POST CYCLIC BEHAVIOUR OF MALAYSIAN PEAT SOIL

HABIB MUSA BIN MOHAMAD

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

ii

POST CYCLIC BEHAVIOUR OF MALAYSIAN PEAT SOIL

HABIB MUSA BIN MOHAMAD

A thesis submitted in

fulfillment of the requirement for the award of the

Degree of Master of Civil Engineering

Faculty of Civil and Environmental Engineering

Universiti Tun Hussein Onn Malaysia

SEPTEMBER 2015

iv

Dedicated to my beloved parents, family and friends.

Mohamad Bin Habib Ali @ Bacho

Nor Jamilah Binti Abdul Kadir

Tabanac Château

Larkin Residence

For their love, endless support, encouragement & sacrifices.

v

ACKNOWLEDGEMENT

In the name of Allah, the Most Gracious and the Most Merciful Alhamdulillah, all

praises to Allah for the strengths and His blessing in completing this thesis. I would

like to take this opportunity to express my heartfelt gratitude to all those who helped

me to make my thesis work a success.

First and foremost, I have to thank my parents for their love and support

throughout my life. I’m forever indebted to my family who, understanding the

importance of this study to me, you will always be in my heart where absence makes

the heart grow fonder. Special appreciation goes to my supervisor, Assoc. Prof. Dr.

Adnan Bin Zainorabidin (Director of Centre of Alumni Advancement and Relations,

Universiti Tun Husein Onn Malaysia) for his support, guidance and cooperation. His

invaluable help of advices and suggestions throughout the experimental and thesis

works have contributed to the success of this research. Like proverbial, you can’t

make bricks without straws. A bouquet of thanks to the RECESS members, Mrs.

Salina Binti Sani, Mr. Amir Zaki Bin Salikin and Mr. Mudzaffar Syah Bin Kamarudin,

dear colleagues and friends for the helps, experiences and cooperation. I express my

heart full thanks to all staffs in the Faculty of Civil and Environmental Engineering for

their helps and who had involved directly or indirectly contributed in this research,

your kindness means a lot to me. Last but not least, deeply from my heart with love

and faith, I would like to thank my sweet siblings and love, in Tabanac Château and

Larkin Residence for their outstanding and highly appreciated patience day and night

throughout the time of my study, May Allah blessed them all for ever. May Allah

grant us Jannat Al Firdausi.

vi

ABSTRACT

In Malaysia, there are 2.4 million hectares of land covered by peat soil, with 1.5 million

hectares available in Sarawak alone. The conversion and draining of peatland for construction,

infrastructure, housing and industrial projects has created several maintenance issues that are

increasingly appearing on the peat soil. The conventional method that was used to design the

roads only considers soil shear strength through static load and does not take into account the

vehicular dynamic loading and shear strength thereafter. The purpose of this research is to

investigate the engineering properties of peat soils and evaluate the effects of peat soil

behaviour under static and dynamic loading. This is also to evaluate and establish the post-

cyclic undrained behaviour while comparing it to static monotonic stress-strain behaviour.

This research is focused on the post-cyclic shear strength of peat soil behaviour characteristics

based on cyclic loading and shear strength curves derived from triaxial test under consolidated

undrained conditions. Static and post-cyclic monotonic load tests were carried out on peat

soil samples from Parit Nipah, Johor (PNpt) and Penor, Pahang (PRpt). 175 specimens were

tested, and prepared under effective stresses at 13kPa, 25kPa, 50 kPa, 100 kPa and 200 kPa.

Whereas, dynamic load tests were carried out in different frequencies to simulate the loading

type such as vibration of machineries, wind, traffic load and earthquake in field from 0.5 Hz,

1.0 Hz, 1.5 Hz and 2.0 Hz with 100 numbers of loading cycles. Post-cyclic monotonic shear

strength results as compared to static test showed some significant changes in reduction of

stress-strain behaviour. Post-cyclic shear strength decreases with the increase in the

frequencies. Averagely, the PRpt has dominantly higher in reduction strength in post-cyclic

at 59.24% while PNpt is approximately about 58.72%. Prior to critical yield strain level, the

peat specimen experience a significant deformation. The deformation of peats triggers

changes in soil structures that causes reduction in stress-strain behaviour. Thus, it can be

concluded that the stress-strain behaviour of peat soil decreased after 100 numbers of cyclic

loading in post-cyclic test as compared to the static tests, and it decreased substantially when

frequencies were applied.

vii

ABSTRAK

Terdapat 2.4 juta hektar tanah gambut di Malaysia, dengan 1.5 juta hektar sahaja terdapat di

Sarawak. Penukaran dan penyaliran tanah gambut untuk pembinaan, infrastruktur, perumahan

dan projek-projek perindustrian menyebabkan isu penyelenggaraan selepas pembinaan

semakin ketara pada tanah gambut. Kaedah konvensional telah digunakan dalam mereka

bentuk jalan raya dengan mempertimbangkan kekuatan ricih tanah melalui beban statik dan

tidak mengambil kira beban dinamik daripada kenderaan selepas itu. Tujuan kajian ini adalah

untuk menyiasat sifat-sifat kejuruteraan pada tanah gambut dan menilai kesan kelakuan tanah

gambut di bawah pembebanan statik dan dinamik. Ini juga adalah untuk menilai dan

menerbitkan tingkah laku tak tersalir selepas kitaran berbanding kelakuan tegasan-terikan

semasa ujian statik. Kajian ini memberi tumpuan kepada kekuatan ricih selepas getaran pada

tanah gambut dan ciri tingkah laku berdasarkan beban getaran dan lengkung kekuatan ricih

yang diperolehi daripada ujian tiga paksi di bawah keadaan tak tersalir disatukan. Ujian beban

statik dan selepas getaran dijalankan ke atas sampel tanah gambut dari Parit Nipah, Johor

(PNpt) dan Penor, Pahang (PRpt). 175 sampel telah diuji, dan berada di bawah tekanan

tegasan berkesan pada 13kPa, 25kPa, 50 kPa, 100 kPa dan 200 kPa. Manakala, ujian beban

dinamik yang dijalankan pada frekuensi yang berbeza untuk mensimulasikan jenis bebanan

seperti getaran jentera, angin, beban trafik dan gempa bumi di tapak daripada 0.5 Hz, 1.0 Hz,

1.5 Hz dan 2.0 Hz dengan 100 kali beban getaran. Selepas getaran, keputusan kekuatan ricih

telah dibandingkan dengan ujian statik dan terdapat beberapa perubahan penting dalam

pengurangan kelakuan tegasan-terikan. Kekuatan ricih selepas getaran berkurangan dengan

peningkatan frekuensi. Secara purata, PRpt adalah lebih dominan kearah kekuatan yang lebih

tinggi dan pengurangan slepas getaran adalah pada kadar 59.24% manakala PNpt adalah pada

kadar 58.72%. Sebelum tahap ketegangan kritikal dihasilkan, specimen tanah gambut telah

mengalami perubahan bentuk yang ketara. Perubahan bentuk tanah gambut bermaksud

perubahan dalam struktur tanah yang menyebabkan pengurangan dalam tingkah laku tegasan-

terikan. Oleh itu, dapat disimpulkan bahawa kelakuan tegasan-terikan tanah gambut menurun

selepas 100 kali beban getaran selepas berlku getaran berbanding dengan ujian statik dan

menurun dengan ketara mengikut frekuensi digunakan.

