of the compressible or deformable nature

of EPS beads, soil particles would probably fail along the soil-bead interfaces

during shearing. In these circumstances, the path of least resistance will determine

the shear strength. The following explanation postulates the failure of EPS beads

in soil-EPS mixes.

When a normal stress is applied to the SWEPS specimen, EPS beads may initially

start to compress. It is because the EPS beads are more compressible than the soil

particles for the same load. During this course, soil will also undergo some

settlement and rearrangement. Once the EPS beads have reached their full

compressibility, soil particles start to penetrate into the compressed EPS beads.

This can be followed by the rearrangement of soil particles.

In the Figures 8.7 to 8.15, the curves of shear stress vs. shear displacement show

some irregularities / discontinuities. These can be attributed to the fact that EPS

beads were randomly located on the failure plane, thus contributing to the

fluctuations of resistance against shear. The extent of these discontinuities seemed

to be a function of EPS content (more intensive at higher EPS contents).

Based on the observed behaviour, the compression of EPS beads and its effect of

the shear strength characteristics may be postulated as follows. During shearing

EPS beads will start deforming into ellipsoidal shape. As shearing continues, the

beads will take form as a strip and eventually fail. The compression of EPS beads

as postulated in Figure 8.16 might have occurred in all SWEPS specimens.

Figure 8.16 Postulated shear failure mechanism of EPS beads.

Chapter 8

191

Figures 8.17 to 8.19 show the variation of shear stress with shear displacement

with respect to bentonite content for a particular EPS content at various normal

stresses.

0.3% EPS, 25 kPa

0

20

40

60

80

100

0 2 4 6 8Shear displacement,mm

She

ar s

tres

s, k

Pa

SB16SB24SB32

(a)

0.3% EPS, 50 kPa

0

20

40

60

80

100

120


She

ar s

tres

s, k

Pa

SB16SB24SB 32

(b)

0.3% EPS, 100 kPa

020406080

100120140160180


She

ar s

tres

s, k

Pa

SB16SB24SB32

(c)

Figure 8.17 Variation of shear stress and shear displacement with 0.3% EPS for

different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa.

Chapter 8

192

0.6% EPS, 25 kPa

0

10

20

30

40

50

60

70


She

ar s

tres

s, k

Pa

SB16SB24SB32

(a)

0.6% EPS, 50 kPa

0

20

40

60

80

100


She

ar s

tres

s, k

Pa

SB16SB24SB32

(b)

0.6% EPS, 100 kPa

0

20

40

60

80

100

120

140


She

ar s

tres

s, k

Pa

SB16SB24SB32

(c)

Figure 8.18 Variation of shear stress and shear displacement with 0.6% EPS for different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa.

Chapter 8

193

0.9% EPS, 25 kPa

0

10

20

30

40

50

60


Sh

ear

stre

ss, k

Pa

SB16SB24SB32

(a)

0.9% EPS, 50 kPa

0

10

20

30

40

50

60

70

80

90


She

ar s

tres

s, k

Pa

SB16SB24SB32

(b)

0.9% EPS, 100 kPa

0

20

40

60

80

100

120

140


She

ar s

tres

s, k

Pa

SB16SB24SB32

(c)

Figure 8.19 Variation of shear stress and shear displacement with 0.9% EPS for

different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa.

From these figures it can be observed that for a constant EPS content, the peak

shear strength increases with an increase in bentonite content. This can be

attributed to the increase in cohesion created by the bentonite in the mix.

Chapter 8

194

Chalermyanont and Arrykul (2005) noticed similar behaviour and wrote that

cohesion increased from 0 to 24.9 kPa with an increase in bentonite from 0 to 9%.

8.1.2.3 Shear strength parameters of SWEPS mixes

By plotting the peak shear stress versus the applied normal stress for various

reconstituted soils (Figures 8.20, 8.21 and 8.22 for SB16, SB24 and SB32,

respectively); the shear strength parameters (cohesion intercept and friction angle)

were determined according to the Mohr-Coulomb criterion. The figures also show

the failure envelopes for various mixes.

The cohesion intercept (c) and friction angle (φ) were determined by performing

linear regression to obtain the best fitting straight line through the measured data

points. The regression analysis indicated that the shear envelopes of soil with and

without EPS inclusion are linear with varying cohesion intercepts (the correlation

coefficients are almost equal to unity in all cases). The resulting variations in

cohesion and angle of internal friction for SB16, SB24 and SB32 are shown in

Figures 8.23 and 8.24 respectively.

SB16

0.0% EPS0.3% EPS

0.6% EPS0.9% EPS

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140Normal stress, kPa

Pea

k sh

ear

stre

ss, k

Pa

Figure 8.20 Variation of shear stress with normal stress for SB16.

Chapter 8

195

SB24 0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

Normal stress, kPa

Pea

k sh

ear

stre

ss, k

Pa


SB32

0.0 % EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

30

60

90

120

150

180

0 20 40 60 80 100 120 140 160Normal stress, kPa

She

ar s

tres

s, k

Pa


The variation of c and φ due to EPS inclusion is not consistent. In general, EPS

inclusion tends to reduce the shear strength when the bentonite content is

relatively high. The cohesion decreases with an increase in EPS content for SB24

and SB32, whereas the opposite is true for SB16. It could be due to the improved

Chapter 8

196

bonding between the sand fraction in SB16 mix and the EPS beads thus resisting

the shearing.

These variations could be also due to prevailing drainage conditions or variations

in drainage conditions. Interparticle contact could be higher in SB16 than other

SB mixes. It is known that for clayey soils, some unknown amount of

consolidation could occur during shear, which would give a larger shear strength

than usual, as is noticed in the present case. However, addition of EPS beads

makes the settlement to occur in EPS beads first followed by the soils, thereby

reducing the cohesion.

From the above it can be observed that EPS is merely acting as soil replacement

filler. Zou (2001) observed that for an EPS specimen with a density of 20 kg/m3,

the angle of internal friction was 6.4° and the cohesion intercept was 42.6 kPa. As

EPS has low angle of internal friction and cohesion than soils, its inclusion

correspondingly influence the cohesion and angle of internal friction of the

SWEPS mixes. However, in the Figures 8.23 and 8.24, a lot of scattering can be

observed with respect to the influence of EPS on shear strength parameters, which

can be attributed to the interface conditions and the relatively small specimen size.

SB16

SB24

SB32

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1EPS, %

Coh

esio

n, k

Pa

Figure 8.23 Variation of cohesion with EPS.

Chapter 8

197

SB16

SB24

SB32

30

32

34

36

38

40

42

44

46

48

0 0.2 0.4 0.6 0.8 1

EPS, %

Ang

le o

f int

erna

l fric

tion,

o

Figure 8.24 Variation of angle of internal friction with EPS.

The maximum EPS bead size is 9 mm which is 15% of the length of the test

specimen and 22.5% of the height of the test specimen. Even though beads of this

size only exist in small percentage within the composite, they are randomly

distributed and may be present at the failure plane. This and other limitations of

the direct shear tests described earlier such as imposition of failure plane etc.

clearly had some effects on the shear strength characteristics of the SWEPS

mixes. Hence, the shear strength of the mixes was further studied using triaxial

equipment as described in the ensuing section.

8.2 Unconsolidated-Undrained triaxial tests

Unconsolidated-Undrained (UU) triaxial tests are most commonly done on

samples of earth-fill materials which are compacted in the laboratory under

specified conditions of moisture content and dry unit weight (Bishop and Henkel,

1962). Moreover, with ordinary triaxial equipment it is not possible to determine

accurately the effective stresses in unsaturated soil specimens, so the common

practice is to conduct undrained triaxial tests on unsaturated specimens and

measure only the total stress (Das, 2005).

Chapter 8

198

Generally, the shear strength of highway materials is often characterised by using

unconfined compression tests. However, according to Rauch et al. (2002), testing

in a triaxial cell yields a more reliable measure of strength than unconfined

compression tests. This is especially true for fissured and compacted soils, where

the confining pressure keeps the specimen intact under load (Rauch et al., 2002).

Furthermore, UU testing has been adopted by many investigators for testing soil

with other additives. For example, Krishnaswamy and Srinivasulu Reddy (1989),

Rogers and Lee (1994), Pradhan et al. (1995), Kayabali (1997), Muntohar (2000)

Kaniraj and Havanagi (2001), Pandian and Krishna (2002), Rauch et al. (2002),

Prabhakar and Sridhar (2002), Minegashi et al. (2002), Kaniraj and Gayathri

(2003) and Yoonz et al. (2005) have performed UU tests to establish the strength

characteristics of soils stabilised with fibres, geotextiles or other chemical

stabilisers. Considering that the objective of the present investigation was to

establish the effect of EPS inclusion on the shear strength characteristics of the as-

compacted (unsaturated) SWEPS mixes, UU test was subsequently adopted.

While other triaxial test types (Consolidated Drained (CD) or Consolidated

Undrained (CU)) will produce more meaningful strength parameters, the UU test

carried out in the present study was intended as a ranking test. The values of

cohesion and internal friction so obtained demonstrate the effects of EPS on the

strength characteristics of the mixes.

It should be noted that initially, it was planned to perform the Consolidated

Drained (CD) test. However, during the course of the testing program it was

observed that there were some practical limitations in using bentonite as a main

component for the triaxial specimens. Because bentonite was mixed with fine

sand in very high proportions, specimen saturation became very difficult. Even

with a considerable increase in back pressure, the time taken to achieve complete

saturation was excessive. As a large number of specimens had to be tested, it was

decided to perform UU tests on reconstituted soil with and without recycled EPS

beads. Notwithstanding its limitations, the test would give an indication as to what

extent the addition of EPS beads would alter the characteristics of the

reconstituted expansive soil.

Chapter 8

199

8.2.1 Testing scheme

The triaxial test setup used in this research is shown in the Figure 8.25. It consists

of a 50 kN Wykeham Farrance compression machine and a triaxial cell which has

been designed for testing soil specimens up to 100 mm diameter.

Figure 8.25 Triaxial testing equipment.

The test specimen was enclosed with a latex rubber membrane (0.3 mm thick) and

placed inside a Wykeham Farrance triaxial cell, which can withstand internal

pressure up to 1700 kPa. The applied load and vertical displacement can be read

manually by using a proving ring and a dial gauge, with a resolution of 10.5

Newtons and 0.01 mm, respectively. A GDS Standard 3 MPa Digital

Pressure/Volume Controller (STDDPC) accurate to the volume measurement of

1mm3 was used to regulate the cell pressure to a pre-set value.

Chapter 8

200

All triaxial tests were conducted at a constant axial strain rate of 0.15% / min

under UU conditions to simulate the behaviour of soils subjected to quick loading

immediately after construction.

Triaxial specimens were prepared for each of the three reconstituted soils (SB16,

SB24 and SB32) with EPS content of 0.0%, 0.3%, 0.6% and 0.9% by dry weight.

The test was conducted based on the Australian Standard AS 1289.6.4.1 (1998),

“Determination of compressive strength of a soil – Compressive strength of a

specimen tested in undrained triaxial compression without measurement of pore

water pressure”.

Test specimen

All the SB and SWEPS specimens used in this testing program were prepared

according to the procedure described earlier in Chapter 5 (Section 5.8).

Subsequently, the cylindrical specimens (200 mm H × 100 mm D) were

compacted in a three-part split brass mould to their respective maximum dry unit

weight and optimum moisture content. The inside of the mould was smeared with

a thin layer of silicon grease prior to compaction. Each specimen was compacted

in five equal layers using a Proctor hammer to the equivalent standard compactive

energy. The surface of each layer was scarified before compacting the next layer

to enhance bonding.

The triaxial tests in the current study were carried out at four different confining

stresses, which are 25 kPa, 50 kPa, 100 kPa and 200 kPa. The range of confining

pressure was chosen to obtain more well-defined and accurate plots of Mohr

envelopes.

To calculate the vertical stress on the tested specimen in a UU triaxial test,

corrections should normally be made for the average cross-sectional area of the

specimen for each recorded point of the test (AS 1289.6.4.1, 1998). Hence, the

cross-sectional area of each specimen was corrected using the axial strains on the

assumption that the specimen deform as a right cylinder and have zero volume

change.

Chapter 8

201

The parameters and variables in the testing program are presented in Table 8.3

and a set of SWEPS tested specimens is shown in Figure 8.26.

Table 8.3 Variables in triaxial testing.

Confining stress, kPa 25, 50, 100 and 200

Geometry, mm 200 mm height and 100 mm diameter

EPS ratio, % 0.0, 0.3, 0.6 and 0.9

Plasticity index of soil, %

Soil types

22, 38 and 53

SB16, SB24 and SB32

Displacement rate 0.5 mm/min

Stabiliser None and Hydrated lime

Figure 8.26 A set of SWEPS test specimens after being tested.

8.2.2 Stress –strain behaviour

Figures 8.27, 8.28 and 8.29 show the variation of the deviator stress with axial

strain and EPS contents for SB16, SB24 and SB32, respectively. Furthermore,

Figures 8.30, 8.31 and 8.32 present the variation of deviator stress with axial

strain and confining stresses for SB16, SB24 and SB32, respectively. The values

Chapter 8

202

of deviator stress at failure ( ) f31 σσ − and the corresponding failure strain, fε for

different confining pressures, 3σ are presented in Table 8.4, 8.5 and 8.6 for SB16,

SB24 and SB32, respectively.

According to AS 1289.6.4.1 (1998), loading on the specimen has to be continued

until either the maximum value of the load has been passed or an axial strain of

20% has been reached. In the present case, for all the tested specimens, maximum

value of the load was passed before the axial strain of 20% was reached. Hence

the same were considered for peak deviator stress.

From the figures it can be observed that the stress-strain curves of soils with and

without EPS contents are similar in shape and in most cases reach peak values at

relatively large strains. Furthermore, it can also be noted that the addition of EPS

beads does not enhance the strength of the SB mixes. In fact, with an increase in

EPS content the strength noticeably decreases.

The results, for all mixing ratios, are a reduction in peak deviator stress with

increasing EPS content. This decrease can be explained as follows. The soil grains

are intact and can take care of loading through rearrangement of voids in between

the soil particles. However, EPS compressive strength at a density of 20 kg/m3 is

around 98 kPa (Zou, 2001). Hence, as the loading is increased, EPS beads

compress along with the rearrangement of soil particles thereby decreasing the

deviator stress. In addition, the initial tangent Young’s modulus decreases with

increasing EPS content for all soils types (Figures 8.33 to 8.35). However, the

advantage of EPS inclusion in soil is that the strain to attain the peak deviator

stress increases with increasing EPS content i.e. the addition of larger amount of

EPS beads makes the mix more ductile. This increase in ductility is shown in

Figure 8.27 to 8.29 by joining the peak deviator stresses in each figure with a

solid line (line of peaks).

Chapter 8

203

SB16, 25 kPa

0

50

100

150

200

250

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a

0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks

SB16, 50 kPa

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a


(a) (b)

SB16, 100 kPa

0

100

200

300

400

500

0 2 4 6 8 10 12 14

Axial strain, %

Dev

iato

r st

ress

, kP

a


SB16, 200 kPa

0

100

200

300

400

500

600

700

800

0 5 10 15 20Axial strain, %

Dev

iato

r st

ress

, kP

a


(c) (d)

Figure 8.27 Stress - strain curves at different EPS contents for SB16 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.

Chapter 8

204

SB24, 25 kPa

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a

0.0% EPS 0.3% EPS 0.6% EPS 0.9% EPSLine of peaks

SB24, 50 kPa

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16Axial strain, %

Dev

iato

r st

ress

, kpa

0.0% EPS 0.3% EPS 0.6% EPS0.9% EPSLine of peaks

(a) (b)

SB24, 100 kPa

050

100150200250300350400450500


Dev

iato

r st

ress

, kP

a

0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of Peaks

SB24, 200 kPa

0

100

200

300

400

500

600

700

800


Dev

iato

r st

ress

, kP

a


(c) (d)


Chapter 8

205

SB32, 25kPa

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12Axial strain, %

Dev

iato

r st

ress

, kP

a


SB32, 50 kPa

0

50

100

150

200

250

300

350


Dev

iato

r st

ress

, kP

a


(a) (b)

SB32, 100kPa

0

100

200

300

400

500


Dev

iato

r st

ress

, kP

a


SB32, 200kPa

0

100

200

300

400

500

600

700


Dev

iato

r st

ress

, kP

a


(c) (d)


Chapter 8

206

SB16, 0.0% EPS

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10Axial strain, %

Dev

iato

r st

ress

, kP

a

25kPa 50kPa100 kPa 200 kPaLine of peaks

SB16, 0.3% EPS

0

100

200

300

400

500

600

0 5 10 15Axial strain, %

Dev

iato

r st

ress

, kP

a

25kPa 50kPa100kPa 200kPaLine of peaks

(a) (b)

SB16, 0.6% EPS

0

100

200

300

400

500

0 3 6 9 12 15 18Axial strain, %

Dev

iato

r st

ress

, kP

a

25 kPa 50kPa100 kPa 200 kPaLine of peaks

SB16, 0.9% EPS

0

100

200

300

400


Dev

iato

r st

ress

, kP

a

25 kPa 50 kPa100 kPa 200 kPaLine of peaks

(c) (d)

Figure 8.30 Stress-strain response of SB16 at different confining pressures for EPS contents of

(a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.

Chapter 8

207

SB24, 0.0% EPS

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12 14 16 18Axial strain, %

Dev

iato

r st

ress

, kP

a

25 kPa 50 kPa100 kPa 200kPaLine of peaks

SB24, 0.3% EPS

0

100

200

300

400

500

600


Dev

iato

r st

ress

, kP

a


(a) (b)

SB24, 0.6% EPS

0

100

200

300

400

500

600


Dev

iato

r st

ress

, kP

a


SB24, 0.9% EPS

0

100

200

300

400

500

0 5 10 15 20 25Axial strain, %

Dev

aito

r st

ress

, kP

a


(c) (d)

Figure 8.31 Stress-strain response of SB24 at different confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.

Chapter 8

208

SB32, 0.0% EPS

0

100

200

300

400

500

600

700


Dev

iato

r st

ress

, kP

a

25kPa 50 kPa100 kPa 200 kPaLine of peaks

SB32, 0.3% EPS

0

100

200

300

400

500

600


Dev

iato

r st

ress

, kP

a


(a) (b)

SB32, 0.6% EPS

0

100

200

300

400

500


Dev

iato

r st

ress

, kP

a


SB32, 0.9% EPS

0

50

100

150

200

250

300

350


Dev

iato

r st

ress

, kP

a


(c) (d) Figure 8.32 Stress-strain response of SB32 at different confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.

Chapter 8

209

Table 8.4 Deviator stress ( ) f31 σσ − and strain ( fε ) at failure for SB16

3σ 0.0% EPS 0.3% EPS 0.6% EPS 0.9% EPS

( ) f31 σσ − fε ( ) f31 σσ − fε ( ) f31 σσ − fε ( ) f31 σσ − fε

kPa kPa % kPa % kPa % kPa % 25 237.40 3.50 199.82 6.00 149.85 8.50 122.21 9.50

50 312.90 5.25 255.30 9.50 216.00 10.25 176.50 12.00

100 439.70 7.75 390.95 9.75 306.80 11.00 263.40 12.25

200 696.30 6.75 551.00 12.75 432.40 16.25 352.30 17.50


3σ 0.0% EPS 0.3% EPS 0.6% EPS 0.9% EPS

kPa

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

25 304.00 3.75 252.13 5.00 212.79 8.00 141.90 10.00

50 373.70 5.25 304.20 6.75 222.65 8.75 179.40 10.25

100 460.85 7.25 377.98 10.25 298.94 13.00 268.20 15.00

200 679.10 10.5 557.27 14.50 488.96 18.00 405.03 19.00


3σ 0.0% EPS 0.3% EPS 0.6% EPS 0.9% EPS

kPa

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

( ) f31 σσ −

kPa

fε

%

25 303.40 5.25 281.27 6.50 237.33 8.50 177.02 9.00

50 337.17 6.25 324.85 9.00 267.13 10.00 220.70 11.25

100 429.58 10.25 373.69 14.00 315.40 13.75 273.15 15.75

200 581.85 14.50 554.19 15.75 468.78 17.50 325.00 16.75

Chapter 8

210

SB16

100 kPa

50 kPa

25 kPa

200kPa

0

50

100

150

200

250

300

350

400

450

0 0.2 0.4 0.6 0.8 1

EPS, %

Initi

al ta

nge

nt Y

oung

s m

odul

us, k

Pa

Figure 8.33 Variation of Initial tangent Young’s modulus with confining pressure

and EPS content for SB16.

SB24

25 kPa

50 kPa

100 kPa

200 kPa

0

50

100

150

200

250

300

350

400

450

500

0 0.2 0.4 0.6 0.8 1

EPS, %

Initi

al ta

ngen

t you

ngs

mod

ulus

, kP

a



Chapter 8

211

SB32

200 kPa

25 kPa

50 kPa

100 kPa

0

50

100

150

200

250

300

350

0 0.2 0.4 0.6 0.8 1

EPS, %

Initi

al ta

ngen

t you

ngs

mo

dulu

s, k

Pa



It can be observed from the Tables 8.4, 8.5 and 8.6 for SB16, SB24 and SB32

soils respectively, that for the same soil type with a specific EPS content,

increasing the confining stress results in an increase in peak deviator stress.

It is known that the initial tangent Young’s modulus increase with an increase in

confining pressure. The same trend was noticed in the present case for all SWEPS

specimens. However, this increase is more pronounced at 0.0% EPS content and

the difference in initial tangent Young’s modulus decreases with increasing EPS

content and confining pressure (Figures 8.33 to 8.35). This could be due to the

compression of EPS beads with increasing confining pressure.

Composite modulus was calculated based on the volume fraction of the EPS in

SWEPS mix from the equation of proportionality as per the following equations

Upper bound

EPSEPSSoilSoilc VEVEE += (8.1)

Lower bound

SoilEPSEPSsoil

EPSSoilc EVEV

EEE

+= (8.2)

Chapter 8

212

Where Ec is the initial tangent Young’s modulus of the composite, kPa

ESoil is the initial tangent Young’s modulus of soil, kPa

EEPS is the initial tangent Young’s modulus of EPS, kPa (in this case 6200

kPa)

VSoil is the volume fraction of soil in SWEPS mix,

VEPS is the volume fraction of EPS in SWEPS mix.

The resulting graph for SB16 at 25 kPa confining pressure is shown in Figure

8.36. However, it can be observed from Figures 8.33 to 8.35 that the experimental

values are lower than the lower bound values. It indicates that the composite

modulus based on the equation of proportionality is not suitable for the SWEPS

mixes. Each mix case has to be observed independently based on the mix design.

Figure 8.36 Calculated composite modulus for SB16 at 25 kPa confining pressure.

The composite modulus based on the Equations 8.1 and 8.2 are shown in Figures

8.37, 8.38 and 8.39 for SB16, SB24 and SB32 respectively.

Chapter 8

213

SB16, 25 kPa Upper bound

Lower bound

0

500

1000

1500

0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS

Mod

ulus

of

Ela

stic

ity, k

Pa Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points

(a) (b)


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa

Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa

Data points

(c) (d)

Figure 8.37 Calculated composite modulus for SB16 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.

Chapter 8

214


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa

Data points

(a) (b)


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa

Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points

(c) (d)


Chapter 8

215


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points

(a) (b)


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points


Lower bound

0

500

1000

1500


Mod

ulus

of

Ela

stic

ity, k

Pa Data points

(c) (d)


Chapter 8

216

8.2.2.1 Predictive model for initial tangent Young’s modulus

The multiple regression analysis of initial tangent Young’s modulus, EPS content

and soil type produced the following equation for the initial tangent Young’s

modulus.

3547.07.23621.015.171 σ+−+= EPSPIEti (8.3)

Where Eti is the initial tangent Young’s modulus in kPa,

PI is plasticity index of the soil in %,

EPS is EPS content in % and

3σ is the confining pressure in kPa.

Figure 8.40 The relation between measured and predicted initial tangent Young’s

modulus.

The Equation 8.3 is applicable for the range of soils tested in the present study. A

plot between the measured initial tangent Young’s modulus and the predicted

initial tangent Young’s modulus is shown in Figure 8.40.

8.2.3 Shear strength parameters

Peak major principal and minor principal stresses were used for the determination

of the total stress shear stress parameters from the UU triaxial tests. For each soil

type, an s-t plot (Whitlow, 2000) was used to determine the cohesion (c) and angle

of internal friction (φ), where

Chapter 8

217

( ) fs 3121 σσ += (8.4)

( ) ft 3121 σσ −= (8.5)

where 1σ = peak major principal stress, kPa

3σ = minor principal stress, kPa

At the point of failure, the Mohr circle touches the Mohr-Coulomb failure

envelope and thus alternative failure criteria is given by

αtansat += (8.6)

The parameters of this stress point failure criteria, a and α are related to those of

the Mohr-coulomb criteria as follows

αφ tansin = (8.7)

ac =αcos (8.8)

Figures 8.41 to 8.43 present the s-t plots for the UU tests showing the alternative

failure envelope. The variation of cohesion mobilized (cuu) and angle of internal

friction (φuu) with and without the addition of EPS beads for different soils is

shown in Figure 8.44. The subscript “uu” refers to the parameters derived from

UU test. Note that φuu > 0 as the test specimens were not saturated.

