Post on 20-Jun-2018
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
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To my parents,
(late) Illuri Harinatha Babu Rao and
Illuri Hymavathy.
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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: ___________________________________
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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.
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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
5.9 Compaction curve for SB24 105
5.10 Compaction curve for SB32 105
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
6.3 Compaction curves for SB24 at different EPS contents 118
6.4 Compaction curves for SB32 at different EPS contents 118
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
7.3 Variation of free swell with time at different EPS contents for SB24 136
7.4 Variation of free swell with time at different EPS contents for SB32 137
7.5 Time-Free swell hyperbolic relationship for SB16 139
7.6 Free swell vs. time for SB16 at 0.0% EPS content 140
7.7 Free swell vs. time for SB16 at 0.3% EPS content 140
7.8 Free swell vs. time for SB16 at 0.6% EPS content 140
7.9 Free swell vs. time for SB16 at 0.9% EPS content 140
7.10 Free swell vs. time for SB24 at 0.0% EPS content 141
7.11 Free swell vs. time for SB24 at 0.3% EPS content 141
7.12 Free swell vs. time for SB24 at 0.6% EPS content 141
7.13 Free swell vs. time for SB24 at 0.9% EPS content 141
7.14 Free swell vs. time for SB32 at 0.0% EPS content 142
7.15 Free swell vs. time for SB32 at 0.3% EPS content 142
7.16 Free swell vs. time for SB32 at 0.6% EPS content 142
7.17 Free swell vs. time for SB32 at 0.9% EPS content 142
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
7.22 Variation of free swell with clay content for 0.3% EPS 146
7.23 Variation of free swell with clay content for 0.6% EPS 146
7.24 Variation of free swell with clay content for 0.9% 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
7.32 Reduction in swell pressure, free swell and dry unit weight for SB24 152
7.33 Reduction in swell pressure, free swell and dry unit weight for SB32 152
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
8.4 Variation of primary settlement with bentonite content at
0.3% EPS content 182
8.5 Variation of primary settlement with bentonite content at
0.6% EPS content 182
8.6 Variation of primary settlement with bentonite content at
0.9% 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
8.8 Direct shear results for SB16 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 185
8.9 Direct shear results for SB16 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 186
8.10 Direct shear results for SB24 at 25 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 186
8.11 Direct shear results for SB24 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 187
8.12 Direct shear results for SB24 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 187
8.13 Direct shear results for SB32 at 25 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 188
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Figure Title Page
8.14 Direct shear results for SB32 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 188
8.15 Direct shear results for SB32 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
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
8.18 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 192
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 193
8.20 Variation of shear stress with normal stress for SB16 194
8.21 Variation of shear stress with normal stress for SB24 195
8.22 Variation of shear stress with normal stress for SB32 195
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
8.28 Stress - strain curves at different EPS contents for SB24 at confining
pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 204
8.29 Stress - strain curves at different EPS contents for SB32 at confining
pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 205
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
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 207
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Figure Title Page
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 208
8.33 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB16 210
8.34 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB24 210
8.35 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB32 211
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
8.38 Composite modulus for SB24 at confining pressures of (a) 25 kPa
(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 214
8.39 Composite modulus for SB32 at confining pressures of (a) 25 kPa
(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 215
8.40 The relation between measured and predicted initial tangent Young’s
modulus 216
8.41 s-t plots for SB16 217
8.42 s-t plots for SB24 218
8.43 s-t plots for SB32 218
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
5.8 Optimum lime content for SB24 mix 108
5.9 Optimum lime content for SB32 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
8.5 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB24 209
8.6 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB32 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
9.3 Relationship between suction and shear stress for SB24 245
9.4 Relationship between suction and shear stress for SB32 246
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)
xxx
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).
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).
Chapter 2
16
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.
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.
Chapter 2
21
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.
Chapter 2
22
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
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.
Chapter 2
25
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.
Chapter 2
28
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.
Chapter 2
29
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.
Chapter 2
30
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).
Chapter 2
32
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
33
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
Chapter 3
43
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
Chapter 3
44
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
Chapter 3
45
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
Chapter 3
46
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.
Chapter 3
47
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
Chapter 3
48
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
Chapter 3
49
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.
Chapter 3
50
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
Chapter 3
51
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
Chapter 3
52
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.
Chapter 3
53
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
Chapter 3
54
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
Chapter 3
55
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.
