INSTRUMENTED PHYSICAL MODEL STUDIES OF THE PEAT SOIL-
ENGINEERING STRUCTURE INTERACTION
SITI NOORAIIN BT MOHD RAZALI
A thesis submitted in
fullfillment of the requirement for the award of
The Master Degree of Civil Engineering
Faculty of Civil and Environmental Engineering
Universiti Tun Hussein Onn Malaysia
SEPTEMBER 2013
vi
ABSTRACT
The engineering structures are mostly constructed directly in contact with the ground
and the response between the soil and the structure is termed as soil-engineering
structure interaction. To understand the interaction, physical modelling is considered as
a prime method of study. This physical model study has been conducted on peat soils
obtained from the Malaysian Agricultural Research and Development Institute-
Integrated Peat Research Station (MARDI-IPRS) in Pontian, Johor. Peat is considered
as unsuitable soil for supporting foundations in its natural state due to the high moisture
content (>100%), high compressibility (0.9-1.5) and low shear strength (5-20 kPa)
values. Peat also contains high organic matter (>75%), large deformation, high
compressibility and high magnitude and rates of creep. The objectives of this study are
to identify the engineering characteristic of the peat, analyse the deformation behaviour
in peat soil based on physical modelling, analyse using physical model the stress
distribution beneath the structure in peat soil and to compare the peat behaviour with
sand. The reason of comparing these two different types of soil was to obtain the
significant difference in terms of the settlement, stress and failure pattern. This study
also helps to acquire basic understanding of the behaviour of settlement and stress of
peat soil when load is applied to it. The rectangular model and the square model were
used in pre-model study (PMS) to identify suitable indicators and observed the
deformation of the peat/sand after the loading process. Meanwhile, a plane strain model
cm was used in plain strain study (PSS) with instrumentations (Displacement
Transducers and Soil Pressure Gauge) to investigate and observed the settlement and
stress on the peat/sand. Various static loads were applied at the surface and the
interaction between peat soil and sand with the structure was recorded based on all the
deformations and stresses at various positions and levels. The water level was
maintained at a constant level that is at the surface of the soil to prevent any induce
stress due to the seepage of water and to omit settlement due to the lowering of the
water table. The observations showed that the settlement in peat was higher compared to
the settlement in sand because of the properties of peat that highly compressible
compared to sand. The deformation of sand corresponds to general bearing capacity
failure and deformation in peat shows punching shear failure. However, the stress in the
sand was higher than the stress in peat because of the presence of water that affects the
value of stress in peat.
vii
ABSTRAK
Struktur kejuruteraan kebanyakannya di bina secara langsung menyentuh permukaan tanah
dan tindak balas di antara tanah dan struktur di panggil sebagai interaksi struktur
kejuruteraan – tanah. Untuk memahami interaksi, model fizikal dianggap sebagai kaedah
utama kajian. Model fizikal ini telah dijalankan ke atas tanah gambut yang di perolehi dari
Malaysian Agricultural Research and Development Institute-Integrated Peat Research
Station (MARDI-IPRS) di Pontian, Johor. Gambut di anggap sebagai tanah yang tidak
sesuai untuk menyokong asas dalam keadaan smulajadi kerana nilai kandungan lembapan
yang tinggi (>100%), kebolehmampatan yang tinggi (0.9–1.5) dan kekuatan ricih yang
rendah (5– 20 kPa). Gambut juga mengandungi kadungan organik yang tinggi (>75%), ubah
bentuk yang besar, kebolehmampatan yang tinggi, magnitud dan kadar rayapan yang tinggi.
Objektif kajian adalah untuk mengenalpasti ciri-ciri kejuruteraan tanah gambut, analisis,
analisis kelakuan ubah bentuk di dalam tanah gambut berdasarkan model fizikal, analisis
dengan menggunakan model fizikal untuk agihan tegasan di bawah struktur di kawasan
tanah gambut dan untuk bandingkan kelakuan gambut dan pasir. Kedua-dua jenis tanah ini
dibandingkan adalah untuk mendapatkan perbezaan ketara dari segi enapan, tekanan dan
corak kegagalan. Kajian ini juga membantu untuk pemahaman asas tingkah laku enapan dan
tekanan tanah gambut apabila beban dikenakan kepadanya. Model segi empat tepat dan
model segi empat sama telah digunakan dalam kajian pra-model (PMS) untuk mengenal
pasti penunjuk yang sesuai dan memerhatikan ubah bentuk gambut/pasir selepas proses
pembebanan. Sementara itu, model terikan kosong telah digunakan dalam kajian terikan
kosong (PSS) dengan instrumentasi (Displacement Transducers dan Soil Pressure Gauge)
untuk menyiasat dan memerhatikan enapan dan tekanan pada gambut/sand. Sifat – sifat
indeks dan sifat – sifat kekuatan tanah gambut juga telah ditentukan. Model PSS telah
dibina untuk menguji gambut dan pasir. Pelbagai beban statik telah digunakan di permukaan
dan interaksi antara tanah gambut dan pasir dengan structur di catatkan berdasarkan ubah
bentuk dan tekanan pada pelbagai kedudukan dan tahap. Paras air dikekalkan pada tahap
yang tetap iaitu berada pada permukaan tanah untuk mengelakkan sebarang tekanan aruhan
disebabkan oleh resapan air dan untuk abaikan enapan yang disebabkan oleh penurunan aras
air. Pemerhatian menunjukkan bahawa enapan tanah gambut lebih tinggi berbanding enapan
pasir disebabkan oleh cirri-ciri tanah gambut yang tinggi kemampatan berbanding pasir.