SB16

0.6% EPS0.9% EPS

0.0% EPS

0.3% EPS

0

100

200

300

400

500

600

0 100 200 300 400 500 600

s, kPa

t, kP

a

Figure 8.41 s-t plots for SB16.

Chapter 8

218

SB24

0.6% EPS0.9% EPS

0.0% EPS0.3% EPS

0

100

200

300

400

500

600

0 100 200 300 400 500 600

s, kPa

t, kP

a


SB32

0.9% EPS

0.0% EPS

0.3% EPS0.6% EPS

0

100

200

300

400

500

600

0 100 200 300 400 500 600s, kPa

t, kP

a


Chapter 8

219

(a)

(b)

(c)

Figure 8.44 Variation of cohesion (c) and angle of internal friction (φ) for different soils (a) SB16, (b) SB24 and (c) SB32.

Chapter 8

220

Figure 8.45 Typical failure modes of SWEPS mixes.

It can be observed from the Figure 8.44 that by increasing the EPS content, both

cohesion and angle of internal friction decrease for all SWEPS mixes. However,

the changes in c and φ for SB32 are relatively small, indicating that the effect of

EPS on the shear strength of highly plastic soil is not significant.

Typical failure modes of soils with and without EPS beads are shown in Figure

8.45. From the figure it can be observed that with increasing EPS content the

shape, inclination and roughness of the failure plane changes. Without EPS beads

the failure plane is fairly linear and short. However, with the addition of EPS

beads the failure plane increased in length. The inclination was observed to vary

from 62° to 56° for SB16, 60° to 57° for SB24 and 58° to 53° for SB32 from 0.0%

EPS to 0.9% EPS contents. The roughness of the failure plane increases with

increasing EPS content because the failure has to occur along the soil-EPS

interfaces.

Variation of cohesion and angle of internal friction for all SWEPS mixes at

different plasticity indices corresponding to the respective bentonite contents is

presented in Figures 8.46 and 8.47, respectively. It is known that cohesion

increases with increasing plasticity index and angle of internal friction decreases

with plasticity index. The similar trend was observed in the present study across

all EPS contents.

Chapter 8

221

0

10

20

30

40

50

60

70

80

90

100


Coh

esio

n, k

Pa


Figure 8.46 Variation of cohesion with EPS for different soils.

0

10

20

30

40

50

15 20 25 30 35 40 45 50 55

Plasticity Index, %

Ang

le o

f int

erna

l fric

tion,

o

0.0% Measured0.3% Measured0.6% Measured0.9% MeasuredRegression model

Figure 8.47 Variation of angle internal friction with EPS for different soils.

The nature of cohesion and angle of internal friction variations in SWEPS mixes

can be explained in the light of EPS characteristics. The tensile strength of EPS at

Chapter 8

222

a density of 20 kg/m3 is 200 kPa whereas compressive strength (based on 10%

strain criterion) is 100 kPa (Horvath, 1995). Furthermore, Zou (2001) observed

the angle of internal friction and cohesion for an EPS specimen of 20 kg/m3 under

UU test. The values were 8.6° and 42.6 kPa respectively. Therefore, it is not

surprising that this present study has found that as EPS replaces the soil fraction;

the cohesion decreases proportionally with %EPS because of the lower strength of

EPS beads when compared with the control soils. Since the EPS beads form weak

links within the soil matrix, failure has to occur either through compression,

slippage or tensile failure of the beads along the failure plane.

Similar behaviour was observed by Puppala et al. (2000) while carrying out

unconfined compressive strength (UCS) tests on specimens of expansive soils

reinforced with polypropylene fibres. It was observed that the use of a large

amount of fibres reduced the cohesive strength since the volume of soil was

decreased and the loss of cohesive strength was not compensated by the

polypropylene fibres reinforcement. Another reason was related to the lowering of

the compacted unit weight of the soils associated with the increase in fibre

dosages.

In a different study, while discussing the shear strength characteristics of clay-tyre

chip mixture, Edil (2004) mentioned that the strength of the clay was not

increased with the addition of tyre chips. He also stated that, in fact, adding tyre

chips resulted in a lower shear strength values at low normal stresses. It was

suggested that poor bonding between clay and tyre chips was the cause of the

problem. While the bond between the soil and EPS mixes in the present case may

have played a role, the compressibility of EPS beads has clearly reduced the shear

strength of the composite.

Minegashi et al. (2002) conducted a series of static loading UU triaxial

compression tests on a loam mixed with EPS beads and cement at confining

pressures of 50, 100, 150 and 200 kPa. They observed that the deviator stress or

the mobilised compressive strength increased with an increase in confining

pressure on, or after reaching an axial strain of about 5%. No noticeable peak

strengths were observed. They further observed that at confining pressures of

Chapter 8

223

more than 100 kPa, there was no distinct difference in the peak deviator strength

with the increase in beads content. Contrary to this observation, in the present

case there was a decrease in deviator strength with increasing EPS contents. This

could possibly be due to variation in soils moisture content, the type of EPS beads

used and EPS gradation.

In addition, as EPS beads are impermeable, excess pore water pressure may

develop more easily within the specimen. In a similar case, Ingold and Miller

(1983) mentioned that reinforcing clay specimens with continuous horizontal

layers of aluminium foil caused reductions in undrained compressive strength to

about 50%. Thus, in the present case, with increasing EPS contents there could be

a significant increase in pore water pressure in the SWEPS mix which eventually

leads to failure.

8.2.3.1 Predictive models for cohesion and angle of internal friction

The cohesion and angle of internal friction of SWEPS mixes was examined by

focussing on the influence of the soil type (PI of 22, 38 and 53%) and EPS content

(0.0, 0.3, 0.6 and 0.9%).


by correlating cohesion and angle of internal friction with PI and EPS. The

equation obtained from the multiple regression analysis is

EPSPIc 48.2694.045.32 −+= (8.9)

EPSPI 54.917.02.37 −−=φ (8.10)

Where c is cohesion, kPa,

φ is angle of internal friction, °



These equations are valid only for the range of soils tested and for EPS contents


between the measured and predicted values for the cohesion and angle of internal

Chapter 8

224

friction as shown in Figures 8.46 and 8.47. Figures 8.48 and 8.49 show the

experimentally obtained cohesion and angle of internal friction vs. the predicted

values respectively.

R 2 = 0.8852

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90

Measured cohesion, kPa

Pre

dict

ed c

ohes

ion,

kP

a

Figure 8.48 The relation between measured and predicted cohesion.

R 2 = 0.8188

0

5

10

15

20

25

30

35

40

0 10 20 30 40Measured angle of internal friction

Pre

dict

ed a

ngle

of i

nter

nal f

rict

ion

Figure 8.49 The relation between measured and predicted angle of internal friction.

8.2.4 Failure envelopes

Figure 8.50 shows the failure envelopes in principal stress space, namely the

variation of axial stress at failure �1f , with confining stress, �3, for SB16, SB24

and SB32 at different EPS contents.

Chapter 8

225

Generally, published results (Maher and Gray, 1990; Ranjan et al., 1996; Kaniraj

and Havanagi, 2001) showed that the addition of fibres resulted in a bilinear

failure envelope. This was attributed by Maher and Gray (1990) and Ranjan et al.

(1996) to the existence of a critical confining stress, critσ ; below and above which

there are two linear portions. They further noticed that the slope of the initial

linear portion is steeper than the second portion above the critσ . According to

Maher and Gray (1990), the initial linear portion was characterised by the pullout

failure of the fibres and the second linear portion was characterised by tensile

failure of the fibres.

In the present investigation, SWEPS mixes exhibited a single linear trend instead

of bilinear trend (Figure 8.43). Regression analysis of all the data points of each

envelope in the present case showed that for all the confining pressure ranges the

measured data points fitted well on a straight line which can be expressed as

1311 cmf += σσ (8.11)

where m1 and c1 are the slopes of the straight line and the intercept of the straight

line with the f1σ axis, respectively (Kaniraj and Gayathri, 2003). The results of

the regression analyses are presented in Table 8.7.

There are some reports in the literature where a linear relationship is observed.

For example, Foose et al. (1996) showed that failure envelopes for sand-tyre chip

mixtures are linear for loose sands and non-linear for dense sands. Similarly,

Tatlisoz et al. (1997) reported a linear failure envelope for the sandy silt-tyre chip

mixtures and non-linear envelope for sand-tyre chip mixtures. From these results

it may be inferred that fine grained soil composites tend to show a linear failure

envelope as what has been observed with the SWEPS composite of the current

study.

Andersland and Khattack (1979) performed tests on kaolinite clay reinforced with

cellulose pulp fibre. The shear strength under various testing conditions

(undrained, consolidated-drained and consolidated-undrained) increased with

increasing fibre content. The ductility of the specimen was also found to increase

Chapter 8

226

with increasing fibre content. The load transfer mechanism on the fibre soil

interface was explained as an attraction between soil particles and fibres.

SB160.3% EPS

0.6% EPS0.9% EPS

0.0% EPS

100

300

500

700

900

0 50 100 150 200 250Confining stress, kPa

Maj

or p

rinc

ipal

st

ress

, kP

a

(a)

SB240.3% EPS0.6% EPS0.9% EPS

0.0% EPS

100

300

500

700

900

0 50 100 150 200 250

Confining stress, kPa

Maj

or p

rinc

ipal

st

ress

, kP

a

(b)

SB32

0.6% EPS

0.9% EPS

0.0% EPS0.3% EPS

100

300

500

700

900

0 50 100 150 200 250Confining stress, kPa

Maj

or p

rinc

ipal

st

ress

, kP

a

(c)

Figure 8.50 Failure envelopes of (a) SB16, (b) SB24 and (c) SB32

at various EPS contents.

Chapter 8

227

Table 8.7 Regression coefficients from failure envelopes.

Soil EPS m1 c1 R2 value

SB16

0.0 3.600 177.82 0.999

0.3 3.008 161.02 0.993

0.6 2.564 129.61 0.992

0.9 2.277 108.84 0.987

SB24

0.0 3.102 257.13 0.998

0.3 2.721 211.52 0.999

0.6 2.639 152.18 0.992

0.9 2.508 107.21 0.998

SB32

0.0 2.608 262.24 0.999

0.3 2.539 239.14 0.995

0.6 2.323 198.11 0.996

0.9 1.802 173.77 0.986

Even though kaolinite was not used in the present case, the results showed that the

addition of EPS beads decreased the shear strength. However, ductility was

increased with the addition of EPS as was noticed with fibre added soils from the

previous study.

While stabilising expansive (black cotton) soils with fly ash mixes, Pandian et al.

(2001) have found that there was an optimum fly ash content, above which there

would be strength reduction with the addition of fly ash to the soil. In contrast, for

the present investigation, the optimum EPS content was not found because a

consistent decrease in the strength of the SWEPS mixes occurs with the addition

of EPS.

The shear strength of fibre-reinforced clay was more difficult to predict than that

of fibre-reinforced sand (Li, 2005). This was because of the difficulty in

quantifying the pore water pressure and consequently, the interface shear strength.

Chapter 8

228

Limited past research conducted on fibre-reinforced clay showed inconsistent

results regarding the shear strength increase due to fibre reinforcement (Li, 2005).

The fibre-clay interaction, investigated by Li (2005) using five fine grained soils

was found to be more complex than fibre-sand interaction. The shear strength was

found to be influenced by factors such as volume change, unit weight, compaction

water content, degree of saturation and strain levels. Even though these factors

were considered specifically in the present study, the above limitations could be

the reasons for the random variation of shear strength in the present results. For

example, unit weight, compaction water content and volume changes due to

compression of EPS beads might have influenced the shear strength results.

8.3 Effect of lime on the shear strength of SWEPS

As mentioned in Chapter 7, the effect of lime as a chemical stabiliser on the shear

strength of a SWEPS mix was investigated in addition to its effects on the

swelling characteristics. Due to the time constraint, only one reconstituted soil

was considered (SB24). The lime content was at optimum lime content and the

tests were conducted on the specimens after undergoing accelerated curing

conditions as described in Section 7.4. The variation of deviator stress with axial

strain and percentage of EPS for three different confining pressures is shown in

Figure 8.51. In addition, the variation of deviator stress with axial strain and

confining pressure for various EPS contents is shown in Figure 8.52.

The shear strength characteristics are similar to those of unstabilised SWEPS.

However, as expected, a significant increase in peak deviator stress was achieved

with the addition of lime as chemical stabiliser. In addition, it can also be

observed from the figures that by increasing the EPS contents the ductility of the

lime stabilised soils increased significantly. The lime stabilised soils took more

strain to reach failure with the EPS inclusion.

The s-t plots (Figure 8.53) were drawn for the lime stabilised SWEPS mixes.

Based on the y-intercept and slope of the modified failure shear envelopes, the

cohesion and angle of internal friction were calculated and compared with those

without lime in Figure 8.54 and 8.55, respectively.

Chapter 8

229

SB24, 50kPa, with lime

0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a

0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks

SB24, 100 kPa, with lime

0

300

600

900

1200

1500

1800

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a


(a) (b)

SB24, 200 kPa, with lime0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

, kP

a


(c)

Figure 8.51 Stress - strain curves at different EPS contents for lime-stabilised SB24 at confining pressures of (a) 50 kPa, (b) 100 kPa and (c) 200 kPa.

Chapter 8

230

SB24, 0.0% EPS, with lime

0

500

1000

1500

2000

2500

0 1 2 3 4 5Axial strain, %

Dev

iato

r st

ress

, kP

a

50 kPa100 kPa200 kPaLine of peaks


0

200

400

600

800

1000

1200

1400

1600

0 1 2 3 4 5 6 7Axial strain, %

Dev

iato

r st

ress

, kP

a


(a) (b)


0

200

400

600

800

1000

1200

0 2 4 6 8 10 12Axial strain, %

Dev

iato

r st

ress

, kP

a



0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14Axial strain, %

Dev

iato

r st

ress

,kP

a


(c) (d)

Figure 8.52 Stress-strain response of lime-stabilised SB24 at different confining pressures with (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.

Chapter 8

231

SB24 with lime

0.3% EPS

0.6% EPS

0.9% EPS

0.0% EPS

0

300

600

900

1200

1500

0 300 600 900 1200 1500

s, kPa

t, kP

a

Figure 8.53 s-t plots for SB24 with lime.

SB24

With lime

Without lime

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1EPS, %

Coh

esio

n, C

uu, k

Pa

Figure 8.54 Variation of cohesion with and without lime for SB24.

Chapter 8

232

SB24

With lime

Without lime

0

5

10

15

20

25

30

35

40

45

50

0 0.2 0.4 0.6 0.8 1

EPS, %

Ang

le o

f int

erna

l fric

tion,

o

Figure 8.55 Variation of angle of internal friction with and without lime for SB24.

As expected, addition of lime has increased the cohesion in the soil due to

pozzolonic reactions for the same EPS content. Similar trend was also observed

with respect to angle of internal friction. However, with increased EPS content,

even though lime was added, the cohesion and friction angles were decreased. As

described earlier this can be attributed to the replacement of soil particles by the

EPS beads which eventually reduced the shear strength of the composite.

Consoli et al. (1998) reported that fibre reinforcement increased the peak and

residual shear strength of cement treated soils, and reduced the brittleness. In the

present case, EPS beads increased the ductility as exhibited by the line of peaks.

However, the strength was not improved.

8.4 Summary

An experimental study was carried out to investigate the influence of recycled

EPS beads on the shear behaviour of reconstituted expansive soils by using both

direct shear test and triaxial shear tests.

Chapter 8

233

Direct shear apparatus was used to determine the influence of recycled EPS beads

on the shear response of the reconstituted soils. Three soil types and four EPS

contents by dry mass of soil were investigated. It was noticed that EPS beads

increased the initial settlement of the specimen under normal load. Dilation was

observed in soil-EPS mixes at high normal loads.

The SWEPS mixes are composed of two contrasting materials in terms of their

particle size and strength. The reconstituted soil is a clayey sand with high

plasticity whereas recycled EPS beads are coarser but have a smaller internal

friction angle. By their nature EPS beads are compressible. Hence, by combining

these two materials a different composite is produced. In this case, the addition of

EPS beads does not contribute a strength increase as was provided by some

fibrous compounds in soils.

EPS is different from other materials such as fibres, tyre chips etc., in the sense

that the latter materials have reasonably high tensile strength and consequently

can take care of much of the tensile stresses in the soil. However, EPS has a low

tensile stress. Moreover, with its elasticity, EPS can easily deform under loads,

therefore, reducing the strength of the composite considerably.

When used in the context of expansive soils, strength is not the only criterion. In

addition to strength, swelling also is a predominant factor to be considered. It has

been demonstrated that the while strength is not increased, inclusion of EPS beads

can reduce shrinkage and swelling potential of soil.

The range of results produced shows the high dependency of the behaviour of the

SWEPS mixes on the EPS content at the soils’ optimum moisture content. Hence,

each situation needs to be considered separately to arrive at a SWEPS mix

suitable for the site and soil conditions.

Following this shear behaviour of SWEPS mixes, another very important aspects

of expansive soils, suction and desiccation, were briefly investigated with the

inclusion of EPS beads. This is described in Chapter 9.

Chapter 8

234

One particularly useful property of SWEPS is its relatively high ductility, which

suits certain earth structure applications. Compacted soil liners used in final cover

systems, for example, must be sufficiently ductile to accommodate differential

settlement and must be resistant to cracking caused by moisture variations e.g.

desiccation (Qian et al., 2002). Chapter 10 will discuss the application of SWEPS

technology in landfills.

235

CHAPTER 9 - SUCTION AND DESICCATION STUDIES Since soil is a very complex material, the inclusion of additive(s) can cause

substantial, and sometimes unpredictable, alterations of its properties. In the

foregoing chapters, the influence of recycled EPS beads on the swelling (Chapter

7) and the strength characteristics of the reconstituted expansive soils (Chapter 8)

were discussed. In this chapter, the influence of EPS on suction and desiccation is

described.

9.1 Suction studies

Suction controls different properties of unsaturated soils such as strength, stiffness

hydraulic conductivity and desiccation. In order to understand the behaviour of

partially saturated soils, the suction in the soil must be measured (Bulut et al.,

2000; Skinner, 2000). The section describes the limited study performed in order

to assess the influence of recycled EPS beads on the suction of the reconstituted

expansive soils.

In engineering practice, soil suction consists of two components viz., osmotic

suction and matric suction (Fredlund and Rahardjo, 1993). Osmotic suction is

caused by the chemical activity and mineralogy of the soil. Specifically, osmotic

potential arises from variations in the salt content in the pore fluid from one point

to another. In contrast to osmotic suction, matric suction is usually ascribed to

capillary forces, soil texture and the air-water interface that exist in an unsaturated

soil. It is therefore strongly related to geometrical factors such as pore size and

shape (Houston et al., 1994). Total suction is a function of both osmotic and

matric suction.

Ridley (1993) defined matric suction as a measure of the energy required to

remove a water molecule from the soil matrix without the water changing its state

and total suction was defined as a measure of the energy required to remove a

water molecule from a soil matrix through evaporation.

Chapter 9

236

There are many direct and indirect measurement techniques available to establish

matric and total suctions in soils. For matric suctions, the direct methods include

the instruments used actually to measure the pore water suction, as in the case of

suction plate, the pressure plate, the pressure membrane apparatus, tensiometers,

the osmotic tensiometer and the Imperial suction probe. On the other hand, the

indirect techniques measure the intermediate parameter that can be related to

suction through a separate calibration or theoretical support, as in the case of filter

paper (in contact), porous blocks and thermal conductivity sensors (Ridley, 1993;

Montanez, 2002).

The total suction can be determined by measuring relative humidity. Measurement

techniques suitable to determine the total suction are the transmitter psychrometer,

the thermocouple psychrometer and the non-contact filter paper method (Ridley,

1993).

More thorough discussions on the concept, measurement and use of the suction

components have been presented by Fredlund and Rahardjo (1993). Additional

discussions on the use of suction in expansive soils are also available from

Johnson and Snethen (1978) and Snethen and Huang (1992)

Bulut et al. (2000) studied the comparison of total suction values from

psychrometer and filter paper methods for three different soils compacted well

above the optimum moisture content. They observed that both methods were

sensitive to suction changes at high moisture contents. However, from the

standard deviation results they concluded that the filter paper method gave more

consistent results.

Suction testing using filter paper on a routine basis is relatively inexpensive

(approximately the same cost as for natural moisture content) and provides

additional means of laboratory quality control (Houston et al., 1994).

Furthermore, Thompson and McKeen (1995) observed that in normal commercial

laboratories where the work is usually performed by engineering technicians,

reliable and consistent test data are obtained using the filter paper method. A

Chapter 9

237

thorough discussion on the use and calibration of filter papers for suction

measurements was presented by Leong et al. (2002).

The basic principle in this method is that the moisture content of the filter paper

comes into equilibrium with that of the soil specimen either through vapour flow

or liquid flow. Here the filter paper may be regarded as a suction sensor. At

equilibrium, the filter paper is allowed to absorb water through vapour flow from

the atmosphere surrounding the soil specimen in a non-contact method to measure

the total suction. However, if the filter paper is allowed to absorb water through

fluid flow by capillary effect, as in a contact method, then matric suction is

measured (Bulut et al., 2000). At equilibrium, soil suction is equal to filter paper

suction.

Based on their test results, Sibley and Williams (1990) suggested that Whatman

No. 42 filter paper was the most appropriate for use over the entire range of

suction investigated (0 to 100 MPa). Furthermore, Leong et al. (2002) stated that

the performance of Whatman no.42 filter paper was more consistent than other

types of filter papers. This filter paper was also found to be more consistent in

quality and have less hysteresis.

In the current research, soil suction determinations were made on reconstituted

soils with and without EPS beads through an indirect means by using ash-free

quantitative type Whatman No. 42 filter papers from the same batch, since it is the

only known technique which covers the full range of suction measurement (from

zero to perhaps 100 MPa) (Houston et al., 1994). Whatman No.42 filter paper has

shown to be a suitable adsorbent although other grades and types of filter papers

are also used (Gourley and Schreiner, 1995). Both total and matric suction

measurements are possible with this method. The test procedure is simple,

straightforward and does not require any special equipment (Leong et al., 2002);

however, proper care must be exercised in measurement.

9.1.1 Filter paper calibration relationships

The calibration curves relating soil suction moisture content of filter papers have

been established using filter papers, salt solutions, pressure plates and membranes,

Chapter 9

238

and tensiometers (Bulut et al., 2000). The salt solutions are usually used for high

suction ranges and the pressures plates and tensiometer are used for low suction

ranges.

Several relationships between filter paper (absorbent material) moisture content

and suction have been established for various types of filter papers such as Fisher

quantitative filter papers, Schleicher and Schuell filter paper, and Whatman filter

papers (McQueen and Miller,1968; Al-Khafaf and Hanks, 1974; Hamblin, 1981;

Chandler et al., 1992; Houston et al., 1994 and Leong et al., 2002).

For the Whatman No. 42 filter paper a number of calibration curves are presented

in Table 9.1. Leong et al. (2002) attributed the differences in calibration equations

to several factors viz., quality of filter paper, suction source used in calibration,

hysteresis and equilibration times. Based on the use of soil sample of ‘known’

suctions for calibration purposes, they suggested a set of equations for Whatman

No. 42 filter paper for different moisture contents. These equations were selected

for the current study to determine the matric and total suctions.

Table 9.1 Calibration curves for Whatman No.42 filter papers (after Leong et al., 2002).

References Calibration curves*

Hamblin (1981) log � = 8.022 - 3.683 log wf

Chadler and Gutierrez (1986) log � = 4.84 - 0.0622 wf wf < 47

Chadler et al. (1992) log � = 6.05 - 2.48 log wf wf � 47

Greacen et al. (1987) log � = 5.327 - 0.0779 wf wf < 45.3

ASTM (1997) log � = 2.413 - 0.0135 wf wf � 45.3

Leong et al. (2002) Matric suction

log � = 2.909 - 0.0229 wf wf � 47

log � = 4.945 - 0.0673 wf wf < 47

Total suction

log � = 8.778 - 0.222 wf wf � 26

log � = 5.31 - 0.0879 wf wf < 26

* Note : � = suction in kPa; wf = filter paper moisture content in %.

Chapter 9

239

9.1.2 Sample preparation for suction measurement

Bulut et al. (2000) cautioned that it is very important to maintain the contact

between filter paper and soil intimately enough in measuring matric suction so

that the transfer of soil water occurs through fluid flow but not through vapour

flow. With the addition of EPS, however, it was difficult to cut a SWEPS

specimen into two equal parts with an intimate contact surface. Hence, in the

present research, instead of cutting the specimen into two parts, two parts were

individually compacted statically at their respective MDD and OMC in a split

mould of 50 mm diameter and 100 mm height, in equal proportions.

The procedure used in the present study involves inserting an initially oven dried

filter paper (Whatman No.42) between the two halves of specimen. The filter

paper for measuring matric suction was sandwiched in between two other large

size protective filter papers to avoid the soil and electrical tape sticking to it

(ASTM D 5298, 2003). The joint between the two halves were subsequently

sealed with electrical tape as shown in Figure 9.1.