viii

TABLE OF CONTENT

TITLE ii

DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENTS v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF TABLE xii

LIST OF FIGURE xiv

LIST OF SYMBOL AND ABBREVIATION xviii

LIST OF APPENDICES xix

CHAPTER 1: INTRODUCTION

1.1 Background of study 1

1.2 Problem statement 4

1.3 Objective of study 4

1.4 Scope of study 5

1.5 Significant of Study 6

CHAPTER 2: LITERATURE REVIEW

2.1 Introduction 7

2.2 Peat soil 8

2.3 Peat content and formation 9

2.4 Peat Area in Malaysia 10

2.5 Classification of Peat Soil 11

ix

2.6 Engineering Properties of Peat 14

2.7 Shear Strength of Peat Soil 22

2.7.1 Undrained Shear Strength 23

2.8 Static Test 24

2.8.1 Consolidated Undrained Triaxial Test 26

2.8.2 Static Testing Program 30

2.9 Dynamic Loading Test 35

2.10 Post-Cyclic Shear Strength of Peat Soil 41

2.11 Review of Post Cyclic Response on Peat Soil 44

2.12 Post-Cyclic Undrained Monotonic Behaviour 50

2.13 Post-Cyclic Normalized Undrained Shear Strength 51

2.14 Research Drives 52

CHAPTER 3: METHODOLOGY

3.1 Introduction 53

3.2 Research methodology 54

3.3 Site Location 55

3.4 Site Conditions during Sampling 57

3.4.1 Parit Nipah, Batu Pahat, Johor 56

3.4.2 Penor, Pekan, Pahang 59

3.5 Sampling Method 60

3.5.1 Disturbed Sampling Method 60

3.5.2 Undisturbed Sampling Method 61

3.6 Index Properties 64

3.6.1 Particle Size Distribution 66

3.6.2 Degree of Humification 67

3.6.3 Specific Gravity 68

3.6.4 Moisture content 70

3.6.5 Organic Content 71

3.6.6 Liquid Limit 73

3.6.7 Fibre Content 74

3.6.8 pH test 75

3.7 Standard Procedure for Triaxial Checking Transducers

Calibration 76

x

3.7.1 Calibration of Cell Pressure 77

3.8 Static Test 78

3.8.1 Monotonic Triaxial Test 78

3.8.2 Specimen Preparation 79

3.8.3 Saturation Stage 82

3.8.4 Consolidation Stage 82

3.9 Shearing Stage 83

3.10 Dynamic Stage 84

3.10.1 Cyclic Triaxial Test 85

3.11 Post-Cyclic Shear Test 87

3.12 ELDYN Software Test Procedure 87

3.12.1 Saturation Stage 88

3.12.2 Consolidation Stage 90

3.12.3 Shearing Stage 91

3.12.4 Cyclic Stage 92

3.12.5 Post-Cyclic Shear Stage 94

3.13 Data Encapsulation and Analysis 96

CHAPTER 4: DATA ANALYSIS AND DISCUSSION

4.1 Introduction 94

4.2 Index Properties Test 95

4.2.1 Degree of Humification Test 95

4.2.2 Particle Size Distribution Test 96

4.2.3 Specific Gravity Test 98

4.2.4 Liquid Limit Test 98

4.2.5 Moisture Content Test 99

4.2.6 Organic Content Test 100

4.2.7 Fibre Content Test 101

4.2.8 pH Test 101

4.3 Summary of Index Properties 102

4.4 Monotonic Triaxial Test 104

4.4.1 Repeatability of Test 104

4.4.2 Static monotonic test 106

4.5 Cyclic Triaxial Test 114

xi

4.5.1 Cyclic Triaxial Behaviour Analysis 114

4.5.2 Pore Water Pressure Behaviour 115

4.6 Post-Cyclic Behaviour of Peat 121

4.7 Effect of Cyclic Strain 121

4.7.1 Stress-Strain Behaviour 122

4.7.2 Excess Pore Water Pressure 132

4.8 Undrained Post-Cyclic Monotonic Behaviour 139

4.8.1 Shear Stress 139

4.9 Variation of Post-Cyclic Normalized 145

4.9.1 Normalized Undrained Shear Strength 145

4.9.2 Normalized Excess Pore Water Pressure 149

4.10 Triaxial Test Mode of Failure 154

4.11 Chapter Summary 155

CHAPTER 5: CONCLUSIONS AND RECOMMENDATION

5.1 Introduction 159

5.2 Conclusion 160

Objective 1 - The Physical Properties of Peat Soil in Parit Nipah,

Johor and Penor, Pahang. 161

Objective 2 – Peat Soils Behaviour under Static and

Cyclic Loading. 163

Objective 3 - Establishment of Post-Cyclic Behaviour

of Peat Soil. 165

Objective 4 - Static and Post-Cyclic Monotonic

Stress-Strain Behaviour 167

5.3 Recommendation for Further Investigation 169

REFERENCE 170

APPENDICES 171

xii

LIST OF TABLE

1.0 Status of peat soil areas in Malaysia. 2

2.1 Descriptions of Peat 8

2.2 The estimated extent of peat cover in Malaysia 11

2.3 Characteristic of peat swamps in Malaysia 12

2.4 The Von Post Scale for Assessing Peat

Decomposition 13

2.5 Tabulated of Peat Soil Properties in Malaysia 17

2.6 Summary of Laboratory Tests 19

2.7 Summary of Definition and Significant Index

Properties Tests 20

2.8 Principal characteristics of the examined peat 29

2.9 Amplitude values in monotonic triaxial test 32

2.10 Dynamic Parameter from Past Researcher 40

2.11 Typical test frequency ranges for cyclic triaxial testing 40

2.12 The definition of post-cyclic study from

various researcher 42

2.13 Tabulated of Post-cyclic Past Researcher 49

3.1 Specimen labelled in symbol of peat

based on Location 56

3.2 Summary of Laboratory Tests 74

3.3 Schedule of Calibration Triaxial Apparatus 76

3.4 Calibration of Cell Pressure 77

3.5 Cyclic Properties and Number of Sample 86

3.6 Components Function of ELDYN System 86

3.7 Target Required for Amplitude and Datum Values 94

4.1 Von Post Degree of Humification 95

4.2 Result of Particle Size Distribution Test 97

xiii

4.3 Specific Gravity Test Results 98

4.4 Percentage of Moisture Content 100

4.5 Percentage of Organic Content 100

4.6 Percentage of Fibre Content 101

4.7 pH value of Tested Peat 102

4.8 Tabulated of Peat Soil Properties in Malaysia 103

4.9 Datum and Amplitude Values for Cyclic Loading 108

4.10 Tabulated of Maximum Deviator Stress

from Various Researchers 109

4.11 Shear Strength Properties Changes in

Post-Cyclic for PNpt 131

4.12 Shear Strength Properties Changes in

Post-Cyclic for PRpt 131

xiv

LIST OF FIGURE

1.1 Malaysia peat soil distribution map. 3

2.1 Peat subsidence at the eastern edge of South East

Pahang Peat Swamp Forest at the transition from

undisturbed forest to degraded peatland. 10

2.2 Profile morphology of drained organic soils 14

2.3 Relationship between Shear Strength,

Moisture Content and Degree of Humification 23

2.4 Results of Undrained Triaxial Shear Strength Test on 28

Undisturbed Peat Sample.