Chapter 3
56
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
Chapter 3
57
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.
Chapter 3
58
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).
Chapter 3
59
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).
Chapter 3
60
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.
Chapter 3
61
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.
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.
Moisture Content = 39%
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
Moisture Content = 45%
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.
Moisture Content = 50%
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
45% moisture content
50% 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
with 2% EPSwithout EPS
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
with 2% EPSwithout EPS
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
soil 116 Northeast of Turkey
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,
soil 416 Northeast of Turkey
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,
soil 316 Northeast of Turkey
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).
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,
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).
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
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
Figure 5.9 Compaction curve for SB24.
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
Figure 5.10 Compaction curve for SB32.
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
Moulding moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 6.3 Compaction curves for SB24 at different EPS contents.
SB32
0.3% EPS
0.6% EPS
0.9% EPS
0.0% EPS
10
12
14
16
18
5 10 15 20 25
Moulding moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 6.4 Compaction curves for SB32 at different EPS contents.
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
Figure 7.3 Variation of free swell with time at different EPS contents for SB24.
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
Figure 7.4 Variation of free swell with time at different EPS contents for SB32.
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, %
Experimental dataHyperbolic fit
Figure 7.8 Free swell vs. time for SB16 at 0.6% EPS content. Figure 7.9 Free swell vs. time for SB16 at 0.9% EPS content.
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, %
Experimental dataHyperbolic fit
Figure 7.14 Free swell vs. time for SB32 at 0.0% EPS content. Figure 7.15 Free swell vs. time for SB32 at 0.3% EPS content.
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
Figure 7.16 Free swell vs. time for SB32 at 0.6% EPS content. Figure 7.17 Free swell vs. time for SB32 at 0.9% EPS content.
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%).
The experimental data was quantitatively analysed by multiple regression models
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, %,
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 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, %
0.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
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
Bentonite content, %
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%).
The experimental data was quantitatively analysed by multiple regression models
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,
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 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
0.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
Figure 7.29 Relation between the PI and the measured and predicted values of
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
Maximum swell pressure
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
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 7.33 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
Bentonite content, %
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
The experimental data was quantitatively analysed by multiple regression models
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, %,
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 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
15 20 25 30 35 40 45 50 55Plasticity Index, %
Vol
um
etric
shr
inka
ge, %
0.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
Figure 7.47 Relation between the PI and the measured and predicted values of
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).
8.1.1 Test procedure
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
10 15 20 25 30 35Bentonite content, %
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
10 15 20 25 30 35Bentonite content, %
Set
tlem
ent,
mm
Figure 8.4 Variation of primary settlement with bentonite content at 0.3% EPS content.
0.6% EPS
25 kPa
50 kPa
100 kPa
0
1
2
3
10 15 20 25 30 35Bentonite content, %
Set
tlem
ent,
mm
Figure 8.5 Variation of primary settlement with bentonite content at 0.6% EPS content.
0.9% EPS
25 kPa
50 kPa
100 kPa
0
1
2
3
10 15 20 25 30 35Bentonite content, %
Set
tlem
ent,
mm
Figure 8.6 Variation of primary settlement with bentonite content at 0.9% EPS content.