Leong et al. (2002) stated that the short test duration does not allow for bacterial

or algal growth on filter paper and suggested no treatment to the filter papers for

controlling the growth. Upon observation, no such algal or bacterial growth was

noticed in the current research.

The distribution of EPS beads at the interface of a typical specimen at different

EPS content is shown in Figure 9.2. Note that with an increase in EPS content the

soil area reduces.

Additionally, according to ASTM D 5298 (2003), two separate filter papers were

placed at the top of the same specimen on a PVC ring separator (used for support

and isolation of filter papers from the specimen) for measuring the total suction by

non contact method (Figure 9.3). The support was in such a form that produced

minimum contact with filter papers in order to prevent the transmission of

moisture into filter papers through the support. Furthermore, a small container

(see Figure 9.3) was used to ensure rapid equilibrium and to minimise the change

Chapter 9

240

in moisture content of the specimen, and hence the soil suction (McQueen and

Miller, 1968).

Figure 9.1 Specimen preparation for suction measurement.

Figure 9.2 Contact surfaces of the two halves and the EPS content at the

interface.

Figure 9.3 PVC ring separator above the soil specimen placed in an enclosed jar.

Chapter 9

241

The specimen was placed into the container, whose screw type lid was sealed very

tightly with electrical tape for added sealing. The container was then placed in an

ice-chest and stored for a minimum of 14 days in a temperature controlled room

for attaining equilibrium. Houston et al. (1994) suggested a minimum

equilibrating period of one week. However, in the present case the specimens

were kept in the ice chest for 14 days to ensure complete equilibrium. The

temperature in the room was maintained at 22 ± 0.5o C.

After curing, the specimens were taken out of the ice chest and were immediately

weighed for the increase in moisture content of the filter paper. The most

important point of this filter paper technique is that drying and/or wetting of filter

paper from the oven-dry state can occur quickly in the laboratory environment.

Consequently, following the recommendation of Jiang et al. (2000), filter paper

weighing was performed within 30 seconds.

9.1.3 Test results and discussion

The variation of suctions with the addition of EPS beads is shown in Figures 9.4,

9.5 and 9.6 for total suction, matric suction and osmotic suction, respectively.

From the Figures 9.4 to 9.6, it can be observed that in general, the suction

increases with increasing EPS content from 0.0% to 0.9%.

SB16

SB24

SB32

0

1000

2000

3000

4000

5000

6000

7000

0 0.2 0.4 0.6 0.8 1EPS, %

Tot

al s

uctio

n, k

Pa

Figure 9.4 Variation of total suction with EPS content for three soils.

Chapter 9

242

SB16

SB24

SB32

1000

1500

2000

2500

3000

3500

0 0.2 0.4 0.6 0.8 1EPS, %

Mat

ric s

uctio

n, k

Pa

Figure 9.5 Variation of matric suction with EPS content for three soils.

SB16

SB24

SB32

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.2 0.4 0.6 0.8 1EPS, %

Osm

otic

suc

tion,

kP

a

Figure 9.6 Variation of osmotic suction with EPS content for three soils.

As discussed in Chapter 6, even though the quantity of EPS is small in terms of

mass, its volume occupies a large percentage of the soil mass. It was noticed

(Section 6.8) that the addition of 0.3%, 0.6% and 0.9% EPS occupies 7.5%,

Chapter 9

243

15.5% and 22.25% of volume in the SWEPS mixes. Hence, the addition of EPS

beads reduces the available moisture, which consequently increases the suction

potential of the SWEPS mixes.

The variation of total suction and matric suction with bentonite content reveal

different trends (Figures 9.7 and 9.8).

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

15 20 25 30 35Bentonite content, %

Tota

l suc

tion,

kP

a

Figure 9.7 Variation of total suction with bentonite content at different EPS

contents.

McKeen (1988) investigated the relationship between moisture content and soil

suction on two different clays consisting of high plasticity and low plasticity. The

results showed that at the same moisture content, higher clay content soil had a

higher suction value than that of lower clay content soil. However, in the present

case, due to the variation in moisture contents among the specimens SB32

specimens produced the lower suction values. In the present investigation, the

compacted optimum moisture content varies with bentonite content (Table 5.6). It

should be recalled that the moulding moisture content of SB16, SB24 and SB32

were 13.5%, 12.0 % and 14.0% respectively. As the optimum moisture content

and dry unit weights were different for the three soil samples tested, the variation

of suction is compared in terms of optimum moisture content and dry unit weight.

Chapter 9

244

Based on 20,000 suction tests performed on weathered clay-shale in Dallas/Fort

Worth, Reed and Kelly (1995) observed that the difference in soil suction values

are more indicative of the changes in the degree of saturation rather than in soil

moisture. On the other hand, for remoulded compacted soils, Krahn and Fredlund

(1972) and Tsai, (1993) indicated that the matric suction and total suction are

dependent on the moulding moisture content but are essentially independent of

dry unit weight.

The variations in suction with bentonite contents can also be attributed to the

hydration of bentonite with moisture. Montanez (2002) showed that an increase in

the equilibrium suction will be gained if the material is allowed to hydrate for

about 20 days prior to compaction for bentonite contents up to 15%. However, in

the present case the bentonite content was in the higher proportions (16%, 24%

and 32%). Even though for suction measurements the soil specimen was kept in

humid chamber for more than one month, SB32 specimens did not produce an

increase in suction values.

0.0% EPS

0.3% EPS

0.6% EPS

0.9% EPS

0

500

1000

1500

2000

2500

3000

3500

15 20 25 30 35Bentonite content, %

Mat

ric s

uct

ion,

kP

a

Figure 9.8 Variation of matric suction with bentonite content at different EPS

contents.

Montanez (2002) studied the influence of bentonite and sand on suction

properties. The bentonite was added in 5, 10 and 15%, to a uniform sand and also

Chapter 9

245

to a well graded sand. He observed that, in general, an increase in bentonite

content corresponds to an increase in the measured suction. In contrast to the

above, according to Chu and Mou (1981), the matric suction of compacted soils

with the same moisture content increases as the compaction energy increases.

Hence, in addition to the moisture contents, the variation in dry unit weights

might have also influenced the suction values in the present case.

The values of total suction, matric suction, peak deviator stress and the

corresponding EPS content at different confining stresses are shown in Tables 9.2,

9.3 and 9.4 for SB16, SB24 and SB32 soils, respectively.

While past studies (Mahalinga-Iyer and Williams, 1985; Reed and Kelly, 1995)

have generally suggested that an increase in soil suction is reflected in an increase

in strength, results of the current study show that the opposite is true. As discussed

in Chapter 9, this can be attributed to the compressibility of EPS beads.

Table 9.2 Relationship between suction and shear stress for SB16 (Moulding

moisture content = 13.5%).

Peak deviator stress at confining stress, kPa EPS,

%

Total Suction,

kPa

Matric Suction,

kPa 25 50 100 200 0 4101.3 1752.4 237.4 312.9 439.7 696.3

0.3 4289.4 1799.3 199.8 255.3 390.9 551.0

0.6 5277.0 2185.3 149.8 216.0 306.8 432.4

0.9 5745.7 2204.4 122.2 176.5 263.4 352.3




%

Total Suction,

kPa

Matric Suction,

kPa 25 50 100 200 0 4075.3 2139.7 304.0 373.7 460.0 679.0

0.3 4420.3 2529.5 252.1 304.2 377.9 557.3

0.6 5763.5 2909.1 212.8 222.6 298.9 488.9

0.9 4762.3 2954.6 141.9 179.4 268.2 405.0

Chapter 9

246




%

Total Suction,

kPa

Matric Suction,

kPa 25 50 100 200 0 1867.9 1393.1 303.4 337.1 429.5 581.8

0.3 1968.7 1841.6 281.2 324.8 373.6 554.1

0.6 2385.4 1985.5 237.3 267.1 315.3 468.7

0.9 3075.0 2145.5 177.0 220.7 273.1 325.0

9.2 Desiccation studies

Cracking of clay soils, a natural phenomenon that can be commonly observed in

many natural and manmade structures is due to an internal energy imbalance in

the soil mass caused by non-uniform moisture distribution, temperature

distribution, or distribution of compaction energy during construction (Fang,

1997). Cracking represents pre-failure phenomenon of a soil. Fang (1997)

classified cracks into four types, viz. shrinkage, thermal, tensile and fracture

cracks. Out of these, the most common cracking found in earth structures is

shrinkage cracking due to desiccation. This is relevant to expansive soils and

landfill covers as is described below.

When a compacted cohesive soil system is exposed to the atmosphere during hot

and dry periods, there is a reduction in soil moisture because pore water

evaporates and negative pore pressures develop in the soil. This leads to an

increase in interparticle contact forces by suction. That is, soil particles move

closer and closer reorganising into successively stable grain skeleton

arrangements. These changes increase the effective stress with consequential

reduction in volume and increase in dry unit weight. The decrease in volume

generates vertical cracks.

On the other hand, the tensile strength that provides the resistance to crack

formation increases with increased negativity of pore water pressure reflecting as

shrinkage and ultimately manifesting as desiccation cracking (Sarsby, 2000;

Mitchell and Soga, 2005). This cracking pattern produces the greatest stress

Chapter 9

247

release with the least amount of work. The cracks can be pentagonal and

heptagonal in shape, and their size appears to be uniform. The geometric shape of

the cracks depends on the clay mineral composition, the heating process, pore

fluids and other factors (Fang, 1997). The densification of the clay through

shrinkage and cracking creates an over-consolidated state.

Desiccation cracking can considerably impact the long-term performance of

compacted clayey soils in various geotechnical, agricultural and environmental

applications. For example, desiccation cracking significantly increases the

coefficient of permeability in landfill liner or covers (Kodikara et al., 2000).

Mitchell and Soga (2005) indicate that the type and amount of clay minerals

present in a drying soil control desiccation cracking. Further, the presence of

cracks changes the hydraulic properties from Darcy’s-type homogeneous flow to

fracture-dominated flow (Mitchell and Soga, 2005).

As discussed in Chapter 3, the amount and distribution of desiccation cracks,

which may or may not be distinctively visible, are probably the greatest factors in

the rate of swelling in expansive soils or landslides in slopes, dams, highway

embankments etc. The more cracks in the clay, the greater the pathways for water

to penetrate the soil, and the quicker the rate of swelling (Day, 2006).

Furthermore, this is also a major problem in compacted clay landfill liners or

covers because compacted clayey soil liners or covers are subjected to periods of

drying usually immediately after construction.

By their very nature, highly plastic clays undergo large shrinkage when dried. The

vulnerability of the clayey soils to desiccation cracking increases with increasing

compaction moisture content, increasing plasticity index, and increasing clay

content, but the dry unit weight has little effect (Kleppe and Olson, 1985; Daniel

and Wu, 1993). Boynton and Daniel (1985) observed that desiccated clays

undergo some self-healing upon wetting. However, the degree to which cracks

close is very sensitive to the applied overburden stress. They also found that

cracks can penetrate several inches into compacted clay in less than 24 hours. In

addition, it was also observed that severe desiccation can extend to depths of up to

1m, and probably deeper (Koerner and Daniel, 1997). Over longer periods, the

Chapter 9

248

problem of protecting underlying soils from desiccation would be even more

difficult because the probability of an extreme weather event occurring increases

with the passage of time.

Presently to provide protection against desiccation in landfill covers, a

geomembrane in the underlying barrier layer combined with adequate cover soil is

the best way (Koerner and Daniel, 1997). However, based on field monitoring of

test covers and cover failures Koerner and Daniel (1997) mentioned that even

though a compacted clay layer is protected with geomembrane, there are still

cases in which thermally induced flow could eventually desiccate even a

geomembrane-covered compacted clay barrier layer. Thus there is a need to do

further research to find other alternative materials to control desiccation cracking.

A photograph of desiccation crack in field compacted clay covers is shown in

Figure 9.9

Basnett and Brungard (1992) observed desiccation cracks on the side slopes of

clay liner during landfill construction. The cracks were 13- 25 mm in width and

extended to a depth of 0.30 m.

Milller and Mishra (1989) observed desiccation cracks during their field

investigation of landfill liners. The cracks exceeded 10 mm in width and some

penetrated the entyre depth (0.30 m) of the compacted clay layer.

Montgomery and Parsons (1989) observed desiccation cracking at test plots

simulating covers constructed at a landfill in Wisconsin. Subsequent to 3 years of

exposure, the upper 0.20 – 0.25 m of the compacted clay plots has become

desiccated, with crack widths exceeding 13 mm. Maximum cracks depths of 1.0

m were reported at a number of locations in the test plots.

Chapter 9

249

Figure 9.9 Example of desiccation cracking in compacted clay in field

(adapted from Daniel and Wu, 1993).

9.2.1 Variation of desiccation tests

From literature survey it was observed that there is no single method used to

obtain the desiccation cracking of soil samples. It varied in different sample sizes,

different conditions of moisture content and different thicknesses of samples. The

following review briefly presents the methods adopted by various researchers.

Corte and Higashi (1960) (cited in Kodikara et al., 2000) have conducted

remarkable sets of experiments to understand the free shrinkage by using flat

wooden containers of 600 mm x 840 mm plan area and 70 mm depth. The soil

used was in two initial states: slurry and loosely compacted soil. Room

temperature was 22oC and relative humidity was 30 to 40%. In addition, various

base materials like plain wood, greased wood, sheet of glass and 20 mm thick

layer of sand were used to observe the adhesion of the soil to the bottom material

of the container. They observed that the desiccation crack pattern is more

dependent on the thickness of the soil layers than on temperature of air humidity.

Further, shrinkage also depends on the material at the bottom of the container.

Kleppe and Olson (1985) determined the severity of cracking by preparing flat

plates of the sand-clay mixtures. They observed that increases in the moisture

content of similar compacted soils increased the desiccation cracking.

Chapter 9

250

Lau (1987) (cited in Kodikara et al, 2000) conducted cracking tests on a flat

wooden container of 610 mm × 610 mm plan area and 76 mm deep. The soils

were prepared at their liquid limit and the soil was close to a slurry state. The soil

was instrumented with four embedded ceramic-cup tensiometers to measure the

soil suction during the tests.

Fang (1997) described the method developed at Lehigh University for cracking

pattern test. In this method, all soil samples must be passed through a #40 U.S.

standard sieve. Approximately 50 to 100 g of soil are needed to perform the test.

Moisture content of the specimens must be at the full saturated condition.

Generally at the liquid limit. Then the paste is spread uniformly on a clean glass

plate to a thickness of approximately 1.3 mm (1/20"). The drying process can be

determined from three common methods like room temperature, oven drying or

microwave oven drying methods.

Zeigler et al. (1998) studied the cracking pattern using a 100 mm diameter and

116 mm high cylindrical standard Proctor mould specimens. Cracks were

observed for each specimen that was subjected to a different number of

drying/wetting cycles. The drying cycle consisted of placing the specimen in an

oven at 48o C for a period of 24 hours. For each wet cycle, the specimen,

contained in the mould, was submerged in distilled water at room temperature for

a period of 24 hours. The amount of surface cracking that occurred in the

specimen was quantified by measuring the width and approximate length of

cracks along the cylindrical face of a quadrant of the specimen. Then the total area

of crack was calculated by multiplying with 4. The soil was compacted at a

moisture content 3.5% above optimum moisture content.

Colina and Roux (2000) studied the cracks in a clay-sand mixture with 160 mm ×

160 mm surface area with varying thicknesses of 16 mm, 10 mm, 4 mm and 2

mm. The soil sample was in a slurry state.

Yesiller et al. (2000) conducted experiments using a steel reinforced plexiglass

tank. Dimensions of the tank are 1.0 m length, 1.5 m width and 0.5 m depth. It

was fitted with a rainfall simulator system, a drying system and surface crack

Chapter 9

251

recording system. A rainfall nozzle and fans were used for cyclic wetting and

drying of the soils. To describe the extent of surficial cracking, crack intensity

factor (CIF) was introduced as a descriptor. CIF was determined by using

scanned photographs of soil surfaces and analysed using MATLAB®. The soil

was compacted at a moisture content ±2% at optimum moisture content. They

observed that fines content in soils affected the cracking behaviour significantly

and the extent of cracking was not correlated directly to the plasticity index of the

soil used in the study. Further, they noticed that cracking subsequent to wetting

was greater than cracking subsequent to compaction. That is the extent of

cracking is a function of both the amount of water in the soil at the onset of drying

and suction attained during drying.

Albrecht and Benson (2001) observed cracking behaviour from cylindrical

specimens compacted in a compaction mould and subjected to wetting and drying

cycles. The cracking pattern was observed at the end of three drying cycles.

Tay et al. (2001) observed desiccation cracking using 800 × 800 mm2 beds of

compacted sand-bentonite mixtures. The dimensions of the wooden box are 800

mm × 800 mm × 250 mm. They were compacted using a handheld vibrating

pneumatic hammer (a Kango 638 light demolition hammer) with 80 mm × 100

mm rectangular plate. Further, small samples were also tested by using 200 mm ×

200 mm × 200 mm boxes. The soil sample was compacted at optimum moisture

content. Hot air at 30o C was supplied.

Kodikara et al. (2002) used a split cylindrical mould of 100 mm diameter by

varying specimen thickness to 20 mm and 40 mm for desiccation tests. Super

strength Araldite, an epoxy resin glue was added inside the mould to apply zero

lateral strain boundary condition. They showed that specimen thickness can

influence the characteristics of the cracks that develop. Further, Kodikara et al.

(2000) stated that the shrinkage cracks characteristics are governed by the

thickness to diameter ratio. In addition, they stated that soil density will also

influence the crack pattern. That is, they noticed hexagonal crack patterns were

more common in loose packed soils than soil slurry. The soil was saturated to

achieve equilibrium with pore liquid pressure.

Chapter 9

252

Miller and Rifai (2004) used soil samples of 457.2 mm diameter and 101.6 mm

high steel moulds for determination of crack characteristics. The samples were

compacted at 2% wet of optimum moisture content. Geometric features of the

cracks were monitored at the end of each drying cycle using digital images of the

clay surface.

Vogel et al. (2005) prepared sand (S) and bentonite(B) mixtures in the ratio of 1:1

and 5:1 refereed as SB1:1 and SB5:1 respectively to study the crack dynamics in

clay soil. Sand and bentonite were mixed with water using a mixer to get a paste

with optimal consistency. Then the mixtures were distributed on glass plates of

240mm × 300mm. The clay layer had a constant thickness of 5 mm. The surface

was uniformly illuminated with oblique incident light form four halogen lamps

and a digital camera was installed to record the surface during desiccation at fixed

time intervals.

This review demonstrates that there is a need to investigate the factors that

influence the cracking of soils in controlled test specimens. That is, how the

diameter of specimen influence cracking, how the variation in depths for a same

diameter specimen influences the cracking, needs to be investigated.

9.2.2 Sample preparation

In the present investigation, the specimens were prepared based on the Lehigh

method described by Fang (1997). The specimen moisture content was similar to

volumetric shrinkage specimens. However, there was variation in the thickness of

specimens prepared. According to the Lehigh method, smaller particle sizes or

larger surface area per unit volume of soil specimen would give more distinct

cracking pattern. Hence, soil paste to a thickness of 1.27 mm (1/20") was

prescribed for observing cracking behaviour of soils. As recycled EPS beads of 3-

9.5 mm in diameter were added to the soil, it was decided to use a minimum

thickness of 20 mm for all SB and SWEPS specimens.

For the desiccation studies, as was done for the volumetric shrinkage tests, the

moisture content of the SB mixes was prepared at the liquid limit by saturating

Chapter 9

253

with distilled water in a slurry state. EPS beads in required quantities were mixed

to the soil slurry. Subsequently, the mixed slurry, free of air bubbles, was poured

into PVC ring moulds pre-cut to the required diameters and heights as given in

Table 9.5. The moulds were placed on a glass plate, which was lightly smeared

with silicone grease to minimise friction before pouring the mixed slurry. The soil

samples were slowly tamped with a plastic rod of 5 mm diameter. After tamping,

the top surface of each specimen was levelled with a straightedge.

Colina and Roux (2000) stated that in sand-clay mixes, the sand granulometry in

the composite was adequate to avoid significant sedimentation in the mould. In

addition, the thixotropy of the clay was helpful to prevent or minimise

sedimentation. In the present study, as the reconstituted soil samples are made

from sand and bentonite, sedimentation was assumed to be minimised.

All the test specimens were subjected to drying after slurry placement. The drying

process was carried out through air dry process under atmospheric conditions

(temperatures of 22 ± 2°C, relative humidity approximately 60%) until the crack

and shrinkage seemed to be consistent and no further changes were observed.

Cracking was more severe for specimens prepared at slurry state than at moist

state. As described in the studies on volumetric shrinkage of SB mixes (refer to

Section 8.5), at slurry state the moisture content of the clayey particles is high

which can produce more desiccation. At optimum moisture content (OMC), SB

mixes showed no distinct pattern of desiccation cracking even at 32% bentonite

content. Hence, to study their cracking characteristics and for comparison

purposes, the soil specimens were prepared and compacted in a slurry state or

liquid limit state.

Kodikara et al. (2002) suggested that soil restraint was an important factor for the

test and applied glue between the soil and ring to maintain zero lateral strain

conditions at this location. The same was tried in the current research. However,

owing to the slurry state of the soil sample, a proper bond between the wet soil

sample and the ring could not be achieved. Hence, glue was not applied at the

interface between the mould and the soil sample in the current research.

Chapter 9

254

9.2.3 Variables investigated

The tests were carried out on three soil types with four EPS contents, two ring

diameters and five ring heights. Table 9.5 shows the parameters and variables in

the testing program.

Table 9.5 Variables in desiccation studies.

Parameters Variables

Soil SB16, SB24 and SB32

EPS contents 0.0%, 0.3%, 0.6% and 0.9%

Diameters 150 mm and 86 mm

Heights 70 mm, 35 mm and 20 mm (for 150 mm diameter samples)

40 mm and 20 mm (for 86 mm diameter samples)

H/D ratios 0.47 (70 mm/150 mm and 40 mm/86 mm)

0.23 (35 mm/150 mm and 20 mm/86 mm)

The rationale behind this testing program was to observe the effect of EPS

inclusion by considering two aspects. The first aspect was to keep height/diameter

(H/D) ratio of the specimen constant and the second was to keep the height of the

specimen constant but vary the diameters. Figure 9.10 shows the set up of test

specimens.

9.2.4 Surficial crack quantification

Surficial cracks can usually be quantified by comparing the area of cracks with the

total surface area of soil specimen tested. The techniques for this purpose, which

range from manual measurements to computer aided image analysis programs,

can be adopted to evaluate the crack intensities. In a manual method, the area of a

crack is defined as the product of its length and width. In a computer aided image

analysis, however, the crack area is determined by analysing the pixel area

between contrasting colours from a photograph. Al-Wahab and El-Kedrah (1995)

quantified the cracks through manual measurements whereas Miller et al. (1998)

and Yesiller et al. (2000) used a computer image analysis program.

Chapter 9

255

Figure 9.10 Desiccation specimens under observation.

Miller et al. (1998) and Yesiller et al. (2000) have introduced Crack Intensity

Factor (CIF) as a descriptor in quantifying the extent of surficial cracking in a soil

mass, which is defined as below.

t

c

AA

CIF = (9.1)

Where Ac is the area of cracks and

At is the total surface area of the drying soil mass where the crack is

observed

In a computer aided image analysis program, the surficial cracking area can be

determined using scanned photographs of the desiccating soils. In this way the

cracks can appear darker than remaining uncracked soil surface. The contrast

between the colour of the cracks and uncracked soil is used to calculate the CIF.

In the current study, scanned photographs of soil surfaces were analysed using

MATLAB® to determine CIF.

MATLAB® consists of various tools for technical computation such as Data

Analysis and Exploration, Mathematical Algorithms, Modelling and Simulation,

Visualization and Image Processing. In Visualization and Image Processing,

MATLAB® provides immediate access to graphics features that allow the user to

visually understand the data. MATLAB® reads, writes and displays byte and

floating-point image data. It has capability of image transforms and image

Chapter 9

256

analysis. Hence, this software was selected for the analysis of cracks based on the

digital photographs.

9.2.5 Image acquisition setup

To use in the computer aided image analysis program, the surface area of the

crack from drying soil mass was extracted from digital photographs. The general

view of the image acquisition set up for taking the digital photos is shown in

Figure 9.11. To minimise the variabilities that would have arisen due to manual

handling, the digital camera was mounted on tripod. The position of the camera

was adjusted in such a way that (i) the test specimen was always centred and (ii)

the background plane was perpendicular with respect to the axis of camera lens. In

order to obtain a better contrast between the specimens and the background pixels,

a black plastic pad as shown in Figure 9.11 was placed as background. To

maintain the correct alignment, each specimen was accurately positioned between

white colour markings pre-drawn on the black plastic pad.

Figure 9.11 Extraction of surface cracking from specimens.

Chapter 9

257

(a) (b)

Figure 9.12 (a) Photograph of the SWEPS mix and (b) Inverted image of the photograph in black and white.