2.5 Triaxial test on peat specimen reinterpreted to determine 32

the shear strength of Penor peat, Pahang.

2.6 Pore pressure vs. axial strain for the undrained test. 34

2.7 Triaxial Test Mode Of Failure 34

2.8 Cyclic loading conditions in the laboratory to simulate 36

level ground and sloping ground conditions

2.9 Stress-versus-strain relationship for Vicksburg

silty clay under sustained and axial pulsating stress 37

2.10 Cyclic triaxial test at 100th number of cycles 38

2.11 Cyclic triaxial test results at 10 seconds 39

2.12 Datum setup for cyclic triaxial test 45

2.13 The influenced of cyclic loading to the shear

strength for PRpt. 45

2.14 Effect of cyclic loading on post-cyclic

behaviour of specimen 47

2.15 Undrained monotonic shear stress and pore water pressure 50

xv

2.16 Post-Cyclic Normalized Undrained Shear Strength

versus Sand Content 51

3.1 Methodology Flowchart 53

3.2 Field Location of Peat Sampling in Peninsular Malaysia. 56

3.3 Research on Peat Soil Station (REPEATS) Parit Nipah 57

3.4 Parit Nipah Site Location Encircled with Plantations 58

3.5 Road Deterioration in Parit Nipah 58

3.6 Access Road to Penor, Pekan, Pahang, Malaysia 59

3.7 Penor, Sampling Site in Bush Areas 59

3.8 Tube Sampler Planted 61

3.9 Illustration of the tube sampler setup condition 62

3.10 Tube sampler in vertical position and penetrate to the soil 62

3.11 (a) Sample waxed both ends and sealed (b) Sample storage 63

3.12 Sizes of Sieve Apertures 67

3.13 Representative Sample of Peat Squeezed 68

3.14 Specific Gravity Equipment 69

3.15 Kerosene and Peat Specimens Mixed in Pyconometre 69

3.16 Peat Specimens for Moisture Content Test 71

3.17 Loss of Ignition Peat Specimens 72

3.18 Cone Penetrometer Equipment 73

3.19 Cone Penetration Test Supported Equipment 74

3.20 Dispersing Agent and Reagent for Fibre Content Test 74

3.21 Electrometric pH meter set 76

3.22 GDS Enterprise Level Dynamic

Triaxial Testing System (ELDYN) 80

3.23 Monotonic Triaxial Test Tools 81

3.24 Monotonic Triaxial Test Tools 81

3.25 GDS Enterprise Level Dynamic Triaxial

Testing System (ELDYN) 85

3.26 Screen-shot for Saturation Ramp Setup – Stage 1 88

xvi

3.27 Screen-shot for Saturation Ramp Setup – Stage 2 89

3.28 Screen-shot for B-Check Setup – Stage 3 89

3.29 Screen-shot for Consolidation Setup – Stage 4 90

3.30 Screen-shot for Shearing Consolidated

Undrained Setup – Stage 5 91

3.31 Screen-shot for Shearing – Axial Strain Setup – Stage 5 92

3.32 Screen-shot for Cyclic Loading Setup – Stage 6 92

3.33 Screen-shot for Cyclic Loading Setup – Stage 6 93

3.34 Screen-shot for Post-Cyclic Shear Setup – Stage 7 95

3.35 Screen-shot for Post-Cyclic Shear Axial

Strain Setup – Stage 7 95

4.1 Particle Size Distribution Graph 96

4.2 Penetration Graph for PNpt and PRpt 99

4.3 Repeatability of Static Testing 105

4.4 Stress-Strain Relationships at Different Effective

Stress, ’ for PNpt 107

4.5 Stress-Strain Relationships at Different Effective

Stress, ’ for PRpt 107

4.6 Pore Water Pressure of PNpt 110

4.7 Pore Water Pressure of PRpt 110

4.8 Stress-Strain Results Comparison with Various Researchers 112

4.9 Excess Pore Water Pressure Results

Comparison with Various Researchers 113

4.10 Relationships Pore Pressure Ratio, ru and

Number of Cycles for PNpt At frequencies 116

4.11 Relationships Pore Pressure Ratio, ru and

Number of Cycles for PRpt At frequencies 119

4.12 Relationships Pore Pressure Ratio, ru and

Number of Cycles with Past Researcher 120

xvii

4.13 Relationships Deviator Stress, q and Axial Strain,

a for PNpt 124

4.14 Relationships Deviator Stress, q and

Axial Strain, a for PRpt 130

4.15 Relationships Excess Pore Pressure, u and

Axial Strain, a for PNpt 135

4.16 Relationships Excess Pore Pressure, u and

Axial Strain, a for PRpt 138

4.17 Relationships Shear Stress, and Shear Strain,

for PNpt with 141

4.18 Relationships Shear Stress, and Shear Strain,

for PRpt with 144

4.19 Normalized Undrained Shear Strength for PNpt

versus Frequencies. 147

4.20 Normalized Undrained Shear Strength for PRpt

versus Frequencies. 148

4.21 Normalized Excess Pore Water Pressure for PNpt

versus Frequencies. 152

4.22 Normalized Excess Pore Water Pressure for PRpt

versus Frequencies. 153

4.23 Failure Condition of Peat Soil 154

4.24 Failure Envelope for Static Test 156

4.25 Failure Envelope for Post-Cyclic 157

xviii

LIST OF SYMBOL AND ABBREVIATION

PRpt - Penor peat

PNpt - Parit Nipah peat

POpt - Pontian peat

∆σ′ - Effective pressure

CTX - Cyclic triaxial

Cu - undrained shear strength

N - Number of cyclic

CIU - consolidated isotropic undrained

CU - Consolidated Undrained

q - Deviator stress

u - Pore pressure

a - Axial strain

Gs - Specific Gravity

LL - Liquid Limit

PL - Plastic Limit

rur - Pore Pressure Ratio

Su - Normalized Undrained Shear Strength

umax - Maximum excess pore water pressures

p’ - Mean effective stress

UTHM - Universiti Tun Hussein Onn Malaysia

RECESS – Research Center for Soft Soil Malaysia

xix

LIST OF APPENDIX

APPENDIX TITLE PAGE

A Influence of Cyclic Loading to the Shear 180

Strength of Peat Soil

B Comparison Study of the Dynamic Characteristics 181

Between Peat and Sand

C Post-Cyclic Behaviour of Soil – A Critical Review 182

D The Characteristics of Pontian Peat under 183

Dynamic Loading

E Pre- and Post-Cyclic Behaviour on Monotonic Shear 184

Strength of Penor Peat

F Post-cyclic Shear Strength Behaviour of Peat Soil 185

G Effect of Cyclic Loading on Post-Cyclic Behaviour of 186

Peat Soil in Consolidated Undrained Triaxial

1

CHAPTER 1

INTRODUCTION

1.1 Background of Study

Malaysia, comprising the regions of Peninsular, Sabah and Sarawak, supports some

of the most extensive tropical peatlands in the world. Tropical peat forest is found

mainly in Southeast Asia (Phillips, 1998) it was estimated at about 20 million

hectares, two-third of the total area of the world’s tropical peat swamps (Kyuma,