Ubah bentuk pasir adalah sepadan dengan kegagalan keupayaan am dan ubah bentuk pada
gambut menunjukkan kegagalan ricih menebuk. Walaubagaimanapun, tekanan dalam pasir
adalah lebih tinggi berbanding tekanan pada tanah gambut kerana kehadiran air
mengurangkan nilai tekanan di dalam tanah gambut.
viii
CONTENTS
TITLE i
DECLARATION ii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT vi
CONTENTS viii
LIST OF TABLES xiii
LIST OF FIGURES xiv
LIST OF SYMBOLS AND ABBREVIATIONS xix
LIST OF EQUATIONS xx
LIST OF APPENDIX xxi
CHAPTER 1 INTRODUCTION 1
1.1 Preamble 1
1.2 Description of Problems 3
1.3 Objectives 6
1.4 Scope of Study 6
1.5 Importance and Contribution of Study 9
1.6 Organization of Thesis 9
1.7 Tests Schedule 11
CHAPTER 2 LITERATURE REVIEW 12
2.1 Introduction 12
2.2 Peat Soil 13
2.2.1 Definition of Peat 13
2.2.2 Classification 14
2.2.3 Peat Characteristics and Properties 18
2.3 Sand 20
2.3.1 Definition and Formation 20
2.3.2 Classification and characterization 21
ix
2.4 Behaviour of Soil under Static Loading 22
2.4.1 Settlements 22
2.4.1.1 General 22
2.4.1.2 Sand 24
2.4.1.3 Peat 26
2.4.2 Stresses due to external load 29
2.4.3 Pore Water Pressure 32
2.5 Challenges on Peat 32
2.6 Modes of Failure 33
2.7 Case Studies 36
2.7.1 The Bereng Bengkel Trial Embankment 37
2.7.2 Physical Modelling of Railway Embankments on Peat
Foundations 38
2.7.3 Instrumentation and Analysis of a Railway Embankment
Failure Experiment 40
2.7.4 Construction on Soft Soil with “Akar Foundation” 44
2.7.5 Surcharging as a Method of Road Embankment Construction on
Organic Soils 45
2.8 Indicator 48
CHAPTER 3 MARDI-IPRS PEAT 50
3.1 Introduction 50
3.2 Site Sampling 50
3.3 Sample Preparation 54
3.4 Method for Peat Identification 56
3.4.1 Index Properties Tests 57
3.4.1.1 Von Post Scale of Humification 57
3.4.1.2 Moisture Content 58
3.4.1.3 Specific Gravity 59
3.4.1.4 Organic Content 60
3.4.1.5 pH 61
3.4.1.6 Atterberg Limits 61
x
3.5 Pontian Peat Soil Characteristics 62
3.5.1 Index Properties 63
3.6 Chapter Summary 66
CHAPTER 4 PRE- MODEL STUDY (PMS) 67
4.1 Introduction 67
4.2 Experimental Apparatus 67
4.2.1 Model Container 67
4.2.2 Model Design and Load 69
4.2.3 Model Construction and Testing Procedure 71
4.2.3.1 Indicator 71
4.2.3.1.1 Coal and Laterite 72
4.2.3.1.2 Polystyrene and Sand 75
(a) Polystyrene 76
(b) Sand 77
(c) Comparison of Polystyrene and Sand 78
4.2.3.2 DT Plate Size 81
4.3 Evaluation of Apparatus (results) 82
4.3.1 Indicator 82
4.3.1.1 Sand 82
4.3.1.2 Peat 84
4.3.1.3 Comparison of Failure in Sand and Peat 91
4.3.1.4 Displacement Transducer‟s Plate Size 93
4.3.1.5 Pre Model Study Setup 94
4.4 Chapter Summary 95
CHAPTER 5 PLANE STRAIN STUDY (PSS) 97
5.1 Introduction 97
5.2 Description of the 2D Small Scale Model 98
5.2.1 Model Design 98
5.2.1.1 Instrumented Section 100
5.2.2 Data Logger Setting 102
xi
5.2.3 Instrumentations 106
5.2.3.1 Types of Instrumentations 106
5.2.3.2 Procedure of Calibration 108
(a) Displacement Transducer (DT) 108
(b) Soil Pressure Gauge (SPG) 109
(c) Pore Pressure Gauge (PPT) 110
5.2.3.3 Installation of Instrumentations 110
(a) Displacement Transducer (DT) 110
(b) Soil Pressure Gauge (SPG) 111
(c) Pore Pressure Transducer (PPT) 112
5.3 Model Construction and Testing Procedure 114
5.3.1 Introduction 114
5.3.2 Plane Strain Study for Peat 117
5.3.3 Plane Strain Study for Sand 118
5.3.3.1 Dry Sand 118
5.3.3.2 Wet Sand 119
5.3.4 Loading 120
5.3.5 Maintenance 121
5.4 Evaluation of Apparatus (Results) 122
5.4.1 Calibrations Data 123
5.4.1.1 Displacement Transducers 123
5.4.1.2 Soil Pressure Gauges 123
5.4.1.3 Pore Pressure Transducers 124
5.4.2 Plane Strain Study for Peat 124
5.4.3 Plane Strain Study for Sand 125
5.4.3.1 Dry Sand 125
5.4.3.2 Wet Sand 126
5.5 Summary 127
xii
CHAPTER 6 RESULTS AND ANALYSIS 128
6.1 Introduction 128
6.2 Settlements 129
6.2.1 Calculated Settlements 129
6.2.2 Measured Settlements using Gridlines Marker 131
6.2.3 Measured Settlements using Instrumentations 134
(a) DT 1 134
(b) DT 2 135
(c) DT 3 136
(d) DT 4 137
(e) DT 5 138
(f) DT 6 139
(g) Summary 140
6.2.4 Settlements: Calculated, Measured by instruments and by
Gridlines 143
6.3 Stresses 145
6.3.1 Calculated Stresses 145
6.3.2 Measured Stresses 151
6.3.3 Stress: Calculated and Measured 159
6.4 Summary 161
CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS 162
7.1 Conclusions 162
7.2 Critical Overview of Study 163
7.3 Assumptions and Limitations 165
7.4 Precaution during the Experiments 165
7.5 Significance of Study 166
7.6 Recommendations for Further Study 167
REFERENCES 168
xiii
LIST OF TABLES
Table 1. 1: Characteristics of Peat Swamps in Malaysia 2
Table 1.2: Schedule of Tests Conducted 11
Table 2. 1: Different Descriptions of Peat 14
Table 2. 2: Classification of Peat 15