The photographs were taken with an Olympus D-540 camera with 3X optical

zoom which can capture 3.2 mega pixels. In addition to fluorescent lightings and

natural light, flashlight of the camera was also utilised during the image

acquisition. The test specimens were placed on exact markers. With the height of

the camera and other parameters including lighting being the same, a minimum of

three photos were taken for each specimen for analysis. Due to the long duration

of the test, shutting down and reactivation of the camera were unavoidable. In

such cases, the camera position would have changed slightly due to touching.

Therefore, as suggested by Oren et al. (2006), the specimen was always

positioned in between the markings each time prior to imaging, to control the

distortion.

By using MATLAB® version 7 image processing software, the surface crack area

was determined for soils with and without EPS inclusion. In this work, the

segmentation algorithm applied was based on the difference of the intensity level

of the pixels. For that purpose, the true colour images (Figure 9.12 (a)) were

converted into black and white images (Figure 9.12 (b)). From the latter, the

number of black pixels was measured. This number is divided with total number

of pixels from the total soil specimen to obtain the CIF value.

Chapter 9

258

9.2.6 Test results and discussion

9.2.6.1 Effect of EPS on desiccation of soil

The variation in the CIF with EPS content for SB16, SB24 and SB32 at different

specimen heights for 86 mm diameter and 150 mm diameter soil specimens are

shown in Figures 9.13 and 9.14, respectively. From these figures it can be

observed that in all cases, irrespective of the height of the specimen, CIF followed

a decreasing trend with increasing EPS content for the three soils.

The potential for shrinkage cracking should be viewed as likelihood for exceeding

material failure tensile strain by the shrinkage strain (Chakrabarti and Kodikara,

2007; Kodikara, 2006). Since shrinkage strain reduces with increasing EPS

content, this is an advantage. At the same time, based on triaxial data, it appears

that failure tensile strain is also increasing (material becomes more flexible). This

is also an advantage in reducing the shrinkage cracking potential.

86 mm dia, 20 mm high

SB16

SB24

SB32

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(a)


SB16

SB24

SB32

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(b)

Figure 9.13 Variation of CIF with EPS for 86 mm diameter specimens at varying

heights of (a) 20 mm and (b) 40 mm.

Chapter 9

259


SB16

SB24

SB32

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(a)

150mm dia, 35 mm high

SB32

SB16

SB24

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(b)


SB16

SB24

SB32

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(c) Figure 9.14 Variation of CIF with EPS for 150 mm diameter specimens at varying

heights of (a) 20 mm, (b) 35 mm and (c) 70 mm. .

Chapter 9

260

In addition, from the Figures 9.13 and 9.14, it is immediately obvious that the

addition of recycled EPS has a significant effect on the CIF values. The CIF

decreases linearly with the addition of recycled EPS beads for all three soils

across all specimen heights.

9.2.6.2 Influence of bentonite content on CIF

Another notable observation from Figures 9.13 and 9.14 is that the higher

bentonite content of the soil, the higher the CIF for that soil. That is SB32

exhibited higher CIF, followed by SB24, and next by SB16. This means that the

fine fraction of the soil has a significant effect on the crack pattern of the soils.

According to Mitchell and Soga (2005) and Fang (1998), the higher the clay

fraction in a soil, the higher the cracking potential of that soil. For the SWEPS

specimens, the results of the current study are also in agreement with this

observation. Due to its higher bentonite content and the relatively higher liquid

limit when compared with other soils, SB32, for example, shows a high CIF

value. This behaviour is consistent with other soils and in agreement with Yesiller

et al. (2000).

9.2.6.3 Influence of height of specimen on CIF

Until now, the experimental work required to obtain CIF values has not been

standardised. Research in the past (Corte and Higashi, 1960; Lau, 1987; Fang

1987; Zeigler et al., 1998; Colina and Roux, 2000; Yesiller et al. 2000) has

employed various specimen sizes and H/D ratios. Hence, it was considered

prudent in the current study to investigate whether CIF values are significantly

affected by specimen dimensions.

Figure 9.15 shows the variation of CIF with EPS content for 150mm diameter

specimens with different heights for each soil-bentonite mix. It is seen that despite

the data scattering, the CIF values vary with respect to height of the specimen.

The variations are in the range of 5 to 30%.

Chapter 9

261

SB16, 150 mm dia

45

67

89

1011

12

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

20 mm high35 mm high70 mm high

(a)

SB24, 150 mm dia

9

10

11

12

13

14

15

16

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %


(b)

SB32, 150 mm dia

11

13

15

17

19

21

23

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %


(c)

Figure 9.15 Variation of CIF with EPS content for 150 mm diameter specimens at varying heights for (a) SB16, (b) SB24 and (c) SB32.

Chapter 9

262

SB16, 86mm dia

0

2

4

6

8

10

12

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

40 mm high

20 mm high

(a)

SB24, 86 mm dia

0

3

6

9

12

15

18

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

20 mm high

40 mm high

(b)

SB32, 86 mm dia

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

20 mm high

40 mm high

(c)

Figure 9.16 Variation of CIF with EPS content for 86 mm diameter specimens at varying heights for (a) SB16, (b) SB24 and (c) SB32.

Chapter 9

263

To investigate whether the similar behaviour is evident in smaller diameter soil

specimens, additional tests were conducted using 86 mm diameter specimen sizes.

Figure 9.16 shows the variations of CIF with specimen height and EPS content for

86 mm diameter specimens. Similar to those of 150 mm specimens, these results

show that specimen height has some effect on the CIF value.

9.2.6.4 Influence of H/D ratio on CIF

According to Kodikara et al. (1999), the desiccation behaviour of soil in the

laboratory is influenced by H/D ratio of the test specimen. To investigate if this

observation is valid for the current study, two H/D ratios were considered i.e. 0.47

and 0.23.

For H/D ratio of 0.47, two specimen sizes were considered: 150 mm diameter by

70 mm high specimens, and 86 mm diameter by 40 mm high specimens. For H/D

ratio of 0.23, two specimen sizes were considered: 150 mm diameter by 35 mm

high and 86 mm diameter by 20 mm high specimens. The variations of CIF in

both cases, for three soil types of SB16, SB24 and SB32 is presented in Figures

9.17 and 9.18. In all the cases the trend is consistent and the difference is only

marginal.

Figures 9.17 and 9.18 indicate that irrespective of soil type, if the ratio of H/D is

maintained constant, specimen diameter is not going to significantly affect the test

results. Hence, in comparing the cracking behaviour of different soils, smaller

size specimens may be chosen for practical reasons.

Chapter 9

264

SB16, H/D = 0.47



4

5

6

7

8

9

10

11

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(a)

SB24, H/D = 0.47



8

10

12

14

16

18

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(b)

SB32, H/D = 0.47



10

12

14

16

18

20

22

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(c)

Figure 9.17 Variation of CIF with EPS for H/D of 0.47 for (a) SB16, (b) SB24 and (c)

SB32.

Chapter 9

265

SB16, H/D = 0.23150 mm dia, 35 mm high


0

2

4

6

8

10

12

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(a)



0

3

6

9

12

15

18

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(b)



0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(c)

Figure 9.18 Variation of CIF with EPS for H/D of 0.23 for (a) SB16, (b) SB24 and (c) SB32.

Chapter 9

266

9.2.6.5 Influence of H/D ratio and soil type on CIF

Variation of CIF with H/D ratio is presented in Figure 9.19. From the figure it can

be observed that for any particular soil type the variation in H/D ratio has not

produced significant variation in CIF values.

SB16

H/D = 0.47 H/D = 0.23

0

2

4

6

8

10

12

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(a)

SB24H/D = 0.47

H/D = 0.23

0

3

6

9

12

15

18

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(b)

SB32

H/D = 0.47

H/D = 0.23

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1EPS, %

CIF

, %

(c)

Figure 9.19 Variation of CIF with EPS content for H/D of 0.47 and 0.23 for (a) SB16,

(b) SB24 and (c) SB32.

Chapter 9

267

Kodikara et al. (2000) stated that the characteristics of desiccation shrinkage

cracks that develop in a soil masses are influenced by the height to diameter ratio.

Kodikara et al. (2002) also noted that the crack widths in thinner specimens (20

mm height) were greater than those in thicker specimens (40 mm height). Based

on these they argued that specimen thickness may influence the desiccation test

results.

The observations of Kodikara et al. (2002) are confirmed by the results of the

current study. Thinner specimens exhibited greater crack width than thicker ones.

However, when analysed based on the CIF, the resulting difference in their

surficial cracks, as shown in Figure 9.18, is not significant.

9.3 Relationship between volumetric shrinkage and CIF

It is known that volumetric shrinkage is an important indicator of the desiccation

crack potential in soils. To understand the relationship between the volumetric

shrinkage and CIF, a graph was drawn between these parameters as shown in

Figure 9.20.

0

5

10

15

20

25

30

35

0 5 10 15 20 25CIF, %

Vo

lum

etric

shr

inka

ge, %

SB16SB24SB32

Figure 9.20 Variation of volumetric shrinkage with CIF.

Chapter 9

268

From the Figure 9.20 it can be observed that SWEPS mixes have relatively

isotropic shrinkage as given by the following equation

Isotropic volumetric shrinkage = ( ) 23

11 CIF−− (9.2)

Where CIF is the Crack Intensity Factor, %

9.3 Summary

The suction and desiccation behaviour of SWEPS mixes is described in this

chapter. The suction was carried out using the filter paper method. It was

observed that with the addition of EPS beads, the suction in the soil increases.

This could be attributed to the reduced moisture availability with increased EPS

volume in SWEPS mixes. In addition, the variation could also be due to the

differences in the dry unit weights and optimum moisture contents of SB and

SWEPS mixes. However, the increased suction is not expected to increase the

compressive strength of the SWEPS mixes.

The desiccation characteristics of SB and SWEPS mixes were studied at slurry

state corresponding to the liquid limit. The rationale behind this testing program

was to observe the effect of EPS inclusion by considering two aspects. The first

aspect was to keep height/diameter (H/D) ratio of the specimen constant and the

second was to keep the height of the specimen constant but vary the diameters.

The desiccation characteristics were analysed from Crack Intensity Factor (CIF)

using MATLAB®. It was found that the H/D ratio does not influence the CIF

significantly. It was observed that addition of EPS beads reduces the crack

intensities in expansive soils. However, this reduction depends on the expansive

clay fraction in soils.

In the present case, the addition of recycled EPS beads is akin to the addition of

coarse grained soils to clays. The factors contributing to the reduced cracks in the

soils can be due to reduced unit weight, reduced clay fraction and reduced surface

area of the clay particles with the addition of EPS beads.

269

CHAPTER 10 - HYDRAULIC CONDUCTIVITY, COMPRESSIBILITY AND

WATER BALANCE ANALYSIS OF A SWEPS MIX

One of the possible applications considered for SWEPS mixes was landfill cover

due to its ability to control desiccation cracking. This chapter describes the

hydraulic conductivity, compressibility and water balance analysis carried out on

a soil-EPS mix for one of the reconstituted expansive soils (SB24). Only limited

investigations were carried out due to time limitations. Water balance analysis

was carried out using HELP simulation model on SB24 soil with and without EPS

beads. This particular soil was selected because it is in the medium plasticity

range. The EPS content investigated was 0.0%, 0.3% and 0.6%.

10.1 Hydraulic conductivity

The principal factor affecting the performance of any landfill cover system is their

hydraulic conductivity. Hydraulic conductivity is defined as the rate of water flow

under laminar flow conditions through a unit cross sectional area of porous

medium under unit hydraulic gradient and standard temperature conditions.

Typically, hydraulic conductivity value must be less than or equal to 1x10-9 m/s

for soil liners and covers used to contain hazardous, industrial and municipal

wastes (Daniel and Benson, 1990). The hydraulic conductivity of compacted clay

soils is influenced by soil composition and compaction variables (Osinubi and

Nwaiwu, 2006).

Due to the time constraints, tests were only conducted to investigate the effect of

recycled EPS beads inclusion (0.0%, 0.3% and 0.6%) on the hydraulic

conductivity of a sand-bentonite mix (SB24).


Hydraulic conductivity test can be conducted using different types of

permeameters such as rigid-wall permeameter, flexible wall permeameter and

consolidation cell. A review of the advantages and disadvantages of the apparatus

was described by Kamon and Katsumi (2001).

Chapter 10

270

In the present research, all the hydraulic conductivity tests were conducted in the

rigid-wall compaction mould permeameters using the falling head method in

accordance with Head (1994) and AS 1289.6.7.2 (2001). The rigid wall

permeameter used in the current research was a compaction mould made of

corrosion resistant tube with top and bottom plates. The diameter of the

permeameter was 100 mm. No overburden pressure was applied to the test

specimens, similar to the tests carried out by Daniel and Wu (1993);

Chalermyanont and Arrykul (2005) and Osinubi and Nwaiwu (2006).

Using the equipment described above, the vertical pressure on specimen’s ends

cannot be controlled. While the choice of test method has been dictated by

equipment availability and test practicality, it is realised that it may not represent

other swelling conditions where specific overburden pressure exists. Byonton and

Daniel (1985), for example, found that under overburden pressure, the cracks

developed in clay layers tend to close. With the above equipment, end pressure

can still develop because of the restrained swelling, but its quantification is

difficult.

According to Kodikara (2001), rigid wall permeameters are particularly suitable

to testing very low permeable and relatively stiff materials such as stabilised soils

and concrete. As an additional advantage, this method can be conducted directly

on as-compacted or as-sampled specimens. In spite of the possibility of side wall

leakage, this permeameter is still being used by many researchers. In testing

bentonite mixes, Imamura et al. (1996) found that side wall leakage is not of a

concern even when hydraulic gradient is applied because of the swelling nature of

bentonite. Furthermore, according to Daniel and Wu (1993), this type of test can

yield results comparable to those obtained from flexible-wall permeameters (i.e.

triaxial) with back pressure application. It should be noted however, that triaxial

testing apparatus has certain drawbacks. For example, the stepwise application of

the back pressure and the cell pressure in triaxial apparatus have to be done with

great care to avoid pre-consolidation which leads to unrealistically low value of

hydraulic conductivity which may influence the design (Gartung and Zanzinger,

1998).

Chapter 10

271

The permeant fluid used was de-aired tap water. To ensure the accuracy of the test

results and to determine if a test can be terminated, AS1289.6.7.2 (2001)

recommends running the test until the differences in the measured hydraulic

conductivity over at least a 24 h period do not exceed 20% of the lowest measured

hydraulic conductivity in that period. It also suggests that the average readings be

reported. These criteria were followed in the present case. The specimen was

saturated before the test by removing the entrapped air using a suction pump and

air tight chamber.

10.1.2 Effect of EPS on hydraulic conductivity of soil

The variation of hydraulic conductivity of SB24 with the addition of EPS at their

respective maximum dry unit weight and optimum moisture content is shown in

Figure 10.1. The hydraulic conductivity of the SB24 soil without EPS beads is

1.18 × 10-9 m/s. This is increased to 2.36 × 10-9 m/s and 1.25 × 10-8 m/s with the

addition of 0.3% and 0.6% EPS beads respectively to the SB24 soil.

It is seen that the hydraulic conductivity of the soil-EPS mixes increases slightly

with 0.3% EPS when compared with the control soil, but with 0.6% EPS a

moderate increase (one order of magnitude) is observed. As previously

mentioned, it is generally accepted that hydraulic conductivity for a landfill liner

or cover materials should be around 10-9 m/s or less. While the control soil and

soil with 0.3% EPS content may satisfy this criterion, soil with 0.6% EPS content

may only be used as a cover material e.g. evapotranspiration cover.

For a mix of 24% bentonite and uniform fine sand, Kenny et al. (1992) reported

hydraulic conductivity in the range of 10-9 to 10-10 m/sec for a range of moisture

contents from 17% to 22%. Similarly, Komine and Ogata (1996) noticed

hydraulic conductivity readings in the same range for 20% to 30% bentonite

contents. The hydraulic conductivity of SB24 mix without EPS from the present

research (1.1 × 10-9 m/sec) is in agreement with the above results.

In a comprehensive experimental study, Rodatz and Oltmanns (1997) carried out

testing to understand the hydraulic conductivity characteristics of fibre-reinforced

soils for landfill liner systems. Three types of soils referred as clay, loam and sand

Chapter 10

272

were compacted to their maximum Proctor dry density and tested for the hydraulic

conductivity using triaxial cells. They noticed that for clay specimens, the

hydraulic conductivity remained unchanged (k = 3.0 × 10-11 m/sec) for most

specimens, up to a 1.0% fibre content. However, hydraulic conductivity increased

considerably at fibre contents above 1.5 or 2.0% (presumably due the connected

drainage paths on the surface of fibres). Interestingly, they observed that short

fibres (similar to the EPS granules in the present study) failed to produce any

marked increase in hydraulic conductivity up to a fibre content of 3%.

SB24

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7EPS, %

Hyd

raul

ic c

ondu

ctiv

ity, m

/s

Figure 10.1 Variation of hydraulic conductivity with EPS.

In line with the findings from the present study, Al-Tabbaa and Aravinthan (1998)

observed an increase in hydraulic conductivity with the addition of tyre chips to a

natural clay to be used as a landfill barrier material. With the addition of tyre

chips, they obtained hydraulic conductivity values of 3.8x10-9, 5.1x10-9 and 7.7 ×

10-9 m/sec for clay, clay-tyre (8%, 1-4 mm) and clay-tyre (15%, 4-8 mm),

respectively. They concluded that the increase in hydraulic conductivity was not

significant due to a good bonding between the clay and tyre chips. They also

noticed that the development of large pores and cracks was minimal.

Chapter 10

273

Similarly, Miller and Rifai (2004) carried out hydraulic conductivity testing on

fibre-reinforced clayey soil in a desiccation study that has been described in

Chapter 3. They observed that the hydraulic conductivity generally depends on the

fibre content. The general trend was with an increase in fibre content there was an

increase in hydraulic conductivity value. Furthermore, they noticed that at fibre

contents of greater than 1% the increase was more pronounced. However, the

addition of 0.4% to 0.5% of fibre content to soils maintained the hydraulic

conductivity below 1 × 10-9 m/sec.

The three references above demonstrate that the addition of fibres or tire chips did

not alter the hydraulic conductivity within a certain limit. The same trend was

confirmed in the present study; up to 0.3% of EPS content, the hydraulic

conductivity of the SWEPS was within the acceptable limits (10-9 m/s) for a

landfill cover material (see also next section).

10.2 Compressibility characteristics

In addition to the hydraulic conductivity characteristics the compressibility

characteristics of SWEPS mixes were also investigated. This allowed the

influence of EPS beads on the compressibility of the soil to be understood. In

addition, this test also provides an indirect determination of the hydraulic

conductivity.


The test procedure was performed according to AS 1289.6.6.1-1998. Each soil

sample, with or without EPS beads, was statically compacted at the MDD-OMC

state in an oedometer ring of 76 mm diameter and 19 mm height. The compacted

specimen was saturated prior to consolidation test by water submersion while

restraining the vertical swelling by loading increments. Table 10.1 shows the

swell pressure at which saturation was achieved.

Chapter 10

274

Table 10.1 Initial pressure and subsequent pressure increments.

EPS Swell pressure

(kPa)

Subsequent pressure

increments (kPa) 0.0% 100 200

400 800

0.3% 80 100

200 400

0.6% 53 100

200 400

10.2.2 Test results

The nature of the rate of consolidation can be evaluated from the coefficient of

consolidation, cv. In the present case cv was determined from the log-time method

also known as Casagrande method. In addition, the coefficient of volume

compressibility, mv, was also determined. From these two values, the hydraulic

conductivity was also back calculated using the following equation.

wvvmck γ= (10.1)

In the equation, vc is the coefficient of consolidation;

vm is the coefficient of volume compressibility and

wγ is the unit weight of water.

Typical log time plot corresponding to the first increment from which the

coefficient of consolidation was obtained for SB 24 with 0.0%, 0.3% and 0.6% is

shown in Figure 10.2 (a), (b) and (c) respectively.

Chapter 10

275

0.0% EPS

200

300

400

500

600

0.1 1 10 100 1000 10000 100000Time, min

Dia

l gau

ge r

eadi

ng, d

iv

(a)

0.3% EPS

300

400

500

600

700

0.1 1 10 100 1000 10000 100000Time, min

Dia

l gau

ge r

eadi

ng, d

iv

(b)

0.6% EPS

-100

0

100

200

300

400

500

0.1 1 10 100 1000 10000 100000Time, min

Dia

l gau

ge r

eadi

ng, d

iv

(c) Figure 10.2 Typical log-time plot for the first increment of loading (a) 0.0% EPS,

(b) 0.3% EPS and (c) 0.6% EPS

Chapter 10

276

A typical time vs. decrease in height of the consolidation specimen at the initial

increment in pressure is shown in Figure 10.3. It can be observed that the addition

of EPS beads made the specimen more compressible. This may be mostly

attributed to the compressibility of EPS beads, rather than the decrease in voids of

the SWEPS specimen.

SB24

0.0% EPS (200 kPa)

0.3% EPS (100 kPa)

0.6% EPS(100 kPa)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0.1 1 10 100 1000 10000 100000Time, min

% d

ecre

ase

in h

eigh

t

Figure 10.3 Percent decrease in height with time at initial consolidation pressure.

The variation of coefficient of volume compressibility and coefficient of

consolidation are shown in Figures 10.4 and 10.5 respectively. It can be seen that

the coefficient of volume of compressibility increases with increasing EPS

content. Similar is the case with the coefficient of consolidation. The coefficient

of consolidation increases steeply with the addition of EPS beads due to the

compression of EPS beads. It should be noted that EPS is compressible in nature.

Hence during the consolidation process, in addition to soil, EPS beads also

undergo compression. This analysis gives an approximate indication of how

SWEPS mixes behave in consolidation process. Similar to the present

observation, with the addition of fibres to fly ash, high compressibility was noted

in the fly ash – fibre mix by Kaniraj and Gayathri (2003).

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277

SB24

0

0.0001

0.0002

0.0003

0.0004

0.0005

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7EPS, %

mv,

kP

a-1

Figure 10.4 Variation of mv with EPS content.

SB24 0.3% EPS

0.6% EPS

0.0% EPS

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 100 200 300 400 500 600 700 800 900Vertical effective stress, kPa

c v, m

2 /sec

Figure 10.5 Variation of cv with vertical effective stress at different EPS contents.

Chapter 10

278

SB24

Permeameter

Consolidation (200 kPa)

Consolidation (400 kPa)

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

EPS, %

Hyd

raul

ic c

ondu

ctiv

ity, m

/sec

Figure 10.6 Variation of hydraulic conductivity with EPS content.

The variation of hydraulic conductivity with the addition of EPS beads to

reconstituted soil (SB24) is shown in Figure 10.6. It can be observed from Figure

10.6 that, based on the results of the consolidation tests, the addition of EPS beads

of up to about 0.3 - 0.4% increases the hydraulic conductivity. However,

additional EPS does not significantly produce a further increase in the hydraulic

conductivity of SWEPS. In addition, it can also be observed that to lower the

hydraulic conductivity, consolidation of the SWEPS mix can be performed.

Overburden pressure is thus an important factor needed in reducing the hydraulic

conductivity of SWEPS mixes.

In general, 400kPa should produce a lower value of k than 200 kPa effective

overburden pressure. However, there are instances in the literature (Porbaha et al,

2000; Kaniraj and Gayathri, 2004) that there is a large variation between the

measured values of k from the permeability tests and back-calculated values form

the consolidation tests. This discrepancy was attributed to the errors in the

determination of cv from the conventional methods. They both concluded that the

permeability should be measured directly rather than back-calculated values.

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279

10.3 Water balance analysis using Visual HELP software

Since the addition of EPS to the soil has been observed to be useful in controlling

the desiccation cracking (Chapter 9) and the hydraulic conductivity of SWEPS is

not appreciably different from that of soil without EPS beads (Section 10.1), one

may say that SWEPS may find a useful application as a landfill cover material.

With its lightweight, ductile characteristics and ability to offer considerable cost

saving, SWEPS mixes may also be used in other barrier applications where direct

contact with hydrocarbons can be avoided. In the current study, the potential of

SWEPS as a cover material is further explored.

In any closed landfill, the most significant factor contributing to leachate

generation is percolation of water through the landfill final cover (Farquhar,

1989). Hence this percolation must be assessed for predicting the volume of

leachate. Even though there are no standards for the allowable rate of percolation

through landfill covers, the percolation rate is usually computed and then used to

predict impacts on the ground water as a part of the process of evaluating potential

health risks (Koerner and Daniel, 1997).

Currently, the common technique to assist in the estimation of leachate and design

of landfill cover profiles includes various computer simulation models used to

predict water balance. In the current research, the Hydrologic Evaluation of

Landfill Performance (HELP) program (Schroeder et al., 1994) was utilised for

water balance simulations. The primary purpose of this modelling was to assist in

the comparison of landfill design alternatives on the basis of water balances and

hydrologic performance.

The analysis was done by forward modelling intended to compare the variations

due to soil type in barrier layer simulated through a typical design process. By

forward modelling it is meant that simulations were performed without the benefit

of field data (Dwyer, 2003). The intent of forward simulations was to compare the

water balance of the landfill cover by varying the SWEPS mix properties.