1992). In Peninsular Malaysia, they are found in the coastal areas of the east and

west coast, especially in the coastal areas of west Johore, Kuantan and Pekan district,

the Rompin-Endau area, northwest Selangor and the Trans-Perak areas in the Perak

Tengah and Hilir Perak district as shown in Figure 1.1. In Sarawak, peat occurs

mainly between the lower stretches of the main river course (basin peat) and in

poorly drained interior valleys (valley peats). They are found in the administrative

division of Kuching, Samarahan, Sri Aman, Sibu, Sarikei, Bintulu, Miri, and

Limbang. In Sabah, the organic soils are found on the coastal areas of the Klias

peninsula, Krah swamps in Kota Belud, Sugut and Labuk centuries and

Kinabatangan floodplains. The peat swamp forest is well represented in Borneo

(Phillips, 1998). The Klias Peninsular contained the largest pieces of peat swamp

forest at the northern end of Borneo.

2

Figure 1.1 Malaysia peat soil distribution map.

(Wetlands International – Malaysia. March 2010)

However, Peat is in the category of problematic soil because it has low shear

strength and high compressibility, which are not suitable for construction (Said and

Taib, 2009). Peat soil is not suitable for the construction of embankment, highway,

building or any other load bearing engineering structures due to the fact that it is

having extreme low shear strength and bearing capacity. In natural state, peat

consists of water and decomposed plant fragment with virtually no measurable

strength (Munro, 2004).

Therefore, it is essential to find an alternative to improve the strength since

nowadays lands are very expensive and very limited. Peat soil is not only soft, it is

compressible to where this characteristic will lead to excessive settlement which is a

very serious problem. Generally, peat soil is considered as a soft soil as it has high

settlement value even under moderate loading condition.

Sabah

Sarawak

3

Peat swamps cover about 2.7 million hectares in Malaysia. Nearly 63% of this

area or about 1.7 million hectares are in the East Malaysian state of Sarawak

according to Shenbaga and Huong (2009). Construction of road networks and other

infrastructural facilities on the peat land fairly difficult and the maintenance issue

after construction often rise up as major topic. Table 1.1 shows the proportionate

distribution status of peat soil areas in Malaysia. Values in parentheses are the

percentage proportion of total peat soil area and the data for peat swamp forest from

the year 2000 (Wong, 2003). The total for moderately and severely disturbed peat

land comprise Wong’s classes of medium and low density peat swamp forest.

Table 1.0: Status of peat soil areas in Malaysia.

(Wetlands International – Malaysia. March 2010)

Regions Total

peat soil

area (ha)

Undisturbed/

relatively

undisturbed (ha)

Moderately

Disturbed (ha)

Peat

soils

under

infrastructure (ha)

Peninsular Malaysia 642, 857 226, 026 (35) 66, 353 15, 512

Sabah 116, 965 21, 000 (18) 27, 757 17, 767

Sarawak 1, 697, 847 223, 277 (13) 488, 357 nd

Total 2, 457, 730 470, 303 (19) 582, 528 33, 633 (1)

*nd - not defined

Construction on peat soil will experience significant short-term and long-term

settlement with regard to stability and long-term settlements. In road design as an

example, conventional method used where the vehicular traffic on the roadway,

treated as static loads and the vehicular dynamic loading and shear strength thereafter

that related to the earthquake, rail transit or vibrating machinery that called

post-cyclic are not considered. Thus, Erken and Ulker (2008) has stated that, in

laboratory investigation, the post-cyclic monotonic shear strengths were evaluated

using various numbers of cycles of dynamic loading. This thesis has examined and

discuss the characterisation of the peat soil that has a significant effect to the

post-cyclic behaviour as well as the shear strength of peat soil. The response of soil

to cyclic loading are induced significant to the shear strength for a more practical

design parameter to be considered.

4

1.2 Problem Statement

Peat is known as a one of the most problematic soil in the construction industry.

Construction on peat soils has proven to be a challenging task to civil engineers since

this soil type has a very low bearing capacity and the settlement is high. Conversion

and draining of peatland for construction, infrastructure, housing and industrial

projects are occurring at an alarming technology to solve the maintenance issue after

construction that increase significantly. The peat layers itself in the subsoil lead to

irregular subsidence of roads, railways and foundations. In settlement analysis, it is

often that the long term compressibility parameters of peat is underestimated or

neglected. This situation can lead to problem regarding on the structure stability in

the future. For many years, in road design as an example, conventional method was

applied in designed the road by considering soil shear strength through static load

and do not take into account the vehicular dynamic loading and shear strength

thereafter. Shafiee et al., (2013) in prior study was investigated volume change

characteristics of peats associated with cyclic loading. The researcher has stated that,

the pore pressure generates during cyclic loading relatively low and undergoing

cyclic softening and induced strength lost but not has been formally investigated.

This research carried out to investigate the post-cyclic behaviour of peat soil and

changes in shear strength accordingly.

The characteristics of peat soil are high organic content, high water content,

large void ratio and high compressibility naturally influence the impact of uneven

settlement of subgrade on the surfaces of flexible pavements and often results in a

damage to buildings and engineering structures. In practice, the design engineer

more focus on shear strength based on static load. In this study, researcher stressed

on post-cyclic shear strength. The frequencies used in this research is simulation to

the dynamic loading and pulse frequency from 0.5Hz, 1.0Hz, 1.5Hz and 2.0Hz are

represented from traffic loading and up to the earthquake level to ensure that the

results of simulation are applicable to the real application. The knowledge of the

shear strength for post-cyclic behaviour of peat soil is essential as it enables

designers to understand the response of the soil when loaded and presentable

suggestion for proper engineering solutions to overcome the problem.

5

1.3 Objective of Study

Based on the study to examine the soil properties and identify the effect of post-

cyclic loading exerts a key role in tropical peat soil stability. The following

objectives therefore set out for this research.

a) To investigate the physical properties of peat soil.

b) To evaluate the effect of peat soil behaviour under static and cyclic

loading.

c) To establish the post-cyclic behaviour of peat soil.

d) To analyse static monotonic and post-cyclic monotonic stress-strain

behaviour.

1.4 Scope of Study

The aim of this study is to investigate the behaviour of peat soil under static and

dynamic loading. This research focused on the characteristic of peat soil samples

from Penor, Pahang (PRpt) and Parit Nipah (PNpt) Johor. The testing and evaluation

test for peat soil sample are conducted by using GDS Enterprise Level Dynamic

Triaxial Testing System (ELDYN) apparatus and load applied from top in

compliance to BS 1377-8: 1990. Laboratory tests for the peat soil are conducted in

Research Center for Soft Soil Malaysia (RECESS), Universiti Tun Hussein Onn

Malaysia (UTHM) Batu Pahat, Johor. This experimental research limits its scope on

the shear strength of peat soil that obtained from pre-cyclic test and post-cyclic test

in consolidated undrained condition. The frequencies of test are performed variously

at 0.5Hz, 1.0Hz, 1.5Hz and 2.0Hz. This research discovered the post-cyclic stress-

strain behaviour of peat soil.