Table 2. 3: The Von Post Scale of Humification 17
Table 2. 4: Index Properties of Peat 19
Table 2. 5: Properties of Peat Soil in Malaysia 20
Table 2. 6: Soil Classification System 21
Table 2. 7: Challenges on Peat 33
Table 2. 8: Physical Properties of Organic Soils at Antoniny Site 46
Table 2.9: Types of indicator used by past researchers 48
Table 3.1: Testing and Standard Methods 56
Table 3.2: Classification of Peat 63
Table 3. 3: Properties of Peat Soil Compared to Past Researchers 65
Table 4.1: Box Dimensions 68
Table 4. 2: Sand Size Selection 87
Table 4. 3: Conclusion for the indicator of peat 90
Table 6. 1: Summarize of Maximum Settlement 140
Table 6. 2: Settlement from Calculated, Measured and Gridlines Marker 143
Table 6. 3: Example of Stress Calculation 147
Table 6. 5: Measured Stresses 154
xiv
LIST OF FIGURES
Figure 1. 1: The distribution of Peat in Malaysia 2
Figure 1.2: Settlement in the Housing Area, Sibu, Sarawak 4
Figure 1.3: Settlement for (a) pipeline and (b) lamp post near Salim-Airport Road
By-Pass, Sibu, Sarawak 5
Figure 1.4: Settlement on Peat Soil, Parit Nipah, Johor 6
Figure 1. 5: Flow Chart 8
Figure 2.1: Summary of Literature Review 13
Figure 2. 2: Compression Index versus Consolidation Pressure 15
Figure 2. 3: Distribution of Pressure 29
Figure 2. 4: Vertical stress below the corner of a uniformly loaded flexible
rectangular area 30
Figure 2. 5: Increase of stress below a rectangular loaded flexible area 31
Figure 2.6: General Shear Failure 34
Figure 2.7: Local Shear Foundation Failure 35
Figure 2.8: Punching Shear Failure 35
Figure 2. 9: The Results of Compression Tests of Peat 39
Figure 2. 10: View of Models and Prototypes with Stages of Deforming 40
Figure 2.11: Car Numbering 41
Figure 2.12: The Embankment Failure 42
Figure 2. 13: Selected Transverse Displacement Measured with Total Stations 43
Figure 2. 14: Selected Settlement Tube Measurements 43
Figure 2. 15: Settlement Tube Readings under the Embankment 43
Figure 2. 16: Load Test of the Foundation System: The arrow marker indicated the
soil bed level (settlement) under different loads 45
Figure 2.17: Vertical Settlements in the Organic Subsoils at Antoniny Site 47
Figure 2. 18: Horizontal Displacement at Antoniny Site 47
xv
Figure 3.1: Site Study 51
Figure 3.2: Site for Sampling 51
Figure 3.3: Soil Profiling using Peat Auger 52
Figure 3.4: Soil Profile 53
Figure 3.5: Peat Sampling Process 53
Figure 3.6: Peat with Large Woody Fragments 54
Figure 3.7: Sample Preparation 55
Figure 3. 8: Squeezed Peat 57
Figure 3. 9: Moisture Content 58
Figure 3. 10: Specific Gravity Apparatus 59
Figure 3.11: Organic Content 60
Figure 3.12: pH 61
Figure 4.1: Model for Pre-Model Study 70
Figure 4.2: Indicator for Sand 73
Figure 4.3: Construction Steps for Small Model 74
Figure 4.4: Set up for Square Box 75
Figure 4.5: Polystyrene as an Indicator 76
Figure 4.6: Construction Process 77
Figure 4.7: Testing for Size of Sand as an Indicator 78
Figure 4.8: Test to Identify the Suitable Indicator 79
Figure 4.9: The Different Indicators Test 80
Figure 4.10: Loading Process 81
Figure 4.11: Suitable Plate Sizes 81
Figure 4.12: Indicator for Sand 83
Figure 4. 13: Settlement Pattern with the Increasing of Load 84
Figure 4. 14: Polystyrene as an Indicator 85
Figure 4.15: Sand as an Indicator 86
Figure 4.16: Test for Sand Sizes Selection 88
xvi
Figure 4.17: Result for the Most Visible 89
Figure 4.18: Sand Absorb the Water and Affect the Settlement of Peat 91
Figure 4. 19: Failure Pattern 92
Figure 4.20: Tests to Determine the Plate Size 93
Figure 4.21: Setup for PMS 95
Figure 5.1: Overview of Test (a) Peat and (b) Sand 99
Figure 5.2: Location of DT (Plan View) 100
Figure 5.3: Location of Soil Pressure Gauge (Plan View) 101
Figure 5.4: Location of Pore Pressure Transducers (Front View) 102
Figure 5.5: Setting for Environment 103
Figure 5.6: File Name 103
Figure 5.7: Steps to Set the Interval Time 104
Figure 5.8: MEAS Setting 105
Figure 5.9: Instrumentations for Monitoring 107
Figure 5.10: Calibration for DT 109
Figure 5.11: Different Load Applied to SPG 109
Figure 5.12: PPT at Different Depth 110
Figure 5.13: Installation of DT 111
Figure 5.14: Installation of SPG into Holder 111
Figure 5. 15: Installation of PPT into the Wall Box 112
Figure 5.16: Location of Instrumentations 113
Figure 5.17: Data Logger Connection 113
Figure 5.18: Plastic Sheeting to Minimize Friction 114
Figure 5.19: Grid Paper as Settlement Marker 115
Figure 5.20: Detailed of Large Box 116
Figure 5.21: The Construction of Physical Model Study on Peat Soil 117
Figure 5.22: The Construction of Physical Model Study on Dry Sand 118
Figure 5.23: The Construction of Physical Model Study on Wet Sand 119
xvii
Figure 5.24: Location of Load and DT in (a) Peat and (b) Sand 120