The HELP program was selected because it is most popular industry software and

widely used in engineering practice around the world by landfill designers and is

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280

endorsed by the USEPA. Furthermore, it is routinely used for prescriptive cover

designs as well as alternative cover designs (Dwyer, 2003).

For the analysis, Visual HELP computer software was used. Visual HELP

combines the latest version of the HELP model (v.3.07) with an easy-to-use

interface and powerful graphical features for designing the model and evaluating

the modelling results. The latest version of the HELP model addresses many of

the limitations and bugs from earlier versions and also includes several new

analysis features (Waterloohydrogeologic Inc., 2005)

10.3.1 HELP model overview

A detailed engineering documentation of the HELP model algorithm used to route

water into different components of the water balance was provided by Schroeder

et al. (1994). Hence, a brief overview of HELP model relevant to earthen final

covers is provided here.

Figure 10.7 Schematic representation of water balance computations by

HELP program (Dwyer, 2003).

halla


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281

HELP program is a quasi-two-dimensional, deterministic, water routing model

used for determining water balances and was developed by the U.S. Army Corp of

Engineers for the United States Environmental Protection Agency (USEPA) (Qian

et al., 2002). HELP uses numerical solution techniques that account for the

effects of surface storage, snowmelt, runoff, infiltration, evapotranspiration,

vegetative growth, soil moisture storage, lateral subsurface drainage, leachate

recirculation, unsaturated vertical drainage, or leakage through soil,

geomembrane, or composite liners. A schematic of how HELP program handles

the water balance in a landfill final cover profile is shown in Figure 10.7.

The HELP program requires that each layer of the landfill cover to be categorised

by the hydraulic function that they perform. That is, they must be specified as a

vertical percolation layer, barrier soil liner, lateral drainage layer, or

geomembrane liner depending on the function and hydraulic properties of the

layer.

A vertical percolation layer generally has moderate to high saturated hydraulic

conductivity and unsaturated flow of water occurs in the vertical direction

(downward, due to gravity or upward, due to evapotranspiration). A barrier soil

layer has a low saturated hydraulic conductivity and is assumed to be fully

saturated (i.e. to have no capacity to store water without drainage occurring). A

lateral drainage layer has a relatively high hydraulic conductivity and is underlain

by a barrier layer. A lateral drainage layer allows for the vertical downward

movement of water similar to a vertical percolation layer, as well as lateral flow in

saturated zone at the base of the lateral drainage layer.

A modified version of the Soil Conservation Service (SCS) runoff curve number

method is used in HELP program to divide precipitation into runoff and

infiltration. The SCS runoff curve number used by HELP is based on the

hydraulic conductivity of the surface layer, condition of vegetation (i.e. Leaf Area

Index), as well as the slope and slope-length of the cover. If the air temperature is

� 0° C, precipitation is stored as a snow pack. The snow pack is allowed to melt

only when the air temperature rises above 0° C. The infiltrated water either

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282

remains in storage or is subjected to evapotranspiration, lateral drainage, and/or

percolation (Khire et al., 1997; Dwyer, 2003).

Water removal via evapotranspiration occurs from the evaporative depth of the

cover. A vertical percolation layer is the only type that allows for water removal

via evapotranspiration. Consequently, the evaporative depth of the cover cannot

be greater than the top vertical percolation layer. HELP provides default values

for evaporative depth based on the location of the site and the condition of the

vegetation. The quantity of water removed by evapotranspiration is computed

using an approach recommended by Ritchie (1972) and was a function of

potential evapotranspiration (PET) and the availability of water stored in the soil

profile. Potential evapotranspiration is calculated using a modified form of the

Penman (1963) equation.

If the layer is a vertical percolation layer, the water stored in the soil layer is

routed under a unit hydralulic gradient in the vertically downward direction

(Figure 10.7) using the unsaturated hydraulic conductivity (K�) computed by

Campbell’s (1974) equation. Evapotranspiration removes water from the vertical

percolation layer if the water content is above the permanent wilting pint (�wp).

The permanent wilting point is defined as the lowest amount of water that remains

in the soil because a plant is unable to extract it. Field capacity is the amount of

water in a wetted soil after it has drained. The size of the reservoir of water in a

soil that can be used by plants to maintain life is the moisture range between the

permanent wilting point and field capacity.

If the layer uses a barrier soil layer, the saturated hydraulic conductivity (Ks) and

the depth of ponded water on the surface of the barrier soil layer are used with

Darcy’s law to compute percolation (Figure 10.7). The soil’s saturated hydraulic

conductivity is used because the barrier layer is assumed to be fully saturated.

One major disadvantage of the HELP model, particularly in semi-arid and arid

climates, is that it does not model the surface evaporation and surface moisture

contents correctly and, hence, generally overestimates the infiltration and leachate

rates (Kodikara, 2001). Another limitation is the default values in SCS method are

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283

based on US climatic conditions. Their use in Australian conditions can influence

the results.

10.3.2 Input parameters for HELP simulation

HELP model is a well configured and user friendly computer program that

contains default values for most input parameters included within the software. To

simulate a typical design, many of the default parameters were utilised, except for

the properties of soil-EPS mix used as a barrier layer in the present research.

Various input parameters required for HELP program can be categorized into site

location, cover profile description, weather data, evapotranspiration data, soil data

and runoff data.

10.3.2.1 Site location

Brisbane, the capital of Queensland State in Australia was selected as the design

location. Brisbane is located on the south-east coast of Queensland. The latitude

and longitude of Brisbane are 27° 29’ S and 153° 08’ E respectively and the

elevation is 38 meters above sea level. The climate is considered as sub-tropical in

nature with wet, hot summers and cool, dry winters.

10.3.2.2 Cover profile description

Conventional compacted clayey cover systems consisting of a surface layer and a

barrier layer were selected. The depth of surface layer was taken as 0.30 m and the

depth of barrier layer was taken as 0.90 m. the surface layer was selected as sandy

loam and barrier layer was sand-bentonite (SB24) mix with and without EPS

beads.

10.3.2.3 Weather data

From the Bureau of Meteorology data (cited in Thorley and Boczek, 2000),

Brisbane’s annual rainfall is 1149 mm with annual extremes recorded of 411 mm

and 2242 mm. On an average, 592 mm, or 52% of the annual total rain falls

between the summer and autumn months of December to March. Average

monthly rain varies from 46 mm in August to 160 mm in January. Average rain

days are 122 per year, ranging from 6.7 in August to 13.5 in February. The annual

Chapter 10

284

extremes of recorded rain days, between 1840 and 1999, are 204 in 1887 with

only 52 recorded in 1865.

Mean daily temperatures for Brisbane range from maximums of 29.4° C in

January to 20.4° C in July, with minimum ranging from 20.7° C in January to 9.5°

C in July. The mean annual maximum is 25.5° C and the mean annual minimum

is 15.7° C. Average annual evaporation is 1648 mm, an excess of 499 mm over

annual rainfall. Mean daily evaporation rates range from 2.3 mm in June to 6.3

mm in December.

For the present study the GIS based in-built international weather generator (the

WHI weather generator) available in Visual HELP software, which can generate

statistically reliable weather for Brisbane for up to 100 years, was used. A review

of this data suggested that it is typical of what was cited in Thorley and Boczek

(2000). This weather generator utilises the weather generation algorithm

developed by the Agricultural Research Service of the U.S. Department of

Agriculture (USDA).

10.3.2.4 Vegetation data

The onset and termination of the plant growing season (allowable transpiration

period) for Brisbane was set to the default values of 357 and 317, respectively.

The Leaf Area Index (LAI) of 5 was used for all covers. This is the default value

for Brisbane and relates to fair strand of grass. A maximum evaporative zone

depth of 25 mm was used for all the covers.

10.3.2.5 Runoff data

The SCS runoff curve number was computed by the visual HELP program. It was

assumed that runoff was possible over 100% of the landfill area and a quality of

surface vegetation was of “Fair strand of grass”.

10.3.2.6 Soil properties

The surface layers and underlying compacted soil-EPS layers were input as

vertical percolation layer and barrier layer respectively. The surface layers were

input as vertical percolation layers because they were assumed vegetated

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285

(Schroeder et al, 1994). Furthermore, following the recommendation of Schroeder

et al (1994) low hydraulic conductivity layers were input as barrier layers.

The soil properties of sandy loam as a vertical percolation layer of were used from

default values available in the software (Table 10.2). However, the soil properties

of the barrier soil which is a soil-EPS mixes were calculated from the laboratory

data and were used in the calculations. The values are shown in Table 10.2.

Table 10.2 Properties of soils used.

Layer type Vertical percolation layer (Layer 1)

Barrier soil (Layer 2)

Soil type Sandy loam Soil – EPS mixes

EPS, % 0.0 0.3 0.6

Depth (m) 0.3 0.9 0.9 0.9

Porosity (vol/vol)

0.453 0.3586 0.3749 0.3884

Field capacity, (vol/vol)

0.19 0.2423 0.2449 0.2536

Wilting point, (vol/vol)

0.085 0.0697 0.1086 0.1397

Saturated hydraulic conductivity (cm/sec)

7.2E-4 1.18E-7 2.36E-7 1.25E-6

Water contents related to field capacity (corresponding to 33 kPa) and wilting

point (corresponding to 1500 kPa) for SWEPS mixes were obtained in the

laboratory using pressure-plate extractors. The saturated hydraulic conductivity

was measured from rigid wall compaction mould permeameter as described in

Section 10.1. The porosity was estimated from the swell pressure tests as

described below.

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286

In swell pressure test, as described in Chapter 7, the specimen was restrained

against swelling. That is, the volume was kept constant at all times with

increments in loading. Thus the variations in the water contents in soil and

SWEPS mix specimens were due to the voids present in the specimen and the

corresponding increase in swelling of the bentonite. The volume of water

occupied in the composite is the volume of voids.

10.3.3 Model results

The hydrological results generated by the HELP model include time series

information such as

• Precipitation

• Surface runoff

• Percolation or leakage through barrier layer

• Change in soil water storage

The design life of a landfill cover is feasible up to hundreds of years depending on

selection of materials, slope stability, resistance to erosion, adequate flow capacity

for internal drainage system and long term maintenance (McLaughlin and Skahn,

2000). Hence, the analysis was performed for 100 year duration to obtain the

annual average totals.

A summary of the results of the HELP simulation consisting of average annual

totals for years 1 through 100 is presented in Table 10.3. It can be noticed that

with the addition of EPS beads to the sand-bentonite mix, there is an increase in

the percolation or leakage from the barrier layer due to the increase in the

hydraulic conductivity. It can be recalled that the hydraulic conductivity of the

SWEPS mixes increased slightly with 0.3% EPS when compared with the control

soil and for 0.6% EPS a moderate increase (one order of magnitude) was

observed.

When compared with the control soil, the percolation or leakage through SWEPS

barrier layer increased by 73% and 353.52% for 0.3% and 0.6% EPS contents

respectively. This could be due to the addition of EPS which makes the water to

percolate probably through the interconnected networks, allowing less runoff and

evapotranspiration. Similarly, the water storage capacity of SWEPS is also

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287

reduced with the addition of EPS because of the impermeable nature of EPS beads

and the availability of less soil. For example, 0.6% of EPS content occupied

nearly 15% of composite volume. This can have an influence the water storage

capacity.

Table 10.3 Average annual totals for years 1 through 100 for Brisbane..

0.0% EPS 0.3% EPS 0.6% EPS Parameter

mm mm mm

Precipitation 1024.88 1024.88 1024.88

Runoff 80.41 70.82 36.40

Evaporation 906.07 887.48 812.30

Percolation/ Leakage through layer 2

39.59 66.78 176.52

Average head on top of layer 2

89.07 76.09 37.38

Change in water storage -0.184 -0.195 -0.326

It should be noted that the accuracy of input parameters is obviously critical for

acceptable output results. The forward simulations had known shortcomings with

the input parameters used. Many default parameters were utilised with the HELP

forward simulations rather than site specific data. Further, Dwyer (2003) stated

that HELP generally under-predicts the runoff. This under-prediction of surface

runoff leads to more water infiltration and consequently more percolation through

the cover. This could also be a reason in the present case.

Comparison of SWEPS landfill covers at different precipitation rates

To investigate whether precipitation can influence the percolation or leakage rates,

three other sites with varying precipitation rates were selected and a parametric

study was performed. The site location, weather data and vegetation data were

changed, but for the purpose of comparison, the cover profile, runoff data and soil

properties were unaltered. The sites are Cairns, Perth and Alice Springs in

Australia. These sites were considered to represent low to high precipitation rates.

The average annual precipitation rates for Cairns, Brisbane, Perth and Alice

Springs are 1724.58 mm, 1024.88 mm, 572.33 mm and 269.29 mm respectively.

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288

Table 10.4 shows the variation in site and vegetation parameters among these

sites. Annual average totals for years 1 through 100 for Cairns, Perth and Alice

Springs are shown in Tables 10.5 to 10.7.

Table 10.4 Variation in different parameters among different sites.

Latitude Longitude LAI Growing season Start day

Growing season end day

Average wind speed (km/h)

Evaporative zone depth

(cm)

Brisbane -27.374 151.903 5 357 317 12.87 25

Perth -31.836 114.025 3 27 2 25.74 38

Cairns -16.873 145.507 5 357 317 16.09 25

Alice springs -23.771 132.233 1 81 314 6.44 43

Table 10.5 Average annual totals for years 1 through 100 for Cairns.

0.0% EPS 0.3% EPS 0.6% EPS Parameter mm mm mm

Precipitation 1724.58 1724.58 1724.58 Runoff 615.66 597.04 465.68 Evaporation 1069.51 1062.18 1016.18 Percolation/ Leakage through layer 2

39.27 65.21 242.45


118.65 110.61 81.28

Change in water storage 0.123 0.146 0.258

Table 10.6 Average annual totals for years 1 through 100 for Perth.



11.25 21.15 65.46


31.99 28.98 12.72

Change in water storage 0.00 0.00 0.00

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289

Table 10.7 Average annual totals for years 1 through 100 for Alice Springs.



11.64 17.31 29.55


16.97 11.97 3.67

Change in water storage -0.123 0.04 0.04

From the Tables 10.5 to 10.7 it can be seen that precipitation rate has a significant

influence in the percolation or leakage through SWEPS barrier layers. Depending

on precipitation rate, there is relative increase in the percolation rate with the

addition of EPS. The percolation increase with the addition of 0.3% EPS is

varying from 50% to 88%, and for 0.6% EPS content the variation is from 150%

to 517% for the four sites analysed. In general, increased precipitation increases

the percolation rate as shown in Figure 10.8.

0

50

100

150

200

250

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

EPS, %

Ave

rage

ann

ual t

otal

per

cola

tion

rate

, mm

Cairns (precipitation = 1724.58 mm/year)Brisbane (precipitation = 1024.86 mm/year)Perth (precipitation = 572.33 mm/year)Alice Springs (precipitation = 269.29 mm/year)

Figure 10.8 Variation of average annual percolation rate with EPS content.

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290

The variations in the present study may also be due to the limitations in HELP

model in considering the physical processes that control unsaturated water

movement such as matric potential in soil barrier layers (Dwyer, 2003).

According to Dwyer (2003) HELP consistently under predicts the surface runoff

using SCS runoff method. Further, this method does not take into account a

rainstorm’s intensity or duration. Hence, actual field testing by considering the all

parameters are needed in understanding the accrual outcome with the SWEPS

landfill cover materials.

10.4 Summary

The results of hydraulic conductivity, compressibility and water balance analysis

are presented for one of the reconstituted expansive soil (SB24) with 0.0%, 0.3%

and 0.6% EPS contents. The addition of recycled EPS beads increased the

hydraulic conductivity in the soil. It was observed that the hydraulic conductivity

of the SWEPS mixes increases slightly with 0.3% EPS when compared with the

control soil, but with 0.6% EPS a moderate increase (one order of magnitude) is

observed. As previously mentioned, it is generally accepted that hydraulic

conductivity for a landfill liner or cover materials should be around 10-9 m/s or

less. While the control soil and soil with 0.3% EPS content may satisfy this

criterion, soil with 0.6% EPS content may only be used as a cover material e.g.

evapotranspiration cover.

Similarly, on compressibility characteristics it is noted that EPS beads inclusion

can make a SWEPS mix compressible. Hence, the addition of EPS to a soil may

potentially result in greater consolidation settlement. However, being a

lightweight material, SWEPS mixes exert less overburden pressure on the

underlying soils consequently resulting in less settlement.

Water balance analysis was performed using Visual HELP software with

statistically significant weather data. It revealed that the leakage or percolation

increases with increasing EPS content in the barrier soil owing to the increased

hydraulic conductivity of the SWEPS mix. Even though addition of EPS for

landfill cover applications shows an advantage in terms of desiccation control, the

increase in leachate rate needs consideration for its application. It needs further

analysis from field studies.

291

CHAPTER 11 - CONCLUSIONS AND RECOMMENDATIONS

The principal endeavour of this research was to assess the feasibility of reusing

waste EPS beads in geotechnical applications. Assessing the suitability of

recycled EPS beads for mass applications is of paramount importance for the

efficient and cost effective recycling of these waste products. Efforts have been

made to recycle the waste EPS products in various ways. However, it is rather

ironic that some valuable attributes of EPS products are also impediments to their

widespread recycling.

The use of pre-puff EPS beads in geotechnical applications is being practiced in

Japan for applications involving dredged soils at high moisture contents. In the

current research, the use of recycled EPS beads for geotechnical applications, for

controlling swell-shrink of expansive soils in particular, has been investigated.

This last chapter of the thesis concerns with the scientific contributions of the

research, the applicability of SWEPS mixes in geotechnical engineering and the

mix design criteria followed by conclusions of the various investigative exercises

undertaken during the course of this research program. The possible topics for

further research are also discussed.

11.1 Scientific contribution from this research

The following significant achievements may be claimed for this study:

• This research contributed to the minimisation of waste reaching to the landfill

thus promoting the quality of environment. It also promotes the sustainability

in construction through the recycling and reuse of waste materials.

• This research fulfilled the aim of developing Soil with EPS (SWEPS) mixes

and demonstrating its effectiveness in controlling of swell-shrink potential of

expansive soils.

• It demonstrated that EPS inclusion is influenced by the moulding moisture

content of the soil, and for optimum strength it is necessary to mix and

compact EPS beads at optimum moisture content of the soil.

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292

• It identified that EPS inclusion reduces the shear strength of soils and hence,

there is a need to incorporate chemical admixers. The combined lime-EPS

stabilisation has been found to be very effective in controlling the expansive

soil behaviour.

• This research is a significant step forward in the development of SWEPS

mixes for their bulk utilisation in geotechnical applications. This research

opens up further avenues for reuse of EPS beads in construction activities.

• The data generated in this research can form a basis for further research and

improvements in the development of SWEPS mixes. Furthermore, a modified

flowchart for lime-EPS stabilisation is suggested for engineering applications.

11.2 Engineering applications of this technique It is well known that for compacted clayey soils, compaction conditions affect the

swelling, shrinkage and desiccation behaviour of the soil. To reduce the swelling,

compaction on wet side of optimum is recommended (Holtz and Kovacs, 1981).

However, this wet side compaction contributes to the shrinkage and desiccation.

Hence, to reduce the cracking potential, compaction on the dry side is preferred

(Daniel and Wu, 1993). Because of the changing weather patterns around the

world, both compaction cases can produce unfavourable behaviour. Hence, there

is need to find other suitable alternatives.

Use of recycled EPS beads has been found to be an alternative admixer in

expansive soils to control the swell-shrink potential. To optimise the strength, if

no chemical stabiliser is added, EPS beads should be added to the soil at optimum

moisture content until a uniform and consistent mix is achieved. The mixing can

be done on-site using a concrete mixer or through a mixing plant using a pug mill.

However, it was observed that plant mixing is more effective than on-site mixing

(Miki, 1996) Field compaction can be done in the usual way, no additional

equipment is needed. While the EPS beads are compressed during compaction,

they can still have an influence on swelling and shrinkage due to its elastic

properties as demonstrated in Figure 11.1 for recycled EPS beads. It can be

inferred from the figure that when the bead is compressed the air inside the bead

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293

is decreased in volume but increased in pressure to maintain load equilibrium.

When the load is removed, the air void expands.

Figure 11.1 Compression and elastic rebound of recycled EPS beads upon loading and

unloading respectively. The potential application of this SWEPS mix can include backfill behind a

retaining wall, fill at the shoulder of pavements, and fill below concrete slabs

when there is a possibility of differential settlements. This technique is especially

suitable if differential swelling and settlements are expected. This technique may

also be used in landfill cover systems.

11.2.1 Backfill behind a retaining wall

The significant advantage gained because of the addition of EPS to the soil is the

considerable reduction in the dry unit weight of the composite thus formed for the

same moisture content. Thus it is suitable as a lightweight backfill material.

Furthermore, this reduction is particularly important in retaining walls as the

composite can be expected to produce less lateral force on the retaining wall. This

will allow the retaining wall to be made thinner.

The low value of compacted dry unit weight of SWEPS mix can result in greatly

increased stability for embankments built on weak soils. While it may not be

Chapter 11

294

relevant for Australian climatic conditions, the use of recycled EPS beads may

also result in reduced frost penetration due to their favourable thermal

characteristics when compared to other soils.

11.2.2 Pavements and shoulders

In pavements, equilibrium conditions will eventually be reached under the

pavements with respect to moisture content. However, because of the exposure to

weather elements, the pavement shoulders experience differential swelling and

shrinkage which can be cyclic in nature. In this situation, if soil mixed with EPS

beads is used for the shoulder, the movements can be taken care of.

Similarly, applications under for paving slabs where extreme movements due to

moisture variation can happen, this technique can prove to be a good option.

In paving applications, precaution should be taken in placing the SWEPS mix.

This composite material should not be placed as a top layer by itself. There should

be a sufficient cover above the SWEPS mix to take care of any chemical spillages

and UV degradation.

11.3 SWEPS Mix design criteria

Soils from one place may differ in imperative aspects from the soils tested at other

locations, climatic conditions and soil type (Basha et al., 2005). The complexity in

soil conditions and the differences in soil properties make it necessary in each

case to resolve the problem by adopting some form of mix design instead of

adopting a generic approach. Because of the variabilities in the index properties of

different soils it was not possible to produce a stand-alone model or equation

which is applicable to all soil types across all EPS contents. Furthermore, it was

noticed in scoping studies (Chapter 5) that the addition of EPS beads depends on

the moulding moisture content of the soil. Hence, instead of a design formula, a

mix design procedure is provided for the application of this technique to a much

broader range of situations.

A mix design criteria modified from Thomspon (1970) is suggested. It is basically

used in the mix design of lime stabilised soils for pavements. The same was

modified by incorporating EPS content as another factor.

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295

Figure 11.2 Flow chart for the mix design of SWEPS mixes (modified after Thompson, 1970).

The primary objective of this mixture design is to identify an optimum EPS and

stabiliser content based on the strength criteria that is a function of the how the

Determine clay content

Determine optimum moisture content

Select binder type

Find optimum lime content

Select between 2 to 6%

Determine EPS content based on

homogeneous mixture at OMC

Fix EPS content and/or binder content

Determine density of the composite

Determine CBR and/or UCS

Find swelling and shrinkage

Accept binder content and EPS application rate

depending up on field application

Change binder content

Increase moisture

content until workability is

achieved

Strength Requirement

No Yes

Lime Cement

OK

Not OK

OK

Not OK

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296

composite will be used; as a backfill material, a compacted fill material or a

landfill cover material. Blending recycled EPS beads with chemical admixer can

produce even more significant effect while still providing a cost effective solution.

To optimise the density and strength with the addition of EPS beads and lime,

density tests, California Bearing Ratio (CBR) and Unconfined Compressive

Strength (UCS) tests can be performed. Figure 11.2 shows the mix design

approach, which depends on the strength criteria. The selection of the material

depends on the strength to be gained, which is a function of the optimum moisture

content and optimum lime content. The addition of EPS beads at optimum

moisture content needs to be considered prior to testing for the strength criteria.

11.4 Conclusions from this research

As an original research, this investigation was unavoidably exploratory in nature

and primarily conceived based on a hypothesis that recycled EPS beads can be

used for geotechnical applications as a swell-shrink modifier of expansive soils or

as a landfill cover material. More than just focussing on the modification of the

soil’s swell-shrink characteristics, the influence of recycled EPS beads on the

overall behaviour of the soil was also investigated by performing compaction,

strength, desiccation, hydraulic conductivity and compressibility tests.

This research is a step forward in the significant use of recycled EPS beads in

geotechnical applications. This research opens up other possible avenues for the

reuse of EPS in bulk quantities. The following conclusions can be drawn from this

study.

• The most advantageous properties of EPS (lightweight and non-

decomposable) create a major hindrance in recycling. Most of the EPS

recycling efforts have been focussed on mechanical, chemical and thermal

methods. However, the current system in practice for collection, sorting and

reclamation of EPS products are too costly, mainly because they are small in

scale and extremely labour intensive. Furthermore, these methods require

energy to a greater extent while the rate of recycling is low. Hence, in this

research, possible large scale recycling options for geotechnical applications

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297

such as swell-shrink modifier, desiccation crack controller were evaluated

using a dredged soil and reconstituted expansive soils by mixing EPS beads.