6

1.5 Significant of Study.

This research is undertaken in academic study with a view to improve the designing

technique and emphasizing parameters in general. By its nature, it is expected that

policies of research will contribute to the development of the national construction

and technology industries for well developing project quality and enhancement of

design system. Design method and parameters consideration in order to produce

better product quality and applicable on site as well, the load design itself should be

derived in proper understanding to ensure the achievable idea in sustainability in

quality of construction method. At the end of this research, researcher expected to

share the factual correlation of undrained shear strength behaviour to improve and

refined so that the designing process and post construction issue can be minimised.

This research certainly gives an impact to the research to overcome the problem that

raised in peat soil. The effectiveness of this research are covered the applications

and implementations of post-cyclic method in the laboratory tested for peat soil

improvement.

7

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

It is well-known that Malaysia has very precious varieties of natural earth surface

even before the formation of the federation of Malaysia itself. Malaysia comprises

of the region of Peninsular Malaysia, Sabah and Sarawak. According to United

Nations Development Programme (UNDP, 2006), nearly 60 per cent of Malaysia or

about 19.5 million hectares is covered by forest of one type or another. Malaysia’s

tropical forest constitutes a significant component especially of peat soil that is

naturally available with an estimated 2.7 million hectares and predicted 1.54 million

hectares still remaining with the inclusion for more than 70 per cent of these peatland

forests are located in Sarawak, while less than 20 per cent of it is available in

Peninsular Malaysia and the remainder in Sabah as reported by the UNDP (2006).

At present, due to demands and human civilization necessities, large areas of

peat soil forests have already been cleared and converted for other uses and purposes.

The conversion aims to completely alter the landscapes for future development and

to take advantage of the land use in a more productive manner deemed fit for human

activities, settlements and industrial properties all in the name of economic

development for a greater Malaysia. The utilization of these peatlands in Malaysia is

one out of many options available, however, before compromising these peatlands

for construction, there are many economic factors that needs consideration, such as

budgets and others. Aside from that, the behaviour of the peat soil itself may result

in several major problems in the future after constructions which are highly related to

post-construction quality and productivity.

8

2.2 Peat Soil Definition

In Malaysia, some 3 million hectares of land is covered with peat. When

constructing roads or erecting any structures or human artificial edifices on

peatlands, the designer must understand both the common characteristics and failure

mechanisms that can initiate a peat slide. This is essential to ensure the construction

process does not trigger an unwanted event.

Peat materials can be characterized in various ways depending on the purpose

for which they are being used. Geotechnical engineers define peat soils as soils that

consist of organic content that is more than 75%, while soils that has organic content

below 75% is categorized as organic soils. However, in soil sciences, the soils that

have organic content more than 35% are classified as peat. In addition to that, the

definition of peat according to the ASTM D4427-13 (2013), peat is defined as soil

that is naturally available with high organic substance that is derived primarily from

plant materials. It is formed when organic matters, normally plant matters

accumulate more than it humidifies.

Duraisamy and Huat (2008) determine peat as a material that usually occurs

when organic matter is preserved below high water tables like in swamps or

wetlands. Consequently, with Ramsar’s (2002) statement, peatlands are wetlands

with a thick water-logged organic soil layer (peat) made up of dead and decaying

plant materials. Peatlands include moors, bogs, mires, peat swamp forests and

permafrost tundra.

9

2.3 Peat Content and Formation

Peats is a type of soft soil composed from high contents of fibrous organic matters

and is produced from partial decomposition and disintegration of mosses, sedges,

trees, and other plants that grow in marshes and other wet places in a condition

where there is a lack of oxygen, according to Kazemian et al., (2011a). Peat is a

mixture of fragmented organic materials formed in wetlands under appropriate

climatic and topographic conditions and it is derived from vegetation that has been

chemically changed and fossilized (Dhowian and Edil, 1980). In its natural state,

peats consist of water and decomposed plant fragments with virtually no measurable

strength (Munro, 2005).

Peats also contain high organic content, often more than 75%. The organic

contents present in peats are the remains of partially decomposed and disintegrated

plants. This happens in conditions where the rate of accumulation is more than the

rate of decay. Peats are accumulated if the rate of decay is slower than the rate of

addition (Bell, 2000). It accumulates whenever the conditions are suitable, that is, in

areas where there is an excess of rainfall and the ground is fully undrained,

irrespective of latitude or longitude.

Peat soil differs from mineral soil in several respects. Peat is a biogenic

deposit which was developed in the post-glacial (Holocene) period within the past

10,000 years. The formation of peat soil may vary in some places. Furthermore, the

content of peat may differ from location to location due to factors such as the origin

of fibres, temperature and degrees of humification. Decomposition or humification

involves the loss of organic matter either in gas or in solution, the disappearance of

physical structure and the change in chemical state (Kazemian et al., 2011b).

Therefore, the color of peat usually is dark brown or black and with a distinctive

odour (Craig, 1992). Since the main component is made up of organic matter, peat is

very spongy, highly compressible and combustible in characteristics (Bujang, 2004).

According to Jamil et al. (1989), whichever soil with a peat depth of <1.0, 1.0-1.5,

1.5-3.0 and >3.0m can be classified as shallow, moderate, deep and very deep peat.

Figure 2.1 shows peat subsidence measured in degraded peatlands to the east of the

Virgin Jungle Reserve in Pekan Forest Reserve. The degraded land has subsided up

to 2 m (Pahang Forestry Department 2005).

10

Figure 2.1: Peat subsidence at the eastern edge of South East Pahang Peat Swamp

forest at the transition from undisturbed forest to degraded peatland.

(Pahang Forestry Department - 2005).

2.4 Peat Location in Malaysia

Peat swamp is located in a few areas in Africa and parts of Central America,

but more than 60 per cent of the world’s tropical peat lands can be found in South-

East Asia. Estimated peatlands in Malaysia – 2.7 mil ha Peninsular Malaysia - 0.98

mil ha Sarawak - 1.66 mil ha Sabah - 0.80 mil ha (Mutalib et al., 1991) Peatlands are

usually found on highlands and poorly-drained lowlands. Highland peats are found

on small isolated areas in steep mountainous regions above 1000 mean sea level

(masl). Lowland peats are found in depressions near coastal areas. In Peninsular

Malaysia, peats are found in the Trans-Perak areas in the Perak Tengah and Hilir

Perak district, coastal areas of West Johore, Kuantan and Pekan districts, Rompin-

Endau area and Northwest Selangor. According to Mutalib et al., (1991) the state of

Sarawak has the largest peat area in the country with 16,500km² constituting 13% of

the state with 90% of it being more than 1 m deep.