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
0 2 4 6 8Shear displacement, mm
She
ar s
tres
s, k
Pa
0.0% EPS, 50 kPa0.3% EPS, 50 kPa0.6% EPS, 50 kPa0.9% EPS, 50 kPa
(a) (a)
SB16
-0.20
0.20.40.60.8
11.21.41.61.8
0 2 4 6 8Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
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
Shear displacement, mm
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
Shear displacement, mm
Ver
tical
di
spla
cem
ent,
mm
0.0% EPS, 25kPa0.3% EPS, 25 kPa0.6% EPS, 25kPa0.9% EPS, 25 kPa
(b) (b)
Figure 8.9 Direct shear results for SB16 at 100 kPa normal stress, Figure 8.10 Direct shear results for SB24 at 25 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
187
SB24
0
20
40
60
80
100
0 1 2 3 4 5 6 7Shear displacement, mm
She
ar s
tres
s, k
Pa
0.0% EPS, 50 kPa0.3% EPS, 50 kPa0.6% EPS, 50 kPa0.9% EPS, 50 kPa
SB24
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6 7Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
Ver
tical
di
spla
cem
ent,
mm
0.0% EPS, 100 kPa0.3% EPS, 100 kPa0.6% EPS, 100 kPa0.9% EPS, 100 kPa
5 (b) 6 (b)
Figure 8.11 Direct shear results for SB24 at 50 kPa normal stress, Figure 8.12 Direct shear results for SB24 at 100 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
188
SB32
0102030405060708090
100
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, 25kPa0.9% EPS, 25 kPa
SB320
20
40
60
80
100
120
0 2 4 6 8Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
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
Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
She
ar s
tres
s, k
Pa
SB16SB24SB 32
(b)
0.3% EPS, 100 kPa
020406080
100120140160180
0 2 4 6 8Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
She
ar s
tres
s, k
Pa
SB16SB24SB32
(a)
0.6% EPS, 50 kPa
0
20
40
60
80
100
0 1 2 3 4 5 6 7Shear displacement, mm
She
ar s
tres
s, k
Pa
SB16SB24SB32
(b)
0.6% EPS, 100 kPa
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6 7Shear displacement, mm
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
0 2 4 6 8Shear displacement, mm
Sh
ear
stre
ss, k
Pa
SB16SB24SB32
(a)
0.9% EPS, 50 kPa
0
10
20
30
40
50
60
70
80
90
0 2 4 6 8Shear displacement, mm
She
ar s
tres
s, k
Pa
SB16SB24SB32
(b)
0.9% EPS, 100 kPa
0
20
40
60
80
100
120
140
0 2 4 6 8Shear displacement, mm
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
Figure 8.21 Variation of shear stress with normal stress for SB24.
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
Figure 8.22 Variation of shear stress with normal stress for SB32.
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
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
(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
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
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
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
(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
0 5 10 15 20Axial strain, %
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
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
(c) (d)
Figure 8.28 Stress - strain curves at different EPS contents for SB24 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
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
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
SB32, 50 kPa
0
50
100
150
200
250
300
350
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
(a) (b)
SB32, 100kPa
0
100
200
300
400
500
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
SB32, 200kPa
0
100
200
300
400
500
600
700
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS0.3% EPS0.6% EPS0.9% EPSLine of peaks
(c) (d)
Figure 8.29 Stress - strain curves at different EPS contents for SB32 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
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
0 5 10 15 20Axial strain, %
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
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25 kPa 50 kPa100 kPa 200 kPaLine of peaks
(a) (b)
SB24, 0.6% EPS
0
100
200
300
400
500
600
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25 kPa 50 kPa100 kPa 200 kPaLine of peaks
SB24, 0.9% EPS
0
100
200
300
400
500
0 5 10 15 20 25Axial strain, %
Dev
aito
r st
ress
, kP
a
25 kPa 50 kPa100 kPa 200 kPaLine of peaks
(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
0 5 10 15 20Axial strain, %
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
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25kPa 50 kPa100 kPa 200 kPaLine of peaks
(a) (b)
SB32, 0.6% EPS
0
100
200
300
400
500
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25kPa 50 kPa100 kPa 200 kPaLine of peaks
SB32, 0.9% EPS
0
50
100
150
200
250
300
350
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25 kPa 50 kPa100 kPa 200 kPaLine of peaks
(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
Table 8.5 Deviator stress ( ) f31 σσ − and strain ( fε ) at failure for SB24
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
Table 8.6 Deviator stress ( ) f31 σσ − and strain ( fε ) at failure for SB32
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
Figure 8.34 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB24.
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
Figure 8.35 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB32.
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
SB16, 50 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
(a) (b)
SB16, 100 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
SB16, 200 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
(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
SB24, 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
SB24, 50 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
(a) (b)
SB24, 100 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
SB24, 200 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
(c) (d)
Figure 8.38 Calculated composite modulus for SB24 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
Chapter 8
215
SB32, 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
SB32, 50 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
(a) (b)
SB32, 100 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
SB32, 200 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
(c) (d)
Figure 8.39 Calculated composite modulus for SB32 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
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
Figure 8.42 s-t plots for SB24.
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
Figure 8.43 s-t plots for SB32.
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
15 20 25 30 35 40 45 50 55Plasticity Index, %
Coh
esio
n, k
Pa
0.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
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%).