• This research evaluated the recyclability and miscibility factors that control

the mixing of EPS beads with soils through preliminary studies with a dredged

soil at optimum moisture content. Among other things, how the moulding

moisture content influences the addition of EPS beads was investigated. It was

observed that with higher moisture content, more EPS can be added into the

soil. For example, at 39% of moulding moisture content (which is optimum

moisture content for this soil) a maximum quantity of 1.25% of EPS can be

added. Whereas increasing the moulding moisture content to 50% resulted in

3% EPS content as the maximum possible quantity. In addition, the influence

of EPS on the unit weight and strength of the dredged soil was also

investigated. It was noticed that EPS inclusion reduces the unit weight but

decreases the strength of the soil. The results established the technical

feasibility and the potential beneficial use of recycled expanded polystyrene as

a soil modifier.

• In continuation, the influence of recycled EPS beads on the swell-shrink

properties of expansive soils was investigated through the use of artificially

reconstituted expansive soils made by mixing fine sand and sodium bentonite.

Three different soils notated as SB16, SB24 and SB32 representing 16%, 24%

and 32% of bentonite contents respectively were selected. These soils also

represent soils of low, medium and high plasticity indices. It was observed

that the use of recycled EPS beads as an admixer leads to the reduction in

magnitude of swelling and shrinkage of expansive soils. For example, in

absolute terms, when compared with the free swell of control soil, the increase

in EPS content from 0.3% to 0.9% caused a reduction in free swell form 10 to

63% for SB16, 13 to 50% for SB24 and 13 to 48% for SB32 soils

respectively. Furthermore, this research also demonstrated that the reduction

of swelling and shrinkage is primarily caused by replacement of soil particles

as well as the elasticity of the EPS beads.

Chapter 11

298

• The strength characteristics of the test soils with the addition of EPS beads

were studied using unconsolidated-undrained triaxial tests. It was observed

that strength reduces with the addition of recycled EPS beads because of the

compressible nature of EPS beads. Hence, for improving the strength of the

composite, chemical stabilisers are needed.

• Limited studies on suction, hydraulic conductivity, desiccation of the SWEPS

mixes were conducted to investigate their overall behaviour. Based on the

results, it can be concluded that suction and hydraulic conductivity increase

whereas desiccation decreases with the addition of EPS beads.

• Water balance analysis was performed using Visual HELP software with

statistically significant weather data. It revealed that the leakage or percolation

increases with increasing EPS content in the barrier soil owing to the

increased hydraulic conductivity of the SWEPS mix. Even though addition of

EPS for landfill cover applications shows an advantage in terms of desiccation

control, the increase in leachate rate needs consideration for its application. It

needs further analysis from field studies

11.5 Recommendations for further studies

Considering that this research is the first in the use of EPS to control swell-shrink

potential of expansive soils, there is ample scope for further investigations or

development. Based on the results of the present investigation, the following

recommendations are made for further research and advancement in the use of

recycled EPS beads in geotechnical applications.

• In the present investigation the recycled EPS beads selected were in the range

of 3 to 9 mm in size. Hence, the effect of EPS gradation variation on the

swell-shrink behaviour of expansive soils should be investigated in the future.

• There is research going on in many parts of the world to study the use

industrial by-products such as fly ash, slag etc. for their bulk utilisation in

geotechnical applications. Research can therefore be conducted by mixing

Chapter 11

299

recycled EPS beads with those industrial by-products to enhance or

compliment their behaviour for their mass use in geotechnical applications.

• Influence of virgin EPS beads on the swelling properties of expansive soils

can also be investigated in lieu of recycled EPS beads. The recycled EPS

beads are irregular shape whereas virgin beads are circular in shape.

Consequently, it is important to compare the performance of these two types

of beads.

• The influence of sand fraction and recycled EPS beads on the swell-shrink

behaviour of expansive soils can also be evaluated.

• Large scale field investigation can be conducted to test for an effective field-

scale mixing techniques and also to observe the behaviour of SWEPS mixes

for desiccation control of landfill cover systems.

• At this juncture it is important to note that although limited small-scale

experimental investigations can provide useful observations in comparative

analysis for the variabilities observed; these smaller scales did not replicate

the heterogeneities that can dominate performance such as the case in natural

expansive soils or actual landfill covers. Hence, SWEPS mix technique needs

to be tested on pilot scale before embarking on further applications.

• Even though the use of EPS as geofoam blocks in geotechnical engineering

spanning over 20 years shows its durability, the long term behaviour as

affected by chemical and other environmental factors have not been fully

investigated in this study. These issues should be investigated in the future.

Chapter 11

300

301

REFERENCES ___________________________________________________________ Ahmad, S. A. and Peaker, K. R. (1977), “Geotechnical properties of soft marine Singapore clay,” Geotechnical Aspects of Soft Clays, Brenner, R. P. and Brand, E. W. (Eds.), Bangkok: Asian Institute of Technology, pp. 3-14. Albrecht, B. (1996), “Effect of desiccation on compacted clay,” MS thesis, University of Wisconsin, Madison, Wisconsin, U.S.A. Albrecht, B. A. and Benson, C. H. (2001), “Effect of desiccation on compacted natural clays,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 1, pp. 67-75. Al-Homoud, A. S., Basma, A. A., Malkawi, A. I. H. and Al-Bashabsheh, M. A. (1995), “Cyclic swelling behaviour of clays,” Journal of Geotechnical Engineering, ASCE, Vol. 121, No. 7, pp. 562-565. Al-Khafaf, S. and Hanks, R. J. (1974), “Evaluation of the filter paper method for estimating soil water potential”, Soil Science, Vol. 117, No.4, pp.194-199. Allam, M. M. and Sridharan, S. (1981), “Effect of wetting and drying on shear strength,” Journal of Geotechnical Engineering Division, ASCE, Vol. 107, No. 4, pp. 421-438. Alliance of Foam Packaging Recyclers (2001), “Recycled content in expandable polystyrene foam protective packaging,” Technical Bulletin, Crofton, MD 21114. Al-Omari, R. R. and Hamodi, F. J. (1991), “Swelling resistant geogrid – a new approach for the treatment of expansive soils,” Geotextiles and Geomembranes, Vol. 10, pp. 295-317. Al-Tabbaa, A. and Aravinthan, T. (1998), “Natural clay – shredded tire mixtures as landfill barrier materials,” Waste Management, Vol. 18, No. 1, pp. 9-16. Al-Wahab, R. M. and El-Kedrah, M. A. (1995), “Using fibers to reduce tension cracks and shrink/swell in a compacted clay,” Geoenvironment 2000, Geotechnical special publication No. 46, ASCE, New York, pp. 791-805. Ambrosanio, A. (1955), “The use and application of bentonite in construction practice”, Department of Geotechnical Engineering, University of Naples, Naples, Italy, Report 92a (In Italian). Andersland, O. B. and Khattack, A. S. (1979), “Shear strength of kaolonite/fibre soil mixture,” Proceedings of First International Conference on Soil Reinforcement, Vol. I, Paris, France, pp. 11-16. ANZECC (1992), “Australian water quality guidelines for fresh and marine water,” National water quality management strategy paper No. 4, Australia and New Zealand Environment and Conservation Council, Canberra.

References

302

AS 1141.51 - 1996, “Methods for sampling and testing aggregates – Unconfined compressive strength of compacted materials,” Standards Australia. AS 1289.2.1.1 - 1992, “Methods of testing soils for engineering purposes, Method 2.1.1: Soil moisture content tests – Determination of the moisture content of a soil – Oven drying method (standard method),” Standards Australia. AS 1289.3.1.1 - 1995, “Methods of testing soils for engineering purposes, Method 3.1.1: Soil classification tests – determination of the liquid limit of a soil – Four point Casagrande method,” Standards Australia. AS 1289.3.2.1 - 1995, “Methods of testing soils for engineering purposes, Method 3.2.1: Soil classification tests – Determination of the plastic limit of a soil – Standard method,” Standards Australia. AS 1289.3.4.1 - 1995, “Methods of testing soils for engineering purposes, Method 3.4.1: Soil classification tests – Determination if the linear shrinkage of a soil – Standard Method,” Standards Australia. AS 1289.3.5.1 - 1995, “Methods of testing soils for engineering purposes, Method 3.5.1: Soil classification tests – determination of the soil particle density of a soil – Standard method,” Standards Australia. AS 1289.3.5.2 - 2002, “Methods of testing soils for engineering purposes, Method 3.5.2: Soil classification tests – determination of the soil particle density of combined soil fractions – Vacuum pycnometer method,” Standards Australia. AS 1289.3.6.3 - 2003, “Methods of testing soils for engineering purposes, Method 3.6.3: Soil classification tests – Determination of the particle size distribution of a soil – Standard method of fine analysis using a hydrometer,” Standard Australia. AS 1289.4.1.1 - 1997, “Methods of testing soils for engineering purposes, Method 4.1.1: Soil chemical tests – Determination of the organic matter content of a soil – Normal method,” Standards Australia. AS 1289.5.1.1 - 2003, “Methods of testing soils for engineering purposes, Method 5.1.1: Soil compaction and density tests – Determination of the dry density /moisture content relation of a soil using standard compactive effort,” Standards Australia. AS 1289.6.1.1 - 1998, “Methods of testing soils for engineering purposes, Method 6.1.1: Soil strength and consolidation tests – Determination of the California Bearing Ratio of a soil – Standard laboratory method for a remoulded specimen,” Standards Australia. AS 1289.6.2.2 - 1998, “Methods of testing soils for engineering purposes, Method 6.2.2: Soil strength and consolidation tests – Determination of the shear strength of a soil – Direct shear test using shear box,” Standards Australia.

References

303

AS 1289.6.4.1 - 1998, “Methods of testing soils for engineering purposes, Method 6.4.1: Soil strength and consolidation tests – Determination of the compressive strength of a soil – Compressive strength of a saturated specimen tested in undrained triaxial compression without measurement of pore water pressure,” Standards Australia. AS 1289.6.6.1 - 1998, “Methods of testing soils for engineering purposes, Method 6.6.1: Soil strength and consolidation tests – Determination of the one-dimensional consolidation properties of a soil – Standard method,” Standards Australia. AS 1289.6.7.2 - 2001, “Methods of testing soils for engineering purposes, Methods 6.7.2: Soil strength and consolidation tests – Determination of permeability of a soil – Falling head method for a remoulded specimen,” Standards Australia. AS 1289.7.1.1 - 2003, “Methods of testing soils for engineering purposes, Method 7.1.1: Soil reactivity tests – Determination of the shrinkage index of a soil – shrink-swell index,” Standards Australia. AS 1366.3 – 1992, “Rigid cellular plastics sheets for thermal insulation. Part 3 – Rigid cellular polystyrene – moulded (RC/PS-M)”. Standards Australia. AS 1726 – 1993, “Geotechnical site investigations,” Standards Australia. AS 4489.6.1 - 1997, “Test methods for limes and lime stones, Method 6.1: Lime index – Available lime,” Standards Australia. ASTM D 559 (2003), “Wetting and drying of compacted soil-cement mixtures”, Annual book of ASTM Standards, 04.08, ASTM International, West Conshohocken, PA ASTM D 5298 (2003), “Standard test method for measurement of soil potential (suction) using filter paper,” Annual book of ASTM Standards, 04.08, ASTM International, West Conshohocken, PA Athanasopoulos, G. A. (1997), “Results of direct shear tests on geotextile reinforced cohesive soils”, Geotextiles and Geomembranes, Vol. 14, pp. 619-644. Babu, D. S., Babu, K. G. and Wee, T. H. (2005), “Properties of lightweight expanded polystyrene aggregate concrete containing fly ash,” Cement and Concrete Research, Vol. 35, pp. 1218-1223. Bagon, C. and Frondistous-Yannnas, S. (1976), “Marine floating concrete made with polystyrene beads,” Magazine of Concrete Research, Vol. 28, pp. 225-229

References

304

Bao, C. G. and Liu, T. H. (1988), “Some properties of shear strength on Nanyang expansive clay,” Proceedings of the international conference on engineering problems of regional soils, Beijing, China, International Academic publishers, Pergamon press, pp. 543-546. BASF (1998), “Rigid styropor foam as a lightweight construction BASF material for highway foundations: Geofoam,” Technical Information – Styropor TI 1- 800, BASF plastics,, Ludwigshafen, Germany Basha, E. A., Hashim, R., Mahmud, H. B. and Muntohar, A. S. (2005), “Stabilization of residual soil with rice husk ash and cement,” Construction and Building Materials, Vol. 19, pp. 448-453. Basma, A. A., Al-Homoud, A. S., Malkawi, A. I. H. and Al-Bashabsheh, M. A. (1996), “Swelling- shrinkage of natural expansive soils,” Applied Clay Science, Vol.11, pp. 211-227. Basma, A. A., Al-Rawas, A. A., Al-Saadi, S. N. and Al-Zadjali, T. F. (1998), “Stabilisation of expansive clays in Oman,” Environmental and Engineering Geosciences, Vol. IV, No.4, pp. 503-510. Beinbrech, G. (1996), “Current status of Geofoam construction method in Germany,” Proceedings of International symposium on EPS construction Method, EPS TOKYO’96, Japan, pp. 118-127. Bell, F. G. (1996), “Lime stabilisation of clay minerals and soils,” Engineering Geology, Vol. 42, pp. 223-237. Benson, C. H., Abichou, T. H., Olsen, M. A. and Bosscher, P. J. (1995), “Winter effects on hydraulic conductivity of compacted clay”, Journal of Geotechnical Engineering, ASCE, Vol. 121, No. 1, pp. 69-79. Benson, C., Abichou, T., Albright, W., Gee, G., and Roesler, A. (2001), “Field evaluation of alternative earthen final covers,” International Journal of Phytoremediation, Vol. 3, No. 1, pp. 105-127. Bergado, D. T., Chai, J. C., Alfaro, M. C. and Balasubramaniam, A. S. (1994), “Improvement techniques of soft ground in subsiding and lowland environment,” Rotterdam: Balakema. Bergado, D. T., Anderson, L. R, Miura, N. and Balasubramaniam, A. S (1996), “Soft ground improvement in lowland and other environments,” New York: ASCE press. Bhattacharja, S., Bhatty, J.I. and Todres, H.A. (2003), “Stabilisation of clay soils by Portland cement or lime – a critical review of literature”, PCA R&D serial No. 2066, Portland Cement Association, Skokie, Illinois, USA.

References

305

Bilsel, H. and Tuncer, E.R. (1998), “Cyclic swell-shrink behaviour of Cyprus clay,” Proceedings of an International symposium on Problematic soils, Sendai, Japan, Vol.1, pp. 337-340. Bishop, A.W. and Henkel, D.J. (1962), “The measurement of soil properties in the triaxial test,” London: Edward Arnold ltd. Borgesson, L. (1990), “Laboratory testing and computer simulation of clay barrier behaviour,” Proceedings of 9th international clay conference, AIPEA, Strasbourg 1989, Sci. Geol. Mem.87, pp.117-126. Boynton, S. S. and Daniel, D. E. (1985), “Hydraulic conductivity tests on compacted clay,” Journal of Geotechnical Engineering, ACSE, Vol. 11, No. 4, pp. 465-478. Bradford, A. T. (1978), “Structures in expansive clay,” Seminar on foundations in expansive clay soils, Resource materials centre, DDIAE, Darling Downs, pp. 2-4. Brandl, H. (1981), “Alteration of soil parameters by stabilisation with lime”, Proceedings of 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, Vol.3, pp 587-594. Broms, B.B. and Boman, P. (1979), “Stabilisation of soil with lime columns”, ground engineering, Vol.12, No.4, pp 23-32. Bronswijk, J. J. B. and Ever-Vermeer, J. J. (1990), “Shrinkage of Dutch clay soil aggregates,” Netherlands Journal of Agricultural Science, Vol.38, pp. 175-194. Brown, R.G. (2000), “Road construction and road embankment repair with ultra lightweight polystyrene”, Proceedings of GeoEng2000, Melbourne, Vic, Australia, Vol1, pp 407 (full paper on CD-Rom). BS 5930 (1999), “Code of practice for site investigation”, London: British Standards Institute. Bullen, F. (2002), “Design and construction of low cost, low – volume roads in Australia,” Transportation Research Record, No. 1819, pp. 173-179. Bulut, R., Park, S. W. and Lytton, R.L. (2000), “Comparison of total suction values from psychrometer and filter paper methods,” Unsaturated soils for Asia, Rahardjo, H., Toll, D. G. & Leong, E. C. (Eds.), Rotterdam: Balkema, pp.269-273. Campbell, G. S. (1974), “A simple method for determining unsaturated hydraulic conductivity from moisture retention data,” Soil Science, Vol. 117, No.6, pp. 311-314. Chakrabarti, S. and Kodikara, J.K. (2007), “Direct tensile failure of cementitiously stabilised crushed rock materials”, Canadian Geotechnical Journal, Vol. 44, No. 2, pp. 231-240.

References

306

Chalermyanont, T. and Arrykul, S. (2005), “Compacted sand-bentonite mixtures for hydraulic containment liners,” Songklanakarin Journal of Science and Technology, Vol. 27, No. 2, pp. 313-323. Chandler, R. J., Crilly, M. S. and Montgomery-Smith, G. (1992), “A low cost method of assessing clay desiccation for low rise buildings,” Proceedings of Institution of Civil Engineers, Vol. 92, No.2, pp. 82-89. Chapuis, R. P. (2002), “The 2000 R.M. Hardy lecture: Full –scale hydraulic performance of soil-bentonite and compacted clay liners,” Canadian Geotechnical Journal, Vol.39, pp. 417-439. Chen, F. H. (1988), “Foundations on expansive soils,” Developments in geotechnical engineering Vol.54, Amsterdam: Elsevier science publishing. Chen, X. Q., Lu, Z. W. and He, X. F. (1985), “Moisture movement and deformation of expansive soils,” 11th International conference on soil mechanics and foundation engineering, Vol. 4, San Francisco, California, pp. 2389-2392. Chen, F. H. and Ma, G. S. (1987), “Swelling and shrinkage behaviour of expansive clays,” 6th International conference on Expansive soils, Vol.1, New Delhi, India, pp. 127-129. Chu, T. Y. and Mou, C. H. (1973), “Volume change characteristics of expansive soils determined by control suction tests,” Proceedings of 3rd International Conference on Expansive Soils, Vol. 1, Haifa, Israel, pp. 177-185. Chu, T.Y. and Mou, C. H. (1981), “Soil-suction approach for evaluation of swelling potential”, Transportation Research Record, No. 790, pp. 54-60. Cocka, E. (2001), “Use of class C fly ash for the stabilisation of an expansive soil,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 7, pp. 568-573. Cocka, E. and Yilmaz, Z. (2004), “Use of rubber and bentonite added fly ash as a liner material,” Waste Management, Vol. 24, pp. 153-164. Colina, H. and Roux, S. (2000), “Experimental model of cracking induced by drying shrinkage,” The European Physical Journal E, Vol.1, pp. 189-194. Consoli, N. C., Prietto, P. D. M. and Ulbriuch, L. A. (1998), “Influence of fiber and cement addition on behaviour of sandy soil,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 124, No. 12, pp. 1211-1214. Cook, D. J. (1983), “Expanded polystyrene concrete,” In: Swamy, R.N. editor, Concrete technology and design. New concrete materials, Vol.1, London: Surrey University press, pp. 41-69.

References

307

Corte, A. and Higashi, A. (1960), “Experimental research on desiccation cracks in soil”, U.S. Army Snow Ice and Permafrost Research Establishment, Research Report No.66, Corps of Engineers, Wilmette, Illinois, U.S.A. Dakshinamurthy, V. (1978), “A new method to predict swelling using hyperbola equation,” Geotechnical Engineering, Journal of South East Asian Society of Soil Engineering, Vol. 9, pp. 29-38. Daniel, D. E. and Benson, C. H. (1990), “Water content- density criteria for compacted soil liners,” Journal of Geotechnical Engineering, ASCE, Vol. 116, No. 12, pp. 1811-1830. Daniel, D. E. and Wu, Y. K. (1993), “Compacted clay liners and covers for arid sites,” Journal of Geotechnical Engineering, ASCE, Vol. 119, No.2, pp. 223-237. Das, B. M. (2005), “Fundamentals of geotechnical engineering,” Toronto, Ontario: Thomson. Day, R. W. (1994), “Swell-shrink behaviour of compacted clay,” Journal of Geotechnical Engineering, ASCE, Vol. 120, pp. 618-623. Day, R. W. (2006), “Foundation engineering handbook,” McGraw-Hill Publishing companies. De Magistris, F. P., Silvestri, F. and Vinale, F. (1998), “Physical and mechanical properties of a compacted silty sand with low bentonite fraction,” Canadian Geotechnical Journal, Vol.35, pp. 909-925. Den Haan, E. J. (1998), “Cement based stabilisers for Dutch organic soils,” Problematic soils, Yanagisawa, Moroto & Mitachi (Eds.), Rotterdam: Balkema, pp. 53-56. Desai, I. D. and Oza, B. N. (1997), “Influence of anhydrous calcium chloride on shear strength of clays,” Symposium on expansive soils, Vol.1, pp. 17-25. Diamond, S. and Kinter, E. (1966), “Adsorption of calcium hydroxide by montmorillonite and kaolinite,” Journal of Colloid Interface Science, Vol. 22, pp. 240-249. Dif, A. F. and Blumel, W. F. (1991), “Expansive soils with cyclic drying and wetting,” Geotechnical Testing Journal, ASTM, Vol. 14, pp. 96-102. Dorp, T. V. (1996), “Building on EPS geofoam in the low lands experiences in the Netherlands,” Proceedings of International symposium on EPS construction method, EPS TOKYO’96, Japan, pp. 60-69. Drumm, E., Boles, D. and Wislon, G. (1997), “Desiccation cracks result in preferential flow,” Geotechnical News, Vol. 15, No. 2, pp. 22-25.

References

308

Du, Y. J. and Hayashi, S. (2000), “Study on the swell properties and soil improvement of compacted expansive soils,” Unsaturated soils for Asia, Rahardjo, H., Toll, D. G. & Leong, E. C. (Eds.), Rotterdam: Balkema, pp. 639-644. Duskov, M. (1996), “3-D finite element analyses of pavement structures with an EPS Geofoam sub-base,” Proceedings of International symposium on EPS construction Method, EPS TOKYO’96, Japan, pp. 48-57. Dwyer, S. F. (2003), “Water balance measurements and computer simulations of landfill covers”, Ph. D. thesis, The University of New Mexico, Albuquerque, New Mexico. Eades, J. L and Grim, R. E. (1966), “A quick test to determine lime requirements for soil stabilization,” Highway Research Board, No. 139, pp. 61-72. Edil, T. B. (2004), “A review of mechanical and chemical properties of shredded tires and soil mixtures,” Recycled materials in geotechnics, ASCE geotechnical special publication no 127, Aydilek, A.H. and Wartman, J. (eds), EDO (2003), “Technical reports of construction method using expanded polystyrol,” EPS Development Organisation, Tokyo. Eighmy, T. T. and Magee, B. J. (2001), “The road to reuse,” Civil Engineering, ASCE, Vol. 7, No. 9, pp. 66-71 and 80-81. El-Sohby, M. A. (1994), “Swelling and collapsible behaviour of arid soils,” Proceedings of symposium on developments in Geotechnical Engineering, Bangkok, Thailand, pp. 193-199. El-Sohby, M.A., Ossama Mazen, S. and Tarek F. Abdil, M. (1988), “Evaluation of free swell test measurements,” Proceedings of the international conference on engineering problems of regional soils, Beijing, China, International Academic publishers, Pergamon press, pp. 568-571. El-Sohby, M. A. and Rabba, E. A. (1981), “Some factors affecting swelling of clayey soils,” Geotechnical Engineering, Vol.12, pp. 19-39. Elshorbagy, W. A. and Mohamed, A. M. O. (2000), “Evaluation of using municipal solid waste compost in landfill closure caps in arid areas,” Waste Management, Vol. 20, pp. 499-507. Esch, D. C. (1995), “Long-term evaluations of insulated roads and airfields in Alaska,” Transportation Research Record, No. 1481, pp. 56-62. Fan, J.S. and Yang, C.B. (1988), “On the characteristics of expansive soil in Heifei, China,” Proceedings of the international conference on engineering problems of regional soils, Beijing, China, International Academic publishers, Pergamon press, pp. 572-575.