Peats in Sarawak are found mainly between the lower stretches of the main

river courses and in poorly drained interior valleys. They are found in the

administrative divisions of Kuching, Samarahan, Sri Aman, Sibu, Sarikei, Bintulu,

Miri and Limbang. In Sabah, peat soils are found on coastal areas of the Klias

Peninsular, Krah swamp in Kota Belud, Sugut, Labuk estuaries and Kinabatangan

floodplains. Peat soils in Sarawak occur in large basin swamps and in small interior

valleys that have been developed in comparatively recent times (Andriesse, 1988).

Table 2.2 shows the estimated extent of peat coverage in Malaysia that is published

by the United Nations Development Programme (UNDP), Malaysia in 2006.

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Table 2.2: The estimated extent of peat cover in Malaysia

(United Nations Development Programme - UNDP. Malaysia – 2006)

Location

(State)

Total Area

(hectares)

Selangor 76,000

Johor 13,000

Terengganu 13,000

Pahang 200,000

Sabah 120,000

Sarawak 1,120,000

Peatlands are found just beyond the coastline on both east and west coasts of

Peninsular Malaysia. According to Bujang (2004), there are 3 million hectares or 8%

area in Malaysia covered with peat.

2.5 Classification of Peat Soil

According to Ajlouni (2000), there are many types of classifications avaliable to

classify peat soils. The physical, chemical, and physicochemical properties of peat

soils such as texture, organic content, pH, colour, moisture content, and the degree of

decomposition could serve as a basis for peat classification. Hobbs (1986) stated

that, those physical properties should be included in a full description of the peat soil.

These attributes are influenced by the main components of the formation such as

mineral content, organic content, moisture content and air respectively. Generally,

peat is grouped into two categories; amorphous peat and fibrous peat. Amorphous

peats are peats containing less than 20% of fibre content. It contains mostly particles

of colloidal size (less than 2 microns), and the pore water is absorbed around the

particle surface. Fibrous peats are defined as peats that contains more than 20% of

fibre content. Both, amorphous and fibrous peat has their own specific

characteristics.

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According to the Canadian and US Taxonomy, this order is further divided into

3 suborders based on the degree of decomposition of the organic matter and is

defined as Fibric, Hemic and Sapric. The Fibric is dominated by fibric peats which

contains undecomposed to weakly decomposed organic material with over 66% of

fibre content. The Hemic and the Sapric suborders are dominated respectively by

hemic peats, which are formed with moderately to well decomposed organic

materials with 33 – 66% of fibre content and by sapric peats which are formed by

strong to completely decomposed organic materials with less than 33% of fibre

content. Under the current soil classification, the Organic Soil Groups are separated

into two Subgroups according to the type of organic materials, thickness of organic

materials, ash content, groundwater table, and nature of mineral substratum. The

convexity of coastal and deltaic peat swamps surfaces are increasingly more

pronounced with its distance from the sea (Mutalib et al., 1992). In its natural state,

the water table is always high, often at or near the surface (Tie and Kueh, 1979).

Table 2.3 shows the Malaysian peat characteristics. Generally, the topography of

peat soil within Peninsular Malaysia and Sabah comparatively are flat, unlike the

ones in Sarawak where surface strata where is more dome-shaped. Table 2.4 shows

the criteria of Von Post Scale for assessing peat decomposition.

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Table 2.3: Characteristic of peat swamps in Malaysia

(Muttalib et al., 1991)

The Von Post scale begins from H1 to H10. H1 is classified as containing little

decomposed fibrous and light-coloured peat. While H10 is classified as containing

well decomposed, colloidal and dark-coloured material. Peat at scale H1-H3

indicates qualifying terms for fibric, H4-H6 is hemic with moderately decomposed

and H7-H10 is sapric or amorphous.

Region Location Topography Total Area Characteristics

Peninsular

West Johore,

Kuantan, Pekan,

Selangor, Perak

Peat land is flat

Approximately

80,000km2 with

89% of it

having deep

peat (>1m)

Normally found in the

coastal areas of the east

and west

coasts

Sarawak

Kuching,

Samarahan,

Sri Aman, Sibu,

Sarikei, Bintulu,

Miri and

Limbang

The basin peat

swamps are

dome-shaped

16500 km2 with

89% of it

having deep

peat

(>1m)

Peat occurs mainly

between the lower

stretches of

the main river courses

(basin

peats) and in poorly

drained interior valleys

(valley peats).

Sabah

Kota Belud,

Sugut,Labuk,

Kinabatangan

Peat land is flat

86 km2. There

were no

estimates on

the depths

Peat soils are found on

the coastal areas

14

Table 2.4: The Von Post Scale for Assessing Peat Decomposition

(science.ulst.ac.uk/vft/vonPost, 2014)

Degree of

Decomposition

Nature of

Squeezed

Liquid

Proportion

of Peat

Extruded

Nature of Plant

Residues Description

Fibric

H1 Clear,

Colourless None

Plant structure

unaltered

Fibrous, elastic

Undecomposed

H2

Almost clear,

yellow-brown None

Plant structure

distinct, almost

unaltered.

Almost

undecomposed

H3 Slightly turbid,

brown None

Plant structures

distinct, most

remains easily

identifiable

Very weakly

decomposed

Hemic

H4 Strongly turbid,

brown None

Plant structure

distinct, most

remains identifiable

Weakly

decomposed

H5

Strongly turbid,

contains a little

peat in

suspension

Very little

Plant structure clear

but indistinct and

difficult to identify

Moderately

decomposed

H6

Muddy, much

peat in

suspension

One third

Plant structure

indistinct but clearer

in residue, most

remains undefinable

Well

decomposed

Sapric

H7 Strongly muddy One half Plant structure

indistinct

Strongly

decomposed

H8 Thick mud,

little free water Two thirds

Plant structure very

indistinct – only

resistant material

such as roots

Very strongly

decomposed

H9 No free water Nearly all

Plant structure

almost

unrecognisable

Almost

completely

decomposed

H10 No free water All

Plant structure not

recognisable,

amorphous

Completely

decomposed

15

Figure 2.2 shows the profile and stratum of peat soil in line with the

classification of soil in Sarawak (Mutalib et al., 1992). An upper layer (20 – 30 cm

thick) consist of well-decomposed organic materials of the sapric type, the middle

layer (30 – 40 cm thick) however, consist of semi-decomposed organic materials of

the hemic type while the lower layer of fibric materials is mainly made up of large

wood fragments and branches as well as tree trunks (Mutalib et al., 1992)

c

Figure 2.2: Profile morphology of drained organic soils

(Source: Modified from Mutalib et al., 1992)

2.6 Physical and Engineering Characteristics of Peat

Peats originate from plants and denotes the various stages in the humification process

where the plant structures can be determined (Deboucha et al., 2008). The decaying

process of plants under acidic conditions without microbial process will result in the

formation of organic matters in the peats. This condition renders the peats extremely

soft and can be concluded as problematic soil. Thus, this study is conducted to

examine and comprehend the particularities of peat engineering behaviour in respect

to the compressibility and various characteristics to establish suitable correlation

when seeking their indexed properties such as natural water content, organic content,

liquid limit, specific gravity and density. According to Deboucha et al., (2008),

peats have certain characteristics that require special consideration and set up from

that of mineral soils.