Figure 5.25: Maintenance Process 122
Figure 5. 26: Displacement Pattern in Peat 124
Figure 5. 27: Displacement Pattern in Dry Sand 125
Figure 5. 28: Displacement Pattern in Wet Sand 126
Figure 6. 1: Calculated Settlement on Sand and Peat 130
Figure 6. 2: Deformation Patterns 131
Figure 6.3: Maximum Settlement (Gridlines) 133
Figure 6.4: Settlement for Dry Sand, Wet Sand and Peat at DT1 134
Figure 6. 5: Settlement for Dry Sand, Wet Sand and Peat at DT2 135
Figure 6. 6: Settlement for Dry Sand, Wet Sand and Peat at DT3 136
Figure 6. 7: Settlement for Dry Sand, Wet Sand and Peat at DT4 137
Figure 6. 8: Settlement for Dry Sand, Wet Sand and Peat at DT5 138
Figure 6.9: Settlement for Dry Sand, Wet Sand and Peat at DT6 139
Figure 6. 10: Maximum Settlement (Instrumentations) 141
Figure 6. 11: Settlement Increases with Load Increases for Dry Sand 142
Figure 6. 12: Calculated versus Measured Settlement 144
Figure 6. 13: Area Divided into Four Rectangles 146
Figure 6. 14: Different Depth, Same Distance (76 cm c-c) 147
Figure 6. 15: Different Depth, Same Distance (38 cm c-c) 148
Figure 6. 16: Different Depth, Same Distance (0 cm c-c) 148
Figure 6. 17: Different Distance, Same depth (H=20 cm) 149
Figure 6. 18: Different Distance, Same depth (H=40 cm) 149
Figure 6. 19: Different Distance, Same depth (H=60 cm) 150
Figure 6. 20: Stress Isobars 150
Figure 6. 21: Measured Stress at Different Depth, Same Distance (76 cm) 152
Figure 6. 22: Measured Stress at Different Depth, Same Distance (38 cm) 152
Figure 6. 23: Measured Stress at Different Depth, Same Distance (0 cm) 153
xviii
Figure 6. 24: Measured Stress at Different Distances, Same Depth (H=20 cm) 156
Figure 6. 25: Measured Stress at Different Distances, Same Depth (H=40 cm) 156
Figure 6. 26: Measured Stress at Different Distances, Same Depth (H=60 cm) 157
Figure 6. 27: Stress Isobars 158
Figure 6. 28: Calculated and Measured Stress 159
xix
LIST OF SYMBOLS AND ABBREVIATIONS
∆σ Increase of stress
σ′0 Effective overburden pressure
∆σ′ Effective pressure
µs Poisson‟s ratio of soil
B Width of loading plate
C’α Secondary compression index
Cc Compression index
DS Dry sand
DT Displacement transducer
E Young Modulus
Eu Undrained modulus
Es Modulus of elasticity of the soil under the foundation
e0 Initial void ratio
Gs Specific Gravity
H Thickness of the soil
Is Shape factor
If Depth factor
L Length of loading plate
LL Liquid Limit
PL Plastic Limit
PPT Pore pressure transducer
PT Peat
q Uniformly distributed load per unit area
SPG Soil pressure gauge
Sc Primary settlement
Si Immediate settlement
Ss Secondary compression
St Total settlement
t1, t2 Time
WS Wet sand
xx
LIST OF EQUATIONS
NO. EQUATION PAGE
2.1 St = Si + Sc + Ss 25
2.2 Si = ∆σ (αB′)1−µs
2
EsIsIf 25
2.3 Sc =Cc H
1+e0 log
σ′0+∆σ′
σ′0 27
2.4 Ss = C′αH logt2
t1 28
2.5 dq = q dx dy 30
2.6 ∆σz = 3p
2π
z3
L5 =3P
2π
z3
(r2+z2)5
2 30
2.7 σz = 3q dx dy z3
2π(x2+y2+z2)5
2 31
2.8 ∆σz = dσz = 3qz3(dx dy )
2π(x2+y2+z2)5
2 = qI3
L
x=0
B
y=0 31
2.9 I3 =1
4π
2mn m2+n2+1
m2+n2+m2n2+1
m2+n2+2
m2+n2+1 + tan−1
2mn m 2+n2+1
m2+n2−m2n2+1 31
2.10 m =B
z, n =
L
z 31
2.11 ∆σz = q I3(1) + I3(2) + I3(3) + I3(4) 31
3.1 w =W 2−W 3
W 3−W 1× 100% 58
3.2 Gs =γk m2−m1
m4−m3 − m3−m2 59
3.3 OC =m2−m3
m2−m1× 100% 60
xxi
LIST OF APPENDIX
APPENDIX TITLE PAGE
A Calibration for Displacement Transducers 175
B Calibration for Soil Pressure Gauges 176
C Calibration for Pore Pressure Transducers 178
D Values of Z, B and L 179
E The calculated Stresses Value 180
CHAPTER 1
INTRODUCTION
1.1 Preamble
Peat is a very weak material in its normal (unloaded) state on which to construct a
road/building (Forestry Civil Engineering, 2010). The peat soil is a soft soil with
high compressibility and it is widely identified in Malaysia. The peat soil was
identified as one of the major group in Malaysia. Huat (2004) clarified that the total
area of tropical peat swamps forests or tropical peat land in the world amounts to
about 30 million hectares and some 3.0 million hectares or 8% of the total area of
Malaysia was covered by peat as shown in Figure 1.1. Generally, peat soils occur
both in the highlands and lowlands. However, the highland organic soils are not
extensive. The lowland peat occurs almost entirely in low-lying, poorly drained
depressions or basins in the coastal areas. In Peninsular Malaysia, they are found in
the coastal areas of the east and west coast, especially in the coastal area of West
Johor, Kuantan and Pekan districts, the Rompin- Endau area, northwest Selangor
and the Trans-Perak areas in the Perak Tengah and Hilir Perak districts (Huat,
2004). There are two types of peat deposit, the shallow deposit usually less than 3m
thick while the thickness of deep peat deposit in Malaysia exceeds 5 m (Hashim and
Islam, 2008a).