References

309

Fang, H. –Y. (1997), “Introduction to Environmental Geotechnology,” Boca Raton, New York: CRC press. Fang, H. -Y. and Owen, D. T. Jr. (1977), “Fracture-swelling-shrinkage behaviour of soft marine clays,” Geotechnical Aspects of Soft Clays, Brenner and Brand (Eds.), Bangkok: Asian Institute of Technology, pp. 15-25. Farquhar, G. (1989), “Leachate: production and characterisation,” Canadian Journal of Civil Engineering, Vol.16, pp.317-325. Fisher, K. (2000), “The expanded polystyrene industry group action plan, incorporating produce box manufacturers throughout Australia,” EPS Industry coordinator, Plastics and Chemicals Industries Association (PACIA), Victoria, pp. 1-33. Fletcher, C. S. and Humphries, W. K. (1991), “California bearing ratio improvement of remoulded soils by the addition of polypropylene fiber reinforcement,” Transportation Research Record, No. 1295, pp. 80-86. Foose, G. J., Benson, C. H. and Bosscher, P. J. (1996), “Sand reinforced with shredded waste tires,” Journal of Geotechnical Engineering, ASCE, Vol. 122, No. 9, pp. 760-767. Fredlund, D. G. and Rahardjo, H. (1993), Soil mechanics for unsaturated soils, New York: Wiley. Frydenlund, T. E. and Aaboe, R. (1996), “Expanded polystyrene – the light solution,” Proceedings of International Symposium on EPS Construction Method, EPS TOKYO’96, Japan, pp. 32-46. Gartung, E. and Zanzinger, H. (1998), “Engineering properties and uses of geosynthetic clay liners”, in Geotechnical Engineering of Landfills, (Eds.) Dixon, N., Murray, E.J. and Jones, D. R., London : Thomas Telford, pp 131- 149. Gates, W. P., Anderson, J. S., Raven, M. D. and Churchman, G. J. (2002), “Mineralogy of a bentonite from Miles, Queensland, Australia and characterisation of its acid activation products,” Applied Clay Science, Vol. 20, pp. 189-197. Ghazavi, M. and Sakhi, M. A. (2005), “Influence of optimised tire shreds on shear strength parameters of sand”, International Journal of Geomechanics, ASCE, Vol.5, No. 1, pp. 58-65. Gilchrist, H. G. (1963), “A study on volume change of a highly plastic clay,” M.Sc. Thesis, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, 141 pp. Gleason, M. H., Daniel, D. E. and Eykholt, G. R. (1997), “Calcium and sodium bentonite for hydraulic containment applications,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 123, No. 5, pp. 438-447.

References

310

Goodhue, M. J., Edil, T. B. and Benson, C. H. (2000), “Interaction of foundry sands with geosyntehtics,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 4, pp. 353-362. Gosaburo, M. (1996), “EPS construction methods in Japan,” Proceedings of International symposium on EPS construction method, Japan, pp. 2-7. Gosavi, M., Patil, K. A., Mittal, S. and Saran, S. (2004), “Improvements of properties of black cotton soil subgrade through synthetic reinforcement,” Journal of Institute of Engineers (India), Vol. 84, pp. 257-262. Gourley, C. S. and Schreiner, H. D. (1995), “Filed measurement of soil suction”, Unsaturated soils, Alonso and Delege (Eds.), Rotterdam: Balkema, pp. 601-607. Graham, J., Saadat, F., Gray, M. N., Dixon, D. A. and Zhang, Q.-Y. (1989), “Strength and volume change behaviour of a sand – bentonite mixture,” Canadian Geotechnical Journal, Vol. 26, pp. 292-305. Gray, D. and Ohashi, H. (1983), “Mechanics of fiber reinforcement of sand,” Journal of Geotechnical Engineering, ASCE, Vol. 109, No.3, pp. 335-353 Greacen, E. L., Walker, G. R. and Cook, P.G. (1987), “Evaluation of the filter paper method for measuring soil water suction,” International conference on measurement of soil and plant water status, pp. 137-143. Grim, R. and Guven, N. (1978), “Bentonite: Geology, mineralogy, properties and uses,” New York: Elsevier science publishing. Gulin, K. and Wilstrom, R. (1997), “Stabilisation of horizontal movements in weak organic clay layers,” Proceedings of the 14th ICSMFE, Hamburg, Germany, pp. 1689-1692. Hamblin, A. P. (1981), “Filter-paper method for routine measurement of field water potential,” Journal of Hydrology, Vol. 53, pp. 355-360. Hamilton, J. J. (1977), “Foundations on swelling or shrinking subsoils,” CBD-184, Canadian Building Digest, National Research Council, Canada. Hanna, A. N. (1978), “Expanded polystyrene concrete subbases”, Transportation Research Record, No. 675, pp. 1-6. Hayashi, Y., Suzuki, A. and Kitazono, Y. (1998), “Effect of soil properties on the improvement with foam and cement milk”, Environmental Geotechnics, Rotterdam: Balkema, pp. 637-642. Head, K. H. (1994), “Manual of soil laboratory testing, Volume 1, soil classification and compaction tests,” London: Pentech press.

References

311

Hey, K. M. (1999), “Desktop assessment and use of on-site indicators s preliminary methods for recognition of acid sulphate soils”, In Acid Sulphate soils and their management in coastal Queensland, Hey, K.M., Ahern, C.R., Eldershaw, V.J., Anorov, J.M. and Watling, K.M. (Eds.), Brisbane 21-23, April, 1999, Department of Natural resources, Indooroopilly, Queensland, Australia. Hillmann, R. (1996), “Research projects on EPS in Germany: Material behaviour and full scale model studies,” Proceedings of International symposium on EPS construction Method, EPS TOKYO’96, Japan, pp. 106-115. Hirasawa, M., Saeki, S., Kodama, S. and Yakuwa, T. (2000), “Development of light-weight soil using excavated sand and its application for harbour structures in cold regions,” Nakase & Tschida (eds), Coastal geotechnical engineering in practice, Rotterdam: Balkema, pp. 697-702. Hoare, D. J. (1979), “Laboratory study of granular soils reinforced with randomly oriented discrete fibres,” Proceedings of the International conference on soil reinforcement: reinforced earth and other techniques, Vol. 1, Paris, France, pp. 47-52. Hoikkala, S., Leppanen, M. and Tanska, H. (1997), “Block stabilisation of peat in road construction,” Proc. Of the 14th ICSMFE, Hamburg, Germany, pp. 1693-1696. Holtz, R. D. and Kovacs, W. D. (1981), “An introduction to geotechnical engineering”, Upper Saddle River, New Jersey: Prentice-Hall. Hornberger, L., Hight, T. and Walawalker, A. (2000), “Optimising the processing of recycled EPS foam,” Plastics in Building Construction, Vol. 21, No. 1, pp. 7-12. Horvath, J. S. (1994), “Expanded Polystyrene (EPS) – an introduction to material behaviour,” Geotextiles and Geomembranes, Vol. 13, No. 4, pp. 263 -280. Horvath, J. S. (1995), “Geofoam Geosynthetic: a monograph,” New York: Horvath Engineering. Horvath, J. S. (1996), “The compressible inclusion function of EPS geofoam,” Geotextiles and Geomembranes,” Vol. Houston, S. L., Houston, W. N. and Wayner, A. M. (1994), “Laboratory filter paper suction measurement,” Geotechnical Testing Journal, Vol.17, No.2, pp. 185-194. Hubble, G. D. (1972), “The swelling clay soils” in “physical aspects of swelling clay soils,” University of New England, Armidale. Ikada, H. (1990), “Problem of waste disposal and biodegradable plastic,” Tokyo: Agune Syofu co.

References

312

Imamura, S., Sueoka, T. and Kamon, M. (1996), “Long term stability of bentonite/sand mixtures at L.L.R.W. storage,” Environmental Geotechnics, M. Kamom (ed), Rotterdam: Balkema, pp. 545-550. Indraratna, B. (1992), “Problems related to disposal of fly ash and its utilisation as a structural fill,” Utilisation of waste materials in civil engineering construction, Inyang, H.I. and Bergson, K.L. (Eds.), ASCE, pp. 274-285. Ingold, T. S. and Miller, K. S. (1982), “Analytical and laboratory investigations of reinforced clay”, Proceedings of 2nd International Conference on Geotextiles, Lasvegas, Vol.3, pp. 587-592. Inyang, H. I. (2003), “Framework for recycling of wastes in construction,” Journal of Environmental Engineering, ASCE, Vol. 129, No. 10, pp. 887-898. Izgin, M. and Wasti, Y. (1998), “Geomembrane-sand interface frictional properties as determined by inclined board and shear box test,” Geotextiles and Geomembranes, Vol. 16, No. 4, pp. 207-219. Jayasekara, S. and Mohajerani, A. (2001), “An investigation of long-term effects of leachate on landfill clay liners,” Geoenvironment 2001, Environmental Geotechnics, Smith, Fityus & Allman (Eds.), New Castle: Australian Geomechanics Society Incorporated, pp. 359-364. Johnson, L. D. and Snethen, D. R. (1978), “Prediction of potential heave of swelling soil,” Geotechnical Testing Journal, ASTM, Vol.1, No. 3, pp. 117-124. Jones, D. E., and Jones, K. A. (1987), “Treating expansive soils,” Civil Engineering, ASCE, Vol. 57, No.8, pp. Jones, M., Thorley, C. and Boczek, E. (2001), “Analysis of soil types for use as mono-layer soil covers in landfills,” Geoenvironment 2001, Environmental Geotechnics, Smith, Fityus & Allman (Eds.), New Castle: Australian Geomechanics Society Incorporated, pp.379-384. Kalkan, E. and Akbulut, S. (2004), “The positive effects of silica fume on the permeability, swelling pressure and compressive strength of natural clay liners,” Engineering Geology, Vol. 73, pp. 145-156. Kamon, M., Katsumi, T., Sawa, N. and Ito, K. (2000), “Minimization of heavy metal leaching effect from dredged sediments involving reclamation”, Coastal geotechnical engineering in practice, Nakase and Tsuchida (Eds.), Rotterdam: Balkema, pp. 629-634. Kamon, M. and Katsumi, T. (2001), “Clay liners for waste landfill,” Clay science for engineering, Adachi & Fukue (Eds.), Rotterdam: Balkema, pp. 29-45. Kaniraj, S. R. and Gayathri, V. (2003), “Geotechnical behaviour of fly ash mixed with randomly oriented fiber inclusions,” Geotextiles and Geomembranes, Vol. 21, pp. 123-149.

References

313

Kaniraj, S. R. and Havanagi, V. G. (2001), “Behaviour of cement-stabilsed fiber-reinforced fly ash-soil mixtures,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 7, pp. 574-584. Katti, R.K. (1987), “Cohesion approach to mechanics of saturated expansive soil media,” Proc. of 6th International conference on expansive soils, New Delhi, India, Rotterdam: Balkema, pp. 536-578. Katti, R. K. and Katti, A. R. (1994), “Behaviour of saturated expansive soils and control methods,” Rotterdam: A.A. Balkema publishers. Katti, R. K., Humad, S., Dewakar, D. M., Kulkarni, S.K., Kahilkar, B. S., Chandrasekaran, V. S. and Sundaram, P. N. (1977), “Characteristics of Bombay marine clay in twin city area,” Geotechnical Aspects of Soft Clays, Brenner and Brand (Eds.), Bangkok: Asian Institute of Technology, pp. 27-43. Kayabali, K. (1997), “Engineering aspects of a novel landfill liner materials: bentonite-amended natural zeoloite,” Engineering Geology, Vol. 46, pp. 105-114. Kehew, A. E. (1995), “Geology for engineers and environmental scientists,” Prentice-Hall, Englewood cliffs, N.J. Kenny, T. C., Van Veen, W. A., Swallow, M. A. and Sungaila, M. A. (1992), “Hydraulic conductivity of compacted bentonite-sand mixtures,” Canadian Geotechnical Journal, Vol. 29, pp. 364-374. Kezdi, A. (1979), “Stabilised earth roads,” Developments in Geotechnical Engineering 19, Amsterdam: Elsevier Scientific publishing co. Khire, M. V., Benson, C. H. and Bosscher, P. J. (1997), “Water balance modelling of earthen final covers,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 123, No. 8, pp. 744-754. Kleppe, J. H. and Olson, R. E. (1985), “Desiccation cracking of soil barriers”, Johnson, A.I., Frobel, R.K., Cavalli, N.J., Petersson, C.B. (Eds.), Hydraulic Barriers in Soil and Rock, ASTM STP 874, ASTM, pp. 263-275. Kodikara, J. K. (2001), “Design of compacted clayey liners for waste containment,” Geoenvironment 2001, Environmental Geotechnics, Smith, Fityus & Allman (Eds.), New Castle: Australian Geomechanics Society Incorporated, pp. 321-333. Kodikara, J. K. (2006), “Conceptual approaches for considering shrinkage cracking in the cement stabilised pavement mix design”, 22nd ARRB Conference, Oct 29th to Nov 2nd 2006, Canberra, Australia, CD Rom Proceedings. Kodikara, J., Barbour, S. L. and Fredlund, D. G. (1999), “Changes in clay structure and behaviour due to wetting and drying,” Proceedings of 8th Australian-New Zealand conference on Geomechanics, Hobart, pp. 179-186.

References

314

Kodikara, J. K., Barbour, S. L. and Fredlund, D. G. (2000), “Desiccation cracking of soil layers”, Unsaturated soils for Asia, Rahardjo, Toll and Leong (Eds.), Rotterdam: Balkema, pp. 693-698. Kodikara, J.K., Rahman, F. and Barbour, S. L. (2002), “Towards a more rational approach to chemical compatibility testing of clay,” Canadian Geotechnical Journal, Vol. 39, No. 3, pp. 597-607. Koerner, R. M. and Daniel, D. E. (1997), “Final covers for solid waste landfills and abandoned dumps,” Virginia: ASCE press and co-published in London: Thomas Telford. Komine, H. and Ogata, N. (1999), “Experimental study on swelling characteristics of sand-bentonite mixtures for nuclear waste disposal,” Soils and Foundations, Vol. 39, No. 2, pp. 83-97. Kota, P. B. V. S., Hazlett, D. and Perrin, L. (1996), “Sulfate-bearing soils: Problems with calcium based stabilisers,” Transport Research Record, No.1546, pp. 62-69. Krahn, J. and Fredlund, D. G. (1972), “On total, matric and osmatic suction”, Soil Science, Vol.114, pp. 339-348. Krishnaswamy, N. R. and Raghavendra, H. B. (1989), “Behaviour of reinforced earth under direct shear test”, Proceedings of First Indian Geotextiles Conference on reinforced earth and Geotextiles, Rotterdam: Balkema, pp. C.47-C.52. Krishnaswamy, N. R. and Srinivasulu Reddy (1989), “Behaviour of reinforced earth under triaxial compression”, Proceedings of First Indian Geotextiles Conference on reinforced earth and Geotextiles, Rotterdam: Balkema, pp. A.41-A.46. Kumar, R., Kanaujia, V. K. and Chandra, D. (1999), “Engineering Behaviour of Fibre-Reinforced Pond Ash and Silty Sand,” Geosynthetics International, Vol. 6, No. 6, pp. 509-518. Lambe, P.C., Khosia, N.P. and Jayaratne, N.N. (1990), “Soil stabilization in pavement structures”, Report Project No. 23241-88-1, Centre for Transportation Engineering Studies, North Carolina state University, Raleigh, North Carolina. Lau, J. T. K. (1987), “Desiccation cracking of clay soils,” M.Sc. Thesis, University of Saskatchewan, Canada. Leong, E. C., He, L. and Rahardjo, H. (2002), “Factors affecting the filter paper method for total and matric suction measurements,” Geotechnical Testing Journal, ASTM, Vol. 25, No. 3, pp. 322-333. Li, C. (2005), “Mechanical response of Fiber-reinforced soil,” Ph. D. Dissertation, The University of Texas at Austin, U.S.A.

References

315

Li, T.D. and Zhao, Z.X. (1988), “Method of determining the shearing strength for cut slope in expansive soil,” Proceedings of the international conference on engineering problems of regional soils, Beijing, China, International Academic publishers, Pergamon press, pp. 606-609. Little, D. N. (1995), “Handbook for stabilisation of pavement subgrades and base courses with lime”, Dubuque, Iowa: Kendall/Hunt Publishing Company. Lister, N. W. and Powell, W. D. (1975), “The compaction of bituminous base and base course materials and its relation to pavement performance,” Proceedings of Association of Asphalt Pavement Technologists 1975, Vol. 44, pp. 75-107 Liu, T.H., Yan, X.K. and Peng, Y.H. (1988), “Field monitoring on an expansive soil slope during failure,” Proceedings of the international conference on engineering problems of regional soils, Beijing, China, International Academic publishers, Pergamon press, pp. 625-628. Loehr, J.E., Axtell, P.J. and Bowders. J. J. (2000), “Reduction of soil swell potential with fiber reinforcement,” GeoEng2000, International conference on Geotechnical & Geological Engineering, Melbourne, (CD-Rom), Look, B. G. (2005), “Equilibrium moisture content of volumetrically active clay earthworks in Queensland,” Australian Geomechanics, Vol. 40, No. 3, pp. 55-66. Low, P. F. (1992), “Interparticle forces in clay suspensions: Flocculation, viscous flow and swelling”, Proceedings of the 1989 Clay Mineral Society Workshop on the Rheology of Clay/Water Systems. Lye, S. W., Aw, H. S. and Lee, S. G. (2002), “Adhesives for bead fusion of recycled expandable polystyrene,” Journal of Applied Polymer Science, Vol. 86, pp. 456-462. Magnan, J. P. and Serrate, J. F. (1989), “Mechanical properties of expanded polystyrene for applications in road embankment,” Bull. Liaison LCPC, No 164, pp. 25-31. Mahalinga-Iyer, U and Williams, D. J. (1985), “Unsaturated shear strength behaviour of compacted lateritic soils,” Geotechnique, Vol. 45, No. 2, pp. 317-320. Maher, M. H. and Gary, D. (1990), “Static response of sands reinforced with randomly distributed fibers,” Journal of Geotechnical Engineering, ASCE, Vol. 116, No. 11, pp. 1661-1677. Maher, M. H. and Ho, Y. C. (1994), “Mechanical Properties of Kaolinite/ Fibre soil Composite,” Journal of Geotechnical Engineering, Vol. 120, No. 8, pp. 1381-1393.

References

316

Masia, M.J., Totoev, Y.Z. and Kleeman, P.W. (2004), “Modelling expansive soil movements beneath structures,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 6, pp. 572-579. McDonald, P. and Brown, R.G. (1993), “Ultra lightweight polystyrene for bridge approach fill,” Proceedings of 11th southeast Asian Geotechnical Conference, Singapore, pp. 664-668. McKeen, R. G. (1988), “Soil characterization using suction measurements”, New Mexico Engineering Research Institute, 25th Paving and Transportation Conference, University on New Mexico. McLaughlin, A. and Skahn, K. (2000), “EPA draft guidance on final landfill covers”, Proceedings of the 2000 EPA conference on phytoremediation: State of the science conference and other developments, Boston, MA. Accessed online on 31.03.2007 from http://www.epa.gov/ORD/NRMRL/Pubs/625R01011b/625R01011bchap28.pdf McManus, K. L., Nataraj, M. and Philips, G. M. (1993), “Long term evaluation and identification of the proper testing program for ASTM class F fly ash stabilised soils”, Louisiana Transportation Research centre Report. McQueen, I. S. and Miller, R. F. (1968), “Calibration and evaluation of wide range method of measuring moisture stress,” Journal of Soil Science, Vol. 106, No. 3, pp. 225-231. Miki, G. (1996), “Ten year history of EPS method in Japan and its future challenges,” Proceedings of International symposium on EPS construction Method, EPS TOKYO’96, Japan, pp. 394-411. Miki, H. (1996), “An overview of lightweight banking technology in Japan,” Proceedings of International Symposium on EPS Construction Method (EPS- Tokyo’96), 29-30 October, pp. 9-30. Miled, K., Roy, R. L., Sab, K. and Boulay, C. (2004), “Compressive behaviour of an idealised EPS lightweight concrete: Size effects and failure mode,” Mechanics of Materials, Vol. 36, pp.1031-1046. Miller, C. J., Mi, H. and Yesiller, N. (1998), “Experimental analysis of desiccation crack propagation in clay liners,” Journal of the American Water Resources Association, AWRA, Vol. 34, No. 3, pp. 677-686. Miller, C. J. and Rifai, S. (2004), “Fiber reinforcement for waste containment soil liners,” Journal of Environmental Engineering, ASCE, Vol. 130, No. 8, pp. 891-895. Millrath,K., Kozlova,S., Meyer,C. & Shimanovich,S. (2002), “New approach to treating the soft clay/silt fraction of dredged material”, Proceedings of the Third Specialty Conference on Dredging and Dredged Material Disposal – Dredging 02, Orlando, (full paper on CD-Rom),

References

317

Minegashi, K., Makiuchi, K. and Takahashi, R. (2002), “Strength-deformational characteristics of EPS beads-Mixed lightweight geomaterial subjected to cyclic loadings,” Proceedings of the international workshop on lightweight Geo-materials, Tokyo, Japan, pp. 119 – 125. Mitchell, J. K. and Soga, K. (2005), “Fundamentals of soils behaviour,” Third edition, New Jersey: John Wiley and Sons Inc. Miura, N., Bergado, D. T., Sakai, A. and Nakamura, R. (1987), “Improvements of soft marine clays by special admixtures using dry and wet jet mixing methods,” Proceedings of 9th Southeast Asian Geotechnical Conference, Bangkok, Thailand, pp. 8-35 to 8-46. Mohan, D. and Bhandari, R. K. (1977), “Analysis of Some Indian Marine Clays,” Geotechnical Aspects of Soft Clays, Brenner and Brand (Eds.), Bangkok: Asian Institute of Technology, pp. 59-74. Mollins, L. H., Stewart, D. I. and Cousens, T. W. (1996), “Predicting the properties of bentonite-sand mixtures,” Clay Minerals, Vol.31, pp. 243-252. Montgomery, R. J. and Parson, L. J. (1989), “The Omega Hill final cover test plot study; Three-year data summary,” Annual Meeting of the National Solid Waste Management Association, Washington, D. C. Montanez, J. E. C. (2002), “Suction and volume changes of compacted sand- bentonite mixtures,” Ph.D. Thesis, University of London. Mori, H. (2003), Personal communication, Research Engineer for EPS beads mixed lightweight soil, Public Works Research Institute, Japan. Mowafy, Y. W., Bauer, G. E. and Sakeb, F. H. (1985), “Treatment of expansive soils: A laboratory study,” Transportation Research Record, No. 1032, pp. 34-39. Muntohar, A. S. (2000), “Engineering behaviour of rice husk ash blended soil and its potential as road base construction,” Proceedings of GeoEng2000, Extended abstract (CD-Rom), Nalbantoglu, Z. and Gucbilmez, E. (2002), “Utilisation of an industrial waste in calcareous expansive clay stabilisation,” Geotechnical Testing Journal, Vol. 25, No.1, pp. 78-84. Negussey, D. (1998), “Putting polystyrene to work,” Civil Engineering, ASCE Vol. 68, No. 3, pp. 65-67. Nelson, J. D and Miller, D. J. (1992), “Expansive soils, problems and practice in foundation and pavement engineering,” John Wiley & Sons, Inc, USA. Nicholson, P.G., Kashyap, V. and Fujii, C. F. (1994), “Lime and fly ash admixture improvement of tropical Hawaiian soils,” Transportation Research Record, No 1440, pp. 71-78.

References

318

Nishimura, T. (2001), “Swelling pressure of a compacted bentonite subjected to high suction,” Clay Science for Engineering, Adachi & Fukue (Eds.), Rotterdam: Balkema, pp. 109-114. Noguchi, T., Inagaki, Y., Miyashita, M. and Watanable, H. (1998), “A new recycling system for expanded polystyrene using a natural solvent, part 2, development of a prototype production system,” Packaging Technology Science, Vol. 11, No.19, pp. 29-37. Ogino, T., Goto, T., Kataoka K and Kuroda, M. (1994), “Utilisation of stabilised dredged waste for construction materials,” Proceedings of the 1st ICGE, Edmonton, Canada, pp. 49-56. Oh, S. W., Lee, J. K., Kwon, Y. C. and Lee, B. J. (2002), “Bearing capacity of light weight soil using recycled Styrofoam beads,” Proceedings of the Twelfth International Offshore and Polar Engineering Conference, Kitakyushu, Japan, pp. 670-674. Okumura, T., Noda, S., Kitzawa, S. and Wada, K. (2000), “New ground material made of dredged soil for port and airport reclamation projects,” Nakase and Tsuchida (Eds.), Coastal geotechnical engineering in practice, Rotterdam: Balkema, pp. 697-702. Oren, A. H., Onal, O., Ozden, G. and Kaya, A. (2006), “Nondestructive evaluation of volumetric shrinkage of compacted mixtures using digital image analysis,” Engineering Geology, Vol. 85, pp. 239-250. Osinubi, K. J. and Nwaiwu, C. M. O. (2006), “Design of compacted lateritic soil liners and covers,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 132, No. 2, pp. 203-213. Osipov, V. I., Bik, N. N. and Rumjantseva, N. A. (1987), “Cyclic swelling of clays,” Applied Clay Science, Vol. 2, No. 7, pp. 363-374. O’Sullivan, C., Clarke, W. and Lockington, D. (2005), “Sources of hydrogen sulphide in ground water on reclaimed land”, Journal of Environmental Engineering, ASCE, Vol. 131, No. 3, pp. 471-477. Pandian, N. S., Nagaraj, T. S. and Raju, P. S. R. N. (1995), “Permeability and compressibility behaviour of bentonite- sand/ soil mixes,” Geotechnical Testing Journal, GTJODJ, Vol. 18, No. 1, pp. 86-93. Pandian, N. S. and Krishna, K. C. (2002), “California bearing ratio behaviour of cement-stabilised fly ash –soil mixes,” Journal of Testing and Evaluation, Vol. 30, No. 6, pp. 492-496. Pandian, N. S., Krishna, K. C. and Sridharan, A. (2001), “California bearing ratio behaviour of soil fly ash mixtures,” Journal of Testing and Evaluation, Vol. 29, No. 2, pp. 220-226.