The experimental data was quantitatively analysed by multiple regression models
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, °
PI is plasticity index, %
EPS is quantity of EPS, %
These equations are 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 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
0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks
(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
0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks
(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
SB24, 0.3% EPS, with lime
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
50 kPa100 kPa200 kPaLine of peaks
(a) (b)
SB24, 0.6% EPS, with lime
0
200
400
600
800
1000
1200
0 2 4 6 8 10 12Axial strain, %
Dev
iato
r st
ress
, kP
a
50 kPa100 kPa200 kPaLine of peaks
SB24, 0.9% EPS, with lime
0
100
200
300
400
500
600
700
0 2 4 6 8 10 12 14Axial strain, %
Dev
iato
r st
ress
,kP
a
50 kPa100 kPa200 kPaLine of peaks
(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
Table 9.3 Relationship between suction and shear stress for SB24 (Moulding
moisture content = 12.0%).
Peak deviator stress at confining stress, kPa EPS,
%
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
Table 9.4 Relationship between suction and shear stress for SB32 (Moulding
moisture content = 14.0%).
Peak deviator stress at confining stress, kPa EPS,
%
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)
86 mm dia, 40 mm high
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
150 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)
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)
150 mm dia, 70 mm high
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
, %
20 mm high35 mm high70 mm high
(b)
SB32, 150 mm dia
11
13
15
17
19
21
23
0 0.2 0.4 0.6 0.8 1EPS, %
CIF
, %
20 mm high35 mm high70 mm high
(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
150 mm dia, 70 mm high
86 mm dia, 40 mm high
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
150 mm dia, 70 mm high
86 mm dia, 40 mm high
8
10
12
14
16
18
0 0.2 0.4 0.6 0.8 1EPS, %
CIF
, %
(b)
SB32, H/D = 0.47
150 mm dia, 70 mm high
86 mm dia, 40 mm high
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
86 mm dia, 20 mm high
0
2
4
6
8
10
12
0 0.2 0.4 0.6 0.8 1EPS, %
CIF
, %
(a)
SB24, H/D = 0.23150 mm dia, 35 mm high
86 mm dia, 20 mm high
0
3
6
9
12
15
18
0 0.2 0.4 0.6 0.8 1EPS, %
CIF
, %
(b)
SB32, H/D = 0.23150 mm dia, 35 mm high
86 mm dia, 20 mm high
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).
10.1.1 Test procedure
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.
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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.
10.2.1 Test procedure
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).
Chapter 10
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.
Chapter 10
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).
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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
Chapter 10
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
Average head on top of layer 2
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.
0.0% EPS 0.3% EPS 0.6% EPS Parameter mm mm mm
Precipitation 572.33 572.23 572.33 Runoff 18.09 15.36 5.60 Evaporation 542.99 535.61 501.26 Percolation/ Leakage through layer 2
11.25 21.15 65.46
Average head on top of layer 2
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.
0.0% EPS 0.3% EPS 0.6% EPS Parameter mm mm mm
Precipitation 269.29 269.29 269.29 Runoff 5.08 4.92 4.38 Evaporation 252.69 247.02 235.32 Percolation/ Leakage through layer 2
11.64 17.31 29.55
Average head on top of layer 2
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.
Chapter 10
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.
Chapter 11
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
Chapter 11
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.
Chapter 11
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
Chapter 11
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
Chapter 11
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.
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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
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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
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Appendix
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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, %
EPS, % SB16 SB24 SB32
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
EPS, % SB16 SB24 SB32
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
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Volumetric shrinkage
Volumetric shrinkage, %
EPS, % SB16 SB24 SB32
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, %
EPS, % SB16 SB24 SB32
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, %
EPS, % SB16 SB24 SB32
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
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Direct shear stress
Cohesion, kPa
EPS, % SB16 SB24 SB32
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, °
EPS, % SB16 SB24 SB32
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
EPS, % SB16 SB24 SB32
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, °
EPS, % SB16 SB24 SB32
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
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Desiccation studies
(150 mm diameter, 20 mm high samples) CIF, %
EPS, % SB16 SB24 SB32
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
(150 mm diameter, 35 mm high samples) CIF, %
EPS, % SB16 SB24 SB32
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
(150 mm diameter, 70 mm high samples) CIF, %
EPS, % SB16 SB24 SB32
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
(86 mm diameter, 20 mm high samples) CIF, %
EPS, % SB16 SB24 SB32
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
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(86 mm diameter, 40 mm high samples) CIF, %
EPS, % SB16 SB24 SB32
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
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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