2
Peat in Malaysia can be categorized as a tropical peat with unique
characteristics. Thus, this makes it significantly different from other peat. In its
natural state, this soil is normally dark reddish brown to black in colour and consists
of partly decomposed leaves, branches, twigs and tree trunks with a low mineral
content (Zainorabidin and Wijeyesekera, 2007). Table 1.1 shows the characteristics
of peat in Malaysia.
Table 1. 1: Characteristics of Peat Swamps in Malaysia (Muttalib, 1991). (Cited by
Zainorabidin and Wijeyesekera, 2007)
Region Location Topography Total Area Characteristics
Peninsular West Johore,
Kuantan, Pekan,
Selangor, Perak.
Peat land is flat. Approximately 80,
000 km2 with 89% of
its 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
Lambang.
The basin peat
swamps are
dome-shaped.
16500 km2
with 89%
of its 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.
Figure 1. 1: The distribution of Peat in Malaysia (Andriesse, 1974)
KALIMANTAN
EAST MALAYSIA
SOUTH CHINA SEA BRUNEI
INDIAN OCEAN
WEST
MALAYSIA
3
Road construction over peat presents great challenges to road builder not
only in the construction process but also in the management of the engineering
properties of peat which have high water content (>200%), high compressibility (0.9
to 1.5), high organic content (>75%) low shear strength (5-20kPa) and low bearing
capacity (<8kN/m2), large deformation and high magnitude and rates of creep
(Zainorabidin and Wijeyesekera, 2007; Haan and Kurse, 2006). This unique
characteristic of peat has led to the problems of the construction become challenging
in Malaysia (Zainorabidin and Bakar, 2003; Hashim and Islam, 2008a).
The peat which was formerly considered unsuitable foundation for the
construction had to be used because of the land use or demand. The challenges faced
by engineers in road/building construction over peat include limited accessibility,
drainage problem and stability problems. Hence, construction process on peat soil
has become more complex. In order to construct a safe, stable and serviceable road,
a road engineer has to overcome this engineering problem by using suitable
solutions to construct roads on peat soil. It is also important for engineers to know
the nature of the distribution of stress along a given cross section of the soil profile
that is, what fraction of the normal stress at a given depth in a soil mass to analyse
the problems such as compressibility of soils, bearing capacity of foundations,
stability of embankment, and lateral pressure on earth-retaining structures (Das,
2011).
1.2 Description of Problems
Peat is considered as a worst soiling foundation compared to other types of soil with
low strength, high permeability and high water content. Zainorabidin and
Wijeyesekera (2007) discussed the geotechnical challenges that need to be faced by
geotechnical engineers in Malaysia during the designing and managing the
construction on peat soil. Among the challenges include the difficulty to get the
4
samples of hemic and fibrous peat using conventional undisturbed samplers and the
different method of sampling for the different depth of peat soil.
Staley (2007) stated that the impact of settlement can be significant,
particularly where the differential settlement occurs due to a peat deposit having
variable thickness, groundwater flow direction, slopes, differential loading or
previous compressions. Because of settlement occurs gradually, it is important to
give more attention on impacts of additional loading and water level against the
settlement. In this study the effect of additional loading was observed and the water
level was maintained.
Ferguson (as cited in Wartman 2006) stated that physical models have served
important functions in engineering research, practice and education for hundreds of
years. In additional, the full scale experiments are very expensive, difficult to run,
and are hard to repeat (Meguid, 2008). Hence, because of this reason, this study
focussed on physical models in the laboratory.
One of the case studies in Malaysia was in Sibu, Sarawak. The peat
formations in some parts of Sibu are well over 10 meters in depth (Vincent, 2009).
Figure 1.2 shows the settlement in a housing area in Sibu town, which cause a
serious problem. This problem caused high risk to occupant in terms of safety.
Duraisamy and Huat (2008) highlighted that ground subsidence on peat generally
resulted in negative gradients to drainage. This scenario resulting of unhealthy water
stagnation in many parts of the town and it is also prone to flooding (Kolay et al,
2011).
Figure 1.2: Settlement in the Housing Area, Sibu, Sarawak (Author, 2009)
5
Figure 1.3 shows the settlement near Salim-Airport Road By-pass, Sibu,
Sarawak. The figure 1.3 (a) shows the gap between the pipeline with the ground
surface and Figure 1.3 (b) show the settlement under a lamp post. According to
Duraisamy and Huat (2008), the problem of this settlement is mainly caused by
either uncontrolled land filling or ground water lowering due to over drainage or due
to both of the activities.