References

319

Penman, H. L. (1963), “Vegetation and Hydrology, Technical Comment No. 53, Commonwealth Bureau of Soils, Harpenden, England. Petry, T.M. and Armstrong, J. C. (1989), “Stabilisation of expansive clay soils,” Transportation Research Record, No. 1219, pp. 103-112. Petry, T. M. and Little, D. N. (2002), “Review of stabilisation of clays and expansive soils in pavements and light loaded structures – History, Practice, and Future,” Journal of Materials in Civil Engineering, Vol. 14, No. 6, pp. 447-460. Perry, S. H., Bischoff, P. H. and Yamura, K. (1991), “Mix details and material behaviour of polystyrene aggregate concrete,” Magazine of Concrete Research, Vol. 43, pp. 71-77. PACIA, Plastics and Chemical Industries Association, (2005), “National plastics recycling survey (2004 calendar year) main survey report,” prepared by Nolan-ITU, Victoria, pp. 1-52. Popesco, M. (1980), “Behaviour of expansive soils with crumb structure,” 4th International Conference on Expansive Soils, Vol.1, ASCE, New York, pp. 158-171. Porbaha, A., Pradhan, T. B. S. and Yamane, N. (2000), “Time effect on shear strength and permeability of fly ash,” Journal of Energy Engineering, Vol. 126, No. 1, pp. 15-31. Port of Brisbane Corporation, (2001), Environmental reports – Port of Brisbane corporation sediment sampling and analysis programme of Brisbane River and Moreton bay. PPW Directive (2005), Directive 2005/20/E6 of the European Parliament and of the council of 9 March 2005 amending Directive 94/62/EC on Packaging and Packaging Waste (OJ L 70 of 2005.03.16) Prabakar, J and Sridhar, R. S. (2002), “Effect of random inclusion of sisal fibre on strength behaviour of soil,” Construction and Building Materials, Vol. 16, pp. 123-131. Pradhan, T. B. S., Hirano, Y., Tanabe, T. and Natori, H. (1995), “Stabilised light soil using vinylide chloride foam,” Proceedings of European conference on soil mechanics and foundation engineering II, Copenhagen, Vol. 2, pp. s2.121-s2.126. Pradhan, T.B.S., Imai, G., Hamano, M and Nagasaka ,Y, (1993), “Failure criterion of a light geotechnical material SLS,” Proceedings of Third International offshore and Polar Engineering Conference, Singapore, 6-11 June. Preber, T., Bang, S., Chung, Y. and Cho. Y. (1994), “Behaviour of expanded polystyrene blocks,” Transportation Research Record, No. 1462, pp. 36-46.

References

320

Punthutaecha, K. (2002), “Volume change behaviour of expansive soils modified with recycled materials,” Ph.D. Thesis, The university of Texas at Arlington. Punthutaecha, K., Puppala, A. J., Vanapalli, S. K. and Inyang, H. (2006), “Volume change behaviours of expansive soils stabilised with recycled ashes and fibers,” Journal of Materials in Civil Engineering, ASCE, Vol. 18, No. 2, pp. 295-306. Puppala, A. J., Mohammad, L. N. and Allen, A. (1996), “Engineering behaviour of lime-treated Louisiana subgrade soil,” Transportation Research Record, No. 1546, pp. 24-31. Puppala, A. J., Katha, B. and Hoyos, L. R. (2004), “Volumetric shrinkage strain measurements in expansive soils using digital imaging technology,” Geotechnical Testing Journal, Vol. 27, No. 6, pp. 547-556. Puppala, A., Hoyos, L., Viyanant, C. and Musenda, C. (2000), “Fiber and fly ash stabilisation methods to treat soft expansive soils,” Proceedings of soft ground technology conference, ASCE press, pp. 136 – 145. Puppala, A. J. and Musenda, C. (2000), “Effects of fiber reinforcement on strength and volume change in expansive clay,” Transportation Research Record, No. 1736, pp. 134-140. Puppala, A. J., Wattanasanticharoen, E. and Hoyos, R. (2003), “Ranking of four chemical and mechanical stabilisation methods to treat low-volume road subgrades in Texas,” Transportation Research Record, No.1819, pp. 63-71. Qian, X., Koerner, R. M. and Gray, D. H. (2002), “Geotechnical aspects of landfill design and construction,” New Jersey: Prentice Hall. Rajasekaran, G. and Rao, S. N. (1998), “Particle size analysis of lime treated marine clay,” Geotechnical Testing Journal, ASTM, Vol. 21, No. 2, pp. 109-119. Ranjan, G., Vasan, R. M. and Charan, H. D. (1996), “Probabilistic analysis of randomly distributed fibre-reinforced soil,” Journal of Geotechnical Engineering, ASCE, Vol. 122, No. 6, pp. 49-426. Rankin, G. and Fairweather, S. (1978), “Expansive soil clays,” Seminar on foundations in expansive clay soils, Resource materials centre, DDIAE, Darling Downs, pp. 2-4. Rao, N. S. and Kodandaramaswamy, K. (1981), “The prediction of settlements and heave in clays,” Canadian Geotechnical Journal, Vol. 17, pp. 623-631. Rao, S. M., Reddy, B. V. V. and Muttharam, M. (2001), “Effect of cyclic wetting and drying on the index properties of a lime-stabilised expansive soil,” Ground Improvement, Vol. 5, No. 3, pp.107-110.

References

321

Rao, S. M., Reddy, B. V. V. and Muttharam, M. (2001), “The impact of cyclic wetting and drying on the swelling behaviour of stabilised expansive soils,” Engineering Geology, Vol. 60, pp. 223-233. Ravindrarajah, R. S. and Tuck, A.J. (1994), “Properties of expanded concrete containing treated expanded polystyrene beads,” Cement and Concrete Composites, Vol. 1, No. 6, pp. 73-77. Rauch, A. F., Harmon, J. S., Katz, L. E. and Liljestrand, H. M. (2002), “Measured effects of liquid soil stabilisers on engineering properties of clay,” Transportation Research Record, No. 1787, pp. 33 – 41. Reed, R. F. and Kelly, M. (1995), “Application of soil suction in Dallas/Fort Worth,” Soil suction applications in geotechnical engineering practice, Wray, W.K. and Houston, S.L. (Eds.), New York: ASCE press, pp. 58 – 67. Refsdal, G. (1987), “Future trends for EPS use,” Plastic foam in road embankments, Norwegian Road Research Laboratory Report No. 61, pp. 17-20. Reneker, D. H. and Chun, I. (1996), “Nanometre diameter fibres of polymer produced by electrospinning”, Nanotechnology, Vol. 7, pp. 216-223. Richards, B. G. (1990), “Footings for small and domestic structures,” Linn Education and Training Services, Brisbane. Ricou, P., Lecuyer, I. and Le Cloirec, P. (1999), “Removal of Cu2+, Zn2+, Pb2+ by adsorption onto fly ash and fly ash/lime mixing,” Water Science and Technology, Vol. 39, No. 10, pp. 239-247. Ridley, A. M. (1993), “The measurement of soil moisture suction,” Ph. D. Thesis, University of London. Ritchie, J. T. (1972), “Model for predicting evaporation from a row crop with incomplete cover,” Water Resources Research, Vol. 8, No. 5, pp. 1204-1212. Rodatz, W. and Oltmanns, W. (1997), “Permeability and stress-strain behaviour of fibre-reinforced soils for landfill liner systems”, Advanced landfill liner systems, August, H., Holzlohner and Meggyes, T. (Eds.), London: Thomas Telford, pp. 321-332. Rogers, C. D. F and Lee, S. J. (1994), “Drained shear strength of lime-clay mixes,” Transportation Research Record, No. 1440, pp. 53-62. Rowe, R. K. (2001), “Barrier systems,” In geotechnical and geoenvironmental engineering handbook (ed. R.K. Rowe), Boston: Kluwer Academic. Sahu, B. K. (2001), “Improvement in California bearing ratio of various soils in Botswana by fly ash,” International ash utilisation symposium, University of Kentucky, paper #90, http://www.flyash.info.

References

322

Sarsby, R. (2000), “Environmental Geotechnics”, London: Thomas Telford. Satoh, T., Tsuchida, T., Mitsukuri, K. and Hong, Z. (2001), “Field placing test of lightweight treated soil under seawater in Kumamoto port,” Soils and Foundations, Vol. 41, No. 5, pp. 145-154. Scheirs, J. (1998), “Polymer Recycling – Science, Technology and Applications,” Wiley series in polymer science, John Wiley & Sons Ltd, England. Schroeder, P., Lloyd, C. and Zappi, P. (1994), “The Hydrologic Evaluation of Landfill Performance (HELP) Model User’s Guide for Version 3.0., U.S. Environmental Protection Agency, EPS/600/R-94/168a, Cincinnati, OH. Seed, H. B., Woodward, R. J. and Lundgren, R. (1964), “Fundamental aspects of Atterberg limits” Journal of soil mechanics and foundation engineering division, ASCE, Vol. 90, No. SM6, pp. 75-105. Setty, K. R. N. S. and Murthy, A. T. A. (1990), “Behaviour of fibre-reinforced black cotton soil,” Proceedings of Indian Geotechnical Conference, Bombay, pp. 45-49. Setty, K. R. N. S. and Rao, S. V. G. (1987), “Characteristics of fibre reinforced lateritic soil,” Proceedings of Indian Geotechnical Conference, Bangalore, Vol.1, pp. 329-333. Sherwood, P. (2001), “Alternate materials in road construction, a guide to the use of recycled and secondary aggregates,” London: Thomas Telford Publishing, Second edition. Shin, C. and Chase, G. G. (2005), “Nanofibers from recycle waste expanded polystyrene using natural solvent,” Polymer Bulletin, Vol. 55, pp. 209-215. Shin, C. (2005), “A new recycling method for expanded polystyrene,” Packaging Technology and Science, Vol.18, pp. 331-335. Shirazi, S. M., Kazama, H. and Oshinbe, M. (2005), “Permeability of bentonite and bentonite-sand mixtures,” Australian Geomechanics, Vol. 40, No. 4, pp. 27-36. Sibley, J. W. and Williams, D. J. (1990), “A new filter material for measuring soil suction,” Geotechnical Testing Journal, Vol. 13, No. 4, pp. 381-384. Siderius, R. M. (1998), “Feasibility of EPS as a lightweight sub-base material in railway structures”, Report No. 7-98-211-8, Delft University of Technology, Delft. Sivapullaiah, P. V., Sridharan, A. and Stalin, V. K. (1996), “Swelling behaviour of soil-bentonite mixture,” Canadian Geotechnical Journal, Vol. 33, pp. 808-814.

References

323

Sivapulliah, P. V. and Sridharan, A. (1985), “Liquid limit of soil mixtures,” Geotechnical Testing Journal, ASTM, Vol. 8, No. 3, pp. 111-116. Skinner, H . D. (2000), “Building on unsaturated fills: Compaction, suction and volume change,” Unsaturated soils for Asia, Rahardjo, Toll & Leong (eds), Rotterdam: Balkema, pp. 613-618. Snethen, D. R. and Huang, G. (1992), “Evaluation of soil suction – heave prediction methods,” Proceedings of 7th International Conference on Expansive soils, Dallas, Texas, pp. 12-17 Sorochan, E. A. (1991), “Construction of buildings on expansive soils”, Rotterdam/Brookfield: Balkema. Sridharan, A. and Gurtug, Y. (2004), “Swelling behaviour of compacted fine-grained soils,” Engineering Geology, Vol. 72, pp 9-18. Sridharan, A., Nagaraj, H. B. and Prakash, K. (1999), “Determination of the plasticity index from flow index,” Geotechnical Testing Journal, ASTM, Vol. 22, No. 2, pp. 169-175. Sridharan, A. and Nagaraj, H. B. (2005), “Plastic limit and compaction characteristics of fine grained soils”, Ground Improvement, Vol. 9, No. 1, pp. 17-22. Sridharan, A., Sreepada Rao, A. and Sivapullaiah, P. V. (1986), “Swelling pressure of clays,” Geotechnical Testing Journal, ASTM, Vol. 9, No. 1, pp. 24- 33. Stepkowska, E.T. (1987), “Physical properties of expansive soils related to particle thickness”, Proceedings of 6th International conference on expansive soils, ISSMFE, New Delhi, India, Vol. 2, pp. 583-590. Subba Rao, K. S. and Satyadas, G. G. (1987), “Swelling potential with cycles of swelling and partial shrinkage,” 6th International Conference on Expansive soils, Vol. 1, New Delhi, India, pp.137-142. Tatlisoz, N., Benson, C. and Edil, T. (1997), “ Effect of fines on mechanical properties of soil-tire chip mixtures,” Testing soil mixed with waste or recycled materials, ASTM STP 1275, Mark A.Wasemiller, Keith B. Hoddinott, Eds., American society for testing and materials. Tay, Y. Y., Stewart, D. I. and Cousens, T. W. (2001), “Shrinkage and desiccation cracking in bentonite-sand landfill liners”, Engineering Geology, Vol. 60, pp. 263-274. Thompsett, D. J., Walker, A., Radley, R. J. and Grieveson, B .M. (1995), “Design and construction of expanded polystyrene embankments - Practical design methods as used in the United Kingdom,” Construction and Building Materials, Vol. 9, No. 6, pp. 403-411.

References

324

Thomson, M. R. (1970), “Suggested method of mixture design for lime-treated soils”, Special Technical Publication No.479, Special procedures for testing soil and rock for engineering purposes, ASTM, Philadelphia. Thompson, R. W. and McKeen, R. G. (1995), “Heave prediction using soil suction – a case history,” Soil suction applications in geotechnical engineering practice, Wray, W.K. and Houston, S.L. (Eds.), New York: ASCE press, pp. 1-13. Thomson, D. A. (1995), “Polystyrene recycling: an overview of the industry in North America,” In plastics, Rubber, and paper recycling, a pragmatic approach, ACS symposium series 609, Rader, C. P., Baldwin, S. D., Cornell, D.D., Sadler, G. D. and Stockel, R.F. (Eds.), Washington: American Chemical Society, pp. 89-96. Thorley, C. B. and Boczek, E. J. (2000), “Design and monitoring of landfill cover systems,” Proceedings of GeoEng 2000, CD Rom. Tigchelaar, J, De Feijter, J.W. and Den Hann E.J. (2000), “Shear tests on reconstituted Oostvaardersplassen clay,” Proceedings of Soft Ground Technology Conference, ASCE press, pp. 67 – 81. Tremblay, H., Leroueil, S. and Locat, J. (1998), “Stabilisation of clayey soils from Eastern Canada at high water contents,” Proceedings of the 3rd International Congress on Environmental Geotechnics, Lisbon, Portugal, pp. 337-340. Tripathy, S., Subba Rao, K. S. and Fredlund, D. G. (2002), “Water content – void ratio swell-shrink paths of compacted expansive soils”, Canadian Geotechnical Journal, Vol. 39, pp. 938-959. Tsuchida, T., Takeuchi, D., Okumura, T. and Kishida, T. (1996), “Development of light-weight fill from dredgings,” Environmental Geotechnics, Kamon (Ed.), Rotterdam: Balkema, pp. 415-420. Tsuchida, T., Porbaha, A. and Yamane, N. (2001), “Development of a geomaterial from dredged bay mud,” Journal of Materials in Civil Engineering, Vol. 13, No. 2, pp. 152-160. Tsuchida, T and Kang, M. S. (2003), “Case studies of lightweight treated soil method in seaport and airport construction project,” 12th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, Leung et al (Eds.), World scientific publishing, pp. 249-252. US Environmental Protection Agency, (1989), Final covers on hazardous waste landfill and surface impoundments, EPA530-SW-89-047. US Environmental Protection Agency (1993), “Quality assurance and quality control for waste containment facilities”, Technical Guidance Document, EPS/600/R-93/182. Usmen, M. A. and Bowders, J. J. Jr., (1990), “Stabilisation characteristics of class F fly ash,” Transport Research Record, No. 1288, pp. 59-60.

References

325

Van Ree, C. C. D. F., Weststrate, F. A., Meskers, C. G. and Bremer, C. N. (1992), “Design aspects and permeability testing of natural clay and sand-bentonite liners,” Geotechnique, Vol. 42, No. 1, pp. 49-56. Venakatarama Reddy, B. V. and Jagadish, K. S. (1993), “The static compaction of soils,” Geotechnique, Vol. 43, No. 2, pp. 337-341. Vogel, H. -J., Hoffmann, H. and Roth, K. (2005), “Studies of crack dynamics in clay soil, I. Experimental methods, results, and morphological quantification”, Geoderma, Vol. 125, pp. 203-211. Wallace, K. (1988), “Low cost roads on cracking clay soils, a review; with particular reference to Queensland conditions,” School of Civil Engineering, Queensland University of Technology. Wasti, Y. and Ozduzgun, Z. B. (2001), “Geomembrane-geotextile interface shear properties as determined by inclined board and direct shear box test,” Geotextiles and Geomembranes, Vol.19, No. 1, pp. 45-57. Whitlow, R. (2000), “Basic soil mechanics”, Harlow, England; New York: Prentice Hall. Wibawa, B. and Rahardjo, H. (2001), “Stabilisation of a compacted swelling clayey soil,” Clay Science for Engineering, Adachi & Fukue (Eds.), Rotterdam: Balkema, pp. 125-130. Wilding, L. P. and Tessier, D. (1988), “Genesis of Vertisols, shrink swell phenomena,” Vertisols: Their Distribution, Properties, Classification and Management, Wilding and Puentes (Eds.), Texas A&M University Printing Centre, pp. 55-81. Wiley III, J. B., Tharwani, R. M. and Morgan, L. P. (2002), “Beneficial use of dredged material in Brownfield”, Proceedings of the Third Specialty Conference on Dredging and Dredged Material Disposal – Dredging 02, Orlando (full paper on CD-Rom) Williams, A. A. B. and Donaldson, G. W. (1980), “Developments relating to building on expansive soils in South Africa: 1973 -1980”, Proceedings of the 4th International Conference on Expansive Soils, Denver, Vol. 2, pp. 834-838. Williams, D. and Snowden, R. A. (1990), “A47 great Yarmouth western bypass: performance during the first three years,” Transport and Road Research Laboratory Contractor Report No. 211. Winterkorn, H. F. and Pamukcu, S. (1991), “Soil stabilisation and grouting,” Foundation Engineering Handbook (2nd Edition), New York: Van Nostrand Reinhold, pp. 317-378. Wykeham Farrance (1995), “Material testing equipment,” 14th edition, Wykeham Farrance Eng. Ltd., Slough, England.

References

326

Yamane, N., Taguchi, H., Kishida, T. and Porbaha, A. (2000), “Application of FL-CPL for project control in the coastal areas,” Nakase and Tsuchida (Eds.), Coastal Geotechnical Engineering in Practice, Rotterdam: Balkema, pp. 697-702. Yasufuku, N., Ochiai, H., Omine, K. and Suetsugu, D. (2002), “Geotechnical reuse of waste expanded polystyrene as a light weight geomaterial,” Environmental Geotechnics (4th ICEG), Demello & Almedia (Eds.), Lisse: Swets & Zeitlinger, pp. 603-608. Yesiller, N., Miller, C. J., Inci, G. and Yaldo, K. (2000), “Desiccation and cracking behaviour of three compacted landfill liner soils,” Engineering Geology, Vol. 57, pp.105-121. Yetimoglu, T. and Salbas, O. (2003), “A study on shear strength of sands reinforced with randomly distributed discrete fibres,” Geotextiles and Geomembranes, Vol. 21, pp. 103-110. Yevnin, A. and Zaslavsky, D. Z. (1970), “Some factors affecting compacted clay swelling,” Canadian Geotechnical Journal, Vol. 7, No.1, pp 79-89. Yoonz, G. L., Jeon, S. S. and Kim, B. T. (2004), “Mechanical characteristics of light-weighted soils using dredged materials,” Marine Georesources and Geotechnology, Vol. 22, pp. 215-229. Zaline, N. and Emin, G. (2002), “Utilisation of an industrial waste in calcareous expansive clay stabilisation,” Geotechnical Testing Journal, Vol. 25, No.1, pp 78-84. Ziegler, S., Leshchinsky, D., Ling, H. I. and Perry, E. B. (1998), “Effect of short polymeric fibers on crack development in clays,” Soils and Foundations, Vol. 38, No. 1, pp. 247-253. Zou, Y. (2001), “Behaviour of the expanded polystyrene (EPS) geofoam on soft soil,” Ph. D. Thesis, The University of Western Sydney, Nepean.

Appendix

327

328

Dry unit weight

Dry unit weight, kN/m3

EPS, % SB16 SB24 SB32

0.0 16.97 17.06 16.77

0.3 15.89 15.79 15.79

0.6 14.61 14.22 14.22

0.9 13.24 12.55 12.26 Free swell

Free swell, %


0.0 29.07 50.01 71.94

0.3 22.67 48.54 64.93

0.6 18.94 44.64 56.93

0.9 11.87 34.84 43.10 Swell pressure

Swell pressure, kPa


0.0 58.98 100.73 126.31

0.3 40.96 77.39 118.55

0.6 29.39 51.71 80.72

0.9 22.00 33.73 53.47

329

Volumetric shrinkage

Volumetric shrinkage, %


0.0 15.51 21.45 32.13

0.3 13.07 19.65 25.02

0.6 9.93 16.16 21.16

0.9 7.73 14.32 16.43 Axial shrinkage, %

Axial shrinkage, %


0.0 5.02 8.90 11.59

0.3 3.91 7.29 7.04

0.6 2.89 4.35 5.87

0.9 1.74 3.04 3.47 Diametral shrinkage, %

Diametral shrinkage, %


0.0 5.68 7.14 12.38

0.3 4.88 6.90 10.19

0.6 3.69 6.38 7.62

0.9 3.09 6.00 6.95

330

Direct shear stress

Cohesion, kPa


0.0 6.70 40.42 62.2

0.3 21.04 40.94 47.75

0.6 27.90 33.6 44.75

0.9 35.48 36.19 38.25

Angle of internal friction, °


0.0 36.94 42.06 46.27

0.3 34.95 36.72 44.38

0.6 34.55 34.79 39.50

0.9 35.05 33.95 38.00 Unconsolidated – Undrained triaxial tests

Cohesion, kPa


0.0 46.82 72.87 81.13

0.3 45.77 64.55 74.66

0.6 40.00 48.02 64.75

0.9 35.25 32.95 63.90

Angle of internal friction, °


0.0 34.40 30.83 26.47

0.3 30.22 27.58 25.86

0.6 26.27 26.91 23.51

0.9 23.17 25.42 16.86

331

Desiccation studies

(150 mm diameter, 20 mm high samples) CIF, %


0.0 10.34 14.94 22.26

0.3 8.73 13.97 19.03

0.6 7.61 12.74 17.44

0.9 4.91 12.16 14.53



0.0 11.16 15.24 19.34

0.3 8.02 13.49 18.93

0.6 6.50 11.92 15.53

0.9 5.88 10.97 15.74



0.0 8.81 15.10 19.86

0.3 6.92 12.73 16.89

0.6 6.55 12.38 14.21

0.9 5.00 9.97 12.31



0.0 9.06 14.69 21.58

0.3 7.29 11.88 18.58

0.6 4.43 11.58 16.77

0.9 4.00 10.00 13.95

332



0.0 9.88 15.98 20.00

0.3 7.69 15.27 17.81

0.6 6.75 11.58 14.79

0.9 4.56 10.00 12.00

333

Matlab program Matlab® image processing program used for extracting the Crack Intensity Factor (CIF)in desiccation studies. Function Image_Processing(picture_no) % Reading Input File tue = num2str(picture_no) tue1 = '.jpg' tue2 = [ tur tue1 ]; f = imread(tue2); imshow(f); I = rgb2gray(f); % Converts to Black and White Image threshold = graythresh(I); bw = im2bw(I,threshold); imshow(bw) % Detects Centre of the Image bw = bwareaopen(bw,30); se = strel('disk',2); bw = imclose(bw,se); bw = imfill(bw,'holes'); imshow(bw) c = [43 185 212]; r = [38 68 181]; BW2 = bwselect(bw,c,r,4); imview(bw), imview(BW2) % Counts Number of Pixel outside of the Central Image tec = 0; for i = 1:480 for j = 1:640 if (BW2(i,j)==0) tec = tec + 1; end; end; end; tec BW2 = ~BW2; imshow(BW2) % Superimposing of the images to Eliminate Unwanted Portions of the Image figi=imoverlay(f,BW2,[1 1 1]); imshow(figi) figi1 = im2bw(figi); imshow(figi1) tec1 = 0; for i = 1:480

334

for j = 1:640 if (figi1(i,j)==0) tec1 = tec1 + 1; end; end; end; % Calculates the Percentage of Crack Area crc = 0; crc = ((tec1)/((640*480)-tec))*100; 342 341 341

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