Remnants of decom p osin g wood / trunks

Semi decomposed wood/log/trunk

Sapric

Hemic

Fibric

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Peats occur as extremely soft, wet and unconsolidated surficial deposits.

According to Bujang (2004) peats are geotechnically problematic due to their high

compressibility and low shear strength. In a moderate load increment, it may lead to

large volume changes that showes high compressibility. Deep peats exhibit high

compressibility, medium to low permeability, low strength and volume instability as

described by Wong (2008). Peats are also characterized by high initial void ratio,

organic content and water holding capacity (Deboucha et al., 2008).

For civil engineering purposes, it is essential to describe organic soils or peats.

Therefore some essential indexed properties of these soil conditions are needed in-

order to classify them and find the best ways to counter their negative effects on the

designed imposed loads. The following characteristics are suggested by Hobbs

(1986) and Edil (1977) to describe the properties of peat.

a) Colour, and odour

b) Water content

c) Degree of humification

d) Fibre content

e) Liquid limit and plastic limit

f) Principal plant component, namely coarse fibre, fine fibre,

amorphous granular material and woody material

g) Grain size distribution

h) Density and Specific Gravity

i) Atterberg Limits

Tests should be conducted to determine and identify the major components of

engineering properties and it is essential to conduct various types of tests. These test

can be divided into two categories: physical and mechanical tests. Visual inspection

of the soil such as the soil’s appearance, colour, possible odour and plasticity are

classified as physical tests, which would then be followed by the indexed property

tests and mechanical property tests. However, all these methods must be

supplemented by other procedures leading to quantitative results that may be related

to the physical properties with which the engineer is directly concerned (Peck et al.,

1974).

17

Since the main component is an organic matter, peats are very spongy, highly

compressible and combustible in characteristics (Shafiee et al., 2013). These

characteristics make the peats to pose its own distinctive geotechnical properties as

compared to other inorganic soils like clay and sandy soils which are made up of

only soil particles (Deboucha et al., 2008).

Table 2.5 shows tabulated peat soil properties in Malaysia from previous

studies. In the tabulated data from past researchers, the Atterberg limit parameters

for plastic limit and plasticity index in some conditions are not shown due to the soil

samples used for testing have very low clay content, while the liquid limit and plastic

limit tests may not produce reliable results according to Whitlow (2001). Natural

water content as recorded, ranges from 200 per cent to 2200 per cent for East

Malaysia and the range of 230 per cent to 500 per cent was found in Johor Hemic

peats (Zainorabidin and Bakar, 2003). Acidity of peat soils from past research were

recorded as 3.51 on the pH scale while the highest reading was 6.18 on the pH scale.

Thus, researchers explained that the reason is due to high water content and active

composition systems. In subsequent parameters, fibre contents for peat soils were

recorded in ranges between 30 to 91%. In addition to these parameters, there were

also specific gravity components that mostly recorded between 1.0 and 2.0.

Zainorabidin and Bakar (2011) followed by Aminur and Kolay (2011) recorded

values of plasticity index for Western Johor peats where the presence of clay were

spotted in the peats sampled. It is best to inspect its grain size properties before

proceeding with the Atterberg Limits test if the presence of fines is more than 35%

(NZ Geotechnical Society, 2005) in accordance to the BS5930, where liquid limit

and plastic limit needs to be conducted thereafter to identify its plasticity.

18

No.

Researcher Atterberg Limit (%) Natural

water

Content

(w, %)

Specific

gravity

(Gs)

Bulk

density

(Mg/m3)

Acidity

(pH)

Organic

content

(%)

Void

ratio,

(e)

Fiber

content

(%) Ip wL

1 Deboucha et al., (2008) 57.95 115.8 700-850 1.343 1.059 4.6 - 10.99 -

- 285 266 1.52 0.922 - 76 7.541 65

- 350 330 1.45 0.834 - 84 9.535 75

- 398 350 1.42 0.811 - 88 10.480 77

2 Duraisamy and Huat (2008) - 250 181 1.55 1.008 - 73 5.522 55

- 275 241 1.53 0.856 - 75 6.536 58

- 240 140 1.56 1.019 - 70 4.125 32

- 310 286 1.51 0.956 - 77 7.895 68

- 330 300 1.49 0.996 - 80 4.824 31

3 Wong et al., (2008) - - 668 1.40 - 3.51 96 - 90

4 Hashim and Islam (2008a) - 208.4 414-674 0.95-1.34 1040.41 3.51 99.06 7.999 90.25

5 Wong et al. (2009) - - 668.30 1.40 1038.00 3.51 96.50 9.30 90.40

6 Islam and Hashim (2008b) - - 555 1.24 - 3.51 96.45 - 90.39

7 Faisal (2008) - - 668.30 1.396 1037.72 3.51 96.45 9.329 90.39

8

Zainorabidin and Bakar (2011) 90-160 190-360 200-700 1.38-1.70 - - 65-97 - -

85-297 210-550 200-2200 1.07-1.63 - - 50-95 - -

- 220-550 230-500 1.48-1.8 - - 80-96 - -

9

Aminur and Kolay (2011)

78 - 620.14 1.45 - 4.05 85.10 - 65.00

79 - 473.70 1.62 - 4.64 78.88 - 63.45

73 - 360.72 1.64 - 5.15 66.60 - 61.40

75 - 787.04 1.48 - 4.25 82.40 - 64.25

77 - 623.76 1.56 - 4.33 80.85 - 63.55

Table 2.5: Tabulated of Peat Soil Properties in Malaysia

Note: - = Nil

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This research work deals with a study on the post cyclic behaviour of peat soils

analysed using dynamic and static methods. The application of effective stresses and

frequencies are critically reviewed using triaxial tests. A series of triaxial tests were

carried out to investigate the influence of dynamic loading on shear strength. Table

2.6 has been summarized to show the differences between disturbed and undisturbed

samples by the means of their definition, procedure and the use of samples

respectively. Table 2.7 summarizes the features of the indexed properties tests with

definitions and significances of the tests used. The denomination of indexed

properties provide valuable information when the results are compared to empirical

data that is relative to the indexed properties determined for peat classification.

PVC used in undisturbed sampler, is recommended by Munro and MacCulloch

(2006) as this is a low cost system for attaining peat soil samplings. They have

concluded that, the achieved results are due to the sampler being driven down into

the peat by the means of a lightweight percussive machine or gent tappings with a

hammer. Sina et al., (2011) recommends using a tube sampler after the wax has

been dried, and subsequently sealed using foil and sealer to prevent any losses or

gains of moisture and is placed in a container.

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Table 2.6: Summary of Disturbed and Undisturbed Samples Differences.

Description Disturbed Sample Undisturbed Sample

Definition A quantity of soil without any

particular concern for the

condition of the soils.

(Zolkefle, 2014).

A quantity of soil where the

moisture content of soil, the void

ratio, soil structure and also its

constituents are handled with care

without any disturbances and

interruption (Zolkefle, 2014).

Characteristic Change in the stress

condition.

Change in the water

content and the void

ratio.

Disturbance of the soil

structure.

(Huat, 2004)

No change due to disturbance

of the soil structure,

No change in void ratio and

water content,

No change in constituents

and chemical properties.

(Huat, 2004)

Procedure Excavate the soil using

shovel.