Figure 1.4 was taken during a site investigation in Parit Nipah, Johor, which
is in the housing area. This house has been built on peat soil. The author observed
that the settlement occurred and this can clearly see in the columns that support the
house. It is dangerous to the occupants. The owner needs to place an object like a
rock or wooden block between column and foundation because of some columns
appear hanging as shown in Figure 1.4 (a).
The interaction between structure and foundation is important especially to
distribute the loading of the structure uniformly into the foundation. Sekhar (2002)
stated that the force quantities and the settlement at the finally adjusted condition
can only be obtained through interactive analysis of the soil-structure analysis.
Figure 1.4 (b) shows higher settlement value in the peat. Loading from a small
wooden house have been distributed to the ground and resulted in the settlement.
The settlement in this area was in the range of 150 mm. Peat is not suitable to
support higher loads because of the high compressibility.
(b) (a) Figure 1.3: Settlement for (a) pipeline and (b) lamp post near Salim-Airport Road
By-Pass, Sibu, Sarawak (Author, 2009)
6
1.3 Objectives
The objectives of this study are:
a) To identify the engineering properties of the tested peat,
b) To investigate and analyse the deformation behaviour in peat soil based on
physical modelling,
c) To investigate and analyse using physical model the stress distribution
beneath the structure in peat soil and,
d) To compare and analyse the peat behaviour with sand.
1.4 Scope of Study
Physical modelling is considered as a prime method to study the peat soil – structure
Figure 1.4: Settlement on Peat Soil, Parit Nipah, Johor (Author, 2011) (a) Rock between column and foundation and (b) Settlement Value
(a) (b)
150 mm
Rock
Column
Peat
7
interaction. The purpose of this physical model study is to acquire basic
understanding of the behaviour and stress of peat soil when load is applied to it. This
physical model study has been conducted on peat soils obtained from the Malaysian
Agricultural Research and Development Institute-Integration Peat Research Station
(MARDI-IPRS) in Pontian, Johor. Index properties of peat soil were determined by
conducting site investigation and experiments on disturbed peat obtained from the
site.
Three different sizes of the box for the physical modelling have been used in
this study. The small box with a size 35cm x 2cm x35cm and the square box with
size 30cm x30cm x 30cm have been used in Pre-Model Study (PMS). This PMS is
important because the author can control the variable before implement it into the
Plane Strain Study (PSS) model. For proper monitoring and instrumentations
purpose, the large box with dimensions of 200cm x 50cm x 90cm with a transparent
perspex plate as a wall has been used. Three types of instrumentations have been
used which is displacement transducers (DT), soil pressure gauge (SPG) and pore
pressure transducers (PPT). To minimize friction between soil and the box, plastic
sheeting was attached to the inner sides of the box. Grid paper has been installed in
the outer side of the box for manual monitoring of settlement.
The model has been constructed for sand with the coal and laterite as an
indicator. A constant static load was applied to the peat layer. Then, the model for
the peat soil with sand as an indicator has been constructed. For this test, the
different value of load which is based on the stress increment equal to 2 was applied.
This increment is adapted from the consolidation theory. The various loads have
produced the different stress distribution. The interaction between peat soil and sand
with the structure was recorded based on all the deformations and stresses that
occurred. The water level was maintained at constant level that is at the surface of
the peat. This was done so as to prevent any induce stress due to the seepage of
water and to omit settlement due to the lowering of the water table. Sand has been
used as a comparison to the peat soil by conducting the same testing method for the
peat soil. In this study, priority focuses on the observations in settlement and the
stress distribution. The methodology of this study is summarized as shown in Figure
1.5
8
Figure 1. 5: Flow Chart
INSTALLATIONS (Wrapper, Grid Paper & Label, Sand (filter),
Instrumentations & Data Logger Connection)
PROBLEM IDENTIFICATION (Identify Research Problems, Scope & Objective)
SAMPLE COLLECTION (Disturbed Sample, Von Post of Humification)
DESIGN FOR PLANE STRAIN STUDY
(PSS) (To Identify Numbers of Instruments, Location of
Instruments & load)
SAMPLE PREPARATION (Sieve Peat Sample)
DESIGN FOR PRE-MODEL STUDY (PMS) (To Identify the Types of Indicator, Location of
Indicator)
INSTRUMENTATIONS &
DATA LOGGER PRACTICES (Displacement Transducer (DT), Soil Pressure
Gauge (SPG), Pore Pressure Transducer (PPT)
MAINTENANCE & CALIBRATIONS (Box & Instrumentations)
SOIL IDENTIFICATION (Moisture Content, pH, Specific Gravity, Organic
Content, Unit Weight, LL)
PRE- MODEL STUDY (PMS) (35cm x 2cm x 35cm)& (30cm x30cm x 30cm)
(Check the Failure Indicator, Failure Pattern, Plate
Footing for DT)
PLANE STRAIN STUDY (PSS) (200cm x 50cm x90cm)
(Check Displacement, Stress and Pore Pressure)
SAND
PEAT
DRY SAND
WET SAND
PEAT RESULTS & ANALYSIS
CONCLUSIONS & RECOMMENDATIONS
9
1.5 Importance and Contribution of Study
Currently, the study of physical modelling sees an increasing use in geotechnical
engineering (Wartman, 2006). The finding from this study can give benefit to
engineers, contractor, academician and other in this area for better understanding on
the concept of settlement on peat soils. Physical models can clearly portray the
geotechnical mechanism and also the phenomena that are difficult to visualize
(Wartman, 2006). The physical model study generally used as complements to the
laboratory testing. This physical model is important because it can test the theory or
the process before implement it into the full scale test.
1.6 Organization of Thesis
This thesis consists of seven chapters including the first introductory chapter. The
contents of the chapters are as summarized below:
(1) Chapter 1: Introduction
This chapter presented the proposal of this study that included problem
statements, objectives, scope of study and the contribution of this study. The
author has included some of the settlement problems occurred in Malaysia
especially in Johor and Sarawak.
(2) Chapter 2: Literature Review
This chapter listed the necessary literature review from the past researchers
related to this study. The relevant information of peat and sand were
described in order to get better understanding based on their behaviour. The
interaction between structure (load) – soil and the challenges in peat were
also listed. This chapter also reviewed and summarized the histories for the
physical modelling and full scale testing on peat.
10
(3) Chapter 3: Sample Preparation
This chapter described the location of peat soil used in this study. The
method to produce the uniform sample also elaborated in this chapter. The
author identified the physical properties of Pontian peat soil by conducting
the von post scale humification, moisture content, specific gravity, organic
content and pH. Hence, the methods used and the results obtained were
described in the last parts of this chapter.
(4) Chapter 4: Pre-Model Study (PMS)
This chapter presented the methods of construction the pre-model study
included the model design. This PMS is used to identify the suitable
indicator to detect the deformation behaviour in peat and sand. Four
materials (coal, laterite, sand and polystyrene) have been tested its
effectiveness as an indicator and the results obtained are also included in this
chapter.
(5) Chapter 5: Plane Strain Study (PSS)
This chapter consists of the procedure in the plane strain study. The PSS was
used with advanced instrumentations such as displacement transducers, soil
pressure gauges and pore pressure transducers to investigate and observed
the settlement, stress and pore pressure in peat and sand. The installation of
displacement transducers, soil pressure gauges and pore pressure transducers
were also discussed including information towards the calibration for each
instrument. The model design, model construction, model testing and the
results obtained based on these tests were elaborated in this chapter.
(6) Chapter 6: Results and Analysis
The data obtained from the PSS then were analysed. Three types of
measurements that have been collected which are settlements, stresses and
pore pressures. The analysis and early conclusion were discussed in this
chapter.
(7) Chapter 7: Conclusions
This chapter provided the summary of the results and recommendations.
11
1.7 Tests Schedule
The schedule of the test conducted in this study is as shown in Table 3.1.
Table 1.2: Schedule of Tests Conducted
Types Experiments Remarks
INDEX
PROPERTIES
TEST
(1) Von Post Scale of Humification
(2) Moisture Content
(3) Specific Gravity
(4) Organic Content
(5) pH
(6) Unit Weight for Sand/Peat
(7) Liquid Limit
These testings
have been
conducted using
the samples that
pass sieve 25mm
x 8mm.
PRE-MODEL
STUDY
(PMS)
(1) INDICATOR FOR SAND
(a) Rectangular Model: Identify the suitable
indicator using coal and laterite.
(b) Square Model: Identify the suitable indicator
using coal and laterite.
Small and square
models were used
to observe the
suitable indicator
and the
deformation
pattern of the soil
after loads were
imposed on it.
(2) INDICATOR FOR PEAT
(a) Rectangular Model: Identify the suitable
indicator using polystyrene and sand.
(b) Square Model: Tests for Polystyrene and sand,
comparison test for indicators and test in finding
the best placing method of the indicator.
(c) Beaker: Identify the sand sizes for indicator,
comparison test between indicators.
(3) DEFORMATION PATTERN
Observed from the tests of finding the suitable indicator
for sand and peat.
(4) PLATE SIZE FOR DT
PLANE
STRAIN
STUDY (PSS)
(1) DRY SAND (DS)
Using Plane Strain Study Model
The larger
instrumented
model was used
with advanced
instrumentations
(DT, SPG, PPT)
to observe the
settlement, stress
and pore pressure
of the soil.
(2) WET SAND (WS)
Using Plane Strain Study Model
(3) PEAT (PT)
Using Plane Strain Study Model
12
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Soil composed of a varying ratio of mineral, air, water and organic material. It is
consists about 40% mineral, 23% water, 23% air, 6% organic material and 8% living
organisms. There are many types of problematic soil. Some of the most noteworthy
being swelling or shrinking clay, collapsible soils, frozen soils and peat (Culshaw,
2001).
United Nations Economic and Social Commission for Asia and the Pacific
(ESCAP) secretariat (1989) and Jali and Choudry (1992) cited in Leong and Chin
(2000) that lack of study on the geotechnical characteristics of peaty soil deposits in
Southeast Asia despite the fact that peaty soil deposits are recognized to cause
serious geotechnical engineering problems. As in Malaysia, the utilization of peat
land is quite low although the construction of this type of soil has become
increasingly necessary for economic reasons and also to support the increasing
population in Malaysia. Engineers are reluctant to construct a road or buildings on
peat because of difficulties to access the site and also the challenges in the
management of the engineering properties of peat. The challenging soil with high
compressibility and low shear strength often result in difficulties for the construction
works. The low strength in peat causes the stability problems and the load applied is
limited. Large deformation may occur during and after construction period in both
vertically and horizontally (Gofar, 2006).
13
This chapter starts with the introduction to the peat and sand which is
covered about the properties of the soils itself. Then the review based on the
behaviour of peat and sand under static loading was highlighted. This behaviour was
including the settlements, stresses and pore water pressures. In this chapter also
consists of the challenges of peat, the failure pattern, the case studies and also the
indicators of the failure that have been used by the past researchers. The literature
review is divided into several parts as shown in Figure 2.1.