Placed the sample in

heavy duty plastic bag

and kept in container.

Kept in normal

temperature in

laboratory.

Sampler penetrated into soil in

required depth.

In vertical condition.

Trimmed and dredged out

carefully.

Waxed at both ends

immediately.

Sealed the sampler with

aluminum foil and wrapped

with plastic.

Placed in storage container.

Kept in cold room with

controlled constant

temperature.

Test to be

carried out Particle Size Distribution

Degree of Humification

Specific Gravity

Organic Content

Fiber content

Liquid Limit

pH test

Monotonic Triaxial test

Cyclic Triaxial test

Post-Cyclic Triaxial test

Moisture Content

21

Table 2.7: Summary of Definition and Significant Index Properties Tests.

Test Definition Significant

Particle Size

Distribution

A list of values that defines the

relative amount, typically by mass,

of particles present according to

size.

To determine the

percentage of various

sized soil particles in a

soil mass. For this

purpose, a particle size

distribution curve is

plotted.

Degree of

Humification

Describe the physical appearance of

soil based on the Von Post

classification.

A detail description on

classification of soil.

Specific

Gravity

Specify as the ratio of the mass of

dry soil to the mass of an equal

volume of water.

Specify the gravity of the

soil by using kerosene.

Moisture

Content

Presents the ratio of mass of water

and mass of dry solid particle at

1050C.

Clearly determined the

percentage of natural

moisture in that particular

peat.

Organic

Content

Covers the determination of the

percentage by dry mass of organic

matter present in a soil.

Organic content is an

important parameter

whereby the percentage

of peat and organic soils

and mineral soil (silt and

clay) should be differed.

Liquid Limit

The water content at which soil

passes from the plastic to the liquid

state under standard test conditions.

The limit is expressed as a

percentage of the dry weight of the

soil.

Its significant is to

identify to which state the

soil stress is presumed to

be mobilized.

Fiber Content

Determined typically from dry

weight of fibers retained on 0.15

mm as a percentage of oven-dried

mass and being set in the oven at

1050C.

The percentage of fiber in

the soil is obtained and

located in the range of

USDA classification.

pH Test

Use to describe the salinity of the

soil by using electrometric method.

Ensure the salinity of soil

is classified as acid or

alkaline.

22

2.7 Shear Strength of Peat Soil

According to Boylan and Long (2012), peats which are formed from the

accumulation of organic materials over thousands of years, are characterised by its

high water content, compressibility and low shear stiffness and shear strength.

As with mineral soils (silt and clay), the settlement parameters of peats such

as the consolidation settlement can be determined from a standard incremental

oedometer test (Edil, 2003). However, the overburden pressure of peats are very low

(Gosling and Keeton, 2006). The researcher discovers at the base of the 2 m thick

layer with water level at ground level, the effective stress is only about 2 kPa. They

compared it with an inorganic soil where the layer is of the same thickness and water

level as well, would impose a 20 kPa stress this is almost 10 times greater than the

peat soil. This shows that, peats have much lower strength.

Nonetheless, the effective shear strength of peat soils are essentially a

frictional material and that it behaves closely in accordance with the principles of

effective stress. Gosling and Keeton (2006) conclusively explained that standard

tests that consolidates undrained triaxial test with the measurement of pore water

pressure does not required over 50% axial strain to fail. However, tests can be carried

out and be interpreted to give similarly high effective stress values where only 20%

of axial strain is applied.

Bujang (2006) stated on his study on peat strength revealed that, some

confusion indicates the potential of peats to be treated as a frictional material like

sand or cohesive like clay. It is almost the same as the assumptions by Dhowian and

Edil (1980) where they explain that surficial peats are commonly encountered as

submerged surficial deposits. This is because of their low unit weight and

submergence, as such deposits develop very low vertical effective stresses for

consolidation and the associated peats exhibit high porosities and hydraulic

conductivities that are comparable to those of fine sand or silty sand. Bujang (2006)

also states that peats with such materials can be expected to behave like “drained"

soils such as sand when subjected to shear loading. On the other hand, soils with

consolidation shows a rapid decrease in porosity and hydraulic conductivity becomes

comparable to that of clay. There is a rapid and immediate transition from a well-

drained material to an undrained material (Edil et al., 1994).

23

Gosling and Keeton’s (2006) assessment on the geotechnical properties of

peats are made complex by its high water content and compressibility, as well as its

organic composition. Acknowledging the high compressibility of peats and the need

to break fibres during sampling makes obtaining high quality samples difficult and

disturbed samples may display non-conservative parameters of stability in the

assessments especially when it comes to an increased in strength.

Shear strength is the primary controlling factor in peat failures. This research

adduces an understanding of the shear strength variations through peat soils that

provide an indication of the likely stability of the peats during pre and post

construction that are close to road construction works. Aside from that, it is also

related to the interest of static and dynamic loading study. Due to this study of shear

strength behaviour of peat soils, Gosling and Keeton (2006) describes the causal

factors of peat failures through an examination of the soil behaviour during a peat

failure which could range from the undrained such as sudden loading or a short

duration of extreme rainfall. As for drained characteristics, do expect noticeable

features like drying and cracking of peats during summer or the creep of peats when

there is a significant change in the slope angle. The range of permeability values

reported for peats and its potential to change significantly under modest loading

(Mesri and Ajlouni, 2007) adds further uncertainties, and one of it being the

appropriate drainage conditions that needs consider.

Boyland et al., (2008) explains that the Undrained shear strength (su) refers to

the strength of soil in situations where the excess pore water pressures developed

during shearing cannot dissipate and failure takes place. Whereas in mineral soils,

failure occurs as a result of a reduction in effective stress brought about by the

increase in pore water pressure. Not knowing the effective stress principle in its

classical form in peats make the application of undrained shear strength

correspondingly doubtful. Figure 2.3, showes the Relationship between shear

strength, moisture content and degrees of humification. The shear strength of peat

soil is measured no matter it is drained or undrained strength. From Figure 2.3, it can

be seen that the shear strength of peat decreases when water content increases.

24

Figure 2.3: Relationship between Shear Strength, Moisture Content

and Degree of Humification

(Helenlund 1980:, Boyland et al., 2008)

2.7.1 Undrained Strength

According to Boylan and Long (2012), peats which are formed from the

accumulation of organic materials over thousands of years, are characterised by its

high water content, compressibility and low shear stiffness and shear strength.

As with mineral soils (silt and clay), the settlement parameters of peats such

as the consolidation settlement can be determined from a standard incremental

oedometer test (Edil, 2003). However, the overburden pressure of peats are very low

(Gosling and Keeton, 2006). The researcher discovers at the base of the 2 m thick

layer with water level at ground level, the effective stress is only about 2 kPa. They

compared it with an inorganic soil where the layer is of the same thickness and water

level as well, would impose a 20 kPa stress this is almost 10 times greater than the

peat soil. This shows that, peats have much lower strength.

Nonetheless, the effective shear strength of peat soils are essentially a

frictional material and that it behaves closely in accordance with the principles of

effective stress. Gosling and Keeton (2006) conclusively explained that standard

tests that consolidates undrained triaxial test with the measurement of pore water

171

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