2.2 Peat Soil
2.2.1 Definition of Peat
According to ASTM D4427-92 (1997), peat is defined as soil that naturally
occurring with highly organic substance derived primarily from plant materials. It is
Introduction
Peat
Sand
Behaviour of Soil under Static Loading
(Settlements, Stresses & Pore water Pressure)
Failure Pattern
Case Studies
Figure 2.1: Summary of Literature Review
Challenges of Peat
Indicator for Failure Pattern
14
formed when organic (usually plant) matter accumulates more quickly than it
humidifies (decays). This usually occurs when organic matter is preserved below
high water table like in swamps or wetlands (Duraisamy and Huat, 2008). The rate
of peat accumulation varies in different places depending on the bog plants live and
die on the surface (Leong and Chin, 2000).
Geotechnical engineers define peat as soils that organic content is more than
75% and the soil with organic content below 75% was categorized as organic soils.
However, in soil sciences, the soils that have an organic content more than 35% are
classified as peat. The definitions for peat soil can be summarized as in Table 2.1.
Table 2. 1: Different Descriptions of Peat (Zainorabidin, 2010)
Field Description Standard
Geotechnical
engineering
All soils with organic content greater than 75% are known as
peat. Soils that have an organic content below 75% are
known as organic soils.
ASTM D4427-
1997
Soil science
All soils with organic content greater than 35% are
categorized as peat.
USDA (Soil
Taxonomy)
2.2.2 Classification
Soil classification is important in engineering to describe the properties, texture and
grain size of a soil. It is necessary to adopt a formal system of soil description and
classification to describe the materials found in ground investigation. The
classification also can be made based on the observation on the structure of the
system itself. Under the soil classification system, peat was included under the name
of muck soil, bog soil and organic soil (Montanarella, 2006).
In soil classification system, peat can be classified into three distinguish
degrees of decomposition which are fibric, hemic and sapric. The classification is
based on the fibre content in peat as shown in Table 2.2. For the peat with fibre
content more than 66%, it is classified as Fibric. For 33% to 66% fibre content, this
15
can be categorized as hemic and for fibre content less than 33%, can be classified as
Sapric.
Table 2. 2: Classification of Peat
Classification Fibre Content Degree of Von Post Humification
Fibric > 66% H4 – less
Hemic 33% - 66% H5 – H6
Sapric <33% H7
Fibric peat will cause highest settlements followed by hemic and sapric when
subjected to any load over the time period (Duraisamy et al, 2007). Figure 2.2 shows
the compression index (Cc) values of Rowe Cell consolidation test for fibric, hemic
and sapric peat. Cc for fibric peat was within the range of 1.878 to 3.627, for hemic
peat was recorded as 1.34 to 2.99 and sapric peat was 1.24 to 2.63.
Figure 2. 2: Compression Index versus Consolidation Pressure (Duraisamy et al,
2007)
There are two methods that were used to classify peat in Canada; the
Radforth classification and Von Post Classification. The Radforth system is based
on the visible structure with the engineering properties estimated from this structure.
16
This system has only been adopted in Canada (Hobbs 1986). Radforth (1969) stated
that peat is considered to fall into three main groups for engineering purposes which
are amorphous granular peat, fine fibrous peat and course fibrous peat. The
amorphous granular peat consists of peat with a high colloidal mineral component
which tends to hold the contained water in an adsorbed state around the grain
structure. The two fibrous peat types, „fine-fibrous‟ and „coarse-fibrous‟, are
woodier and hold most of their water within the peat mass as free water.
Hendry (2011) stated that the von Post system is a more extensive
classification method and forms the basis for the American Society for Testing and
Materials (ASTM) standards for the classification and testing of peat and organic
soils. The von Post system shows strong correlations of classification of the physical
peat properties to the engineering properties. These physical properties include: the
extent of humification (decay of plant matter) (ASTM D5715), the predominant
plant, the content of fibres (ASTM D1997), the classification of bulk unit
weight/density (ASTM D4531), water content (ASTM D2974), specific gravity
(ASTM D854), pH (ASTM D2976), Atterberg limits (ASTM D4318) ( Hendry,
2011). The Atterberg limit is not applicable to all types of peat because liquid limit
and plastic limits cannot be determined for the more fibrous peats (Hobbs 1986).
In this study, the classification of peat is based on the Von Post system. Von
Post and Granlund (1926) cited in Long (2005) that the best known classification
system for peat is von post scale. It is based on the categorization of botanical
composition, degree of humification, water content, fibre content (fine and coarse)
and content of woody remnants. Degree of humification can be obtained by
conducting Von Post Squeeze Test and it is obtained on a scale H1 (completely
unhumified fibrous peat) to H10 (completely amorphous non fibrous peat) as shown
in Table 2.3.
17
Table 2. 3: The Von Post Scale of Humification (Von and Granlund, 1926)
Degree of
Humification
Decomposition Plant
Structure
Content of
amorphous
material
Material
extruded on
squeezing
(passing
between
fingers)
Nature of
residue
H1
None
Easily
identified
None
Clear,
colourless
water
-
H2
Insignificant Easily
identified
None Yellowish
water
-
H3
Very slight Still
identifiable
Slight Brown, muddy
water; no peat
No pasty
H4
Slight Not easily
identified
Some Dark brown,
muddy water;
no peat
Somewhat
pasty
H5
Moderate Recognizable,
but vague
Considerable Muddy water
and some peat
Strongly pasty
H6
Moderately
strong
Indistinct
(more distinct
after
squeezing)
Considerable About one
third of peat
squeezed out;
water dark
brown
Fibres and
roots more
resistant to
decomposition
H7
Strong Faintly
recognizable
High About one half
of peat
squeezed out;
any water very
dark brown
H8
Very strong Very indistinct High About two
thirds of peat
squeezed out
also some
pasty water
H9
Nearly
complete
Almost
unrecognizable
- Nearly all the
peat squeezed
out as a fairly
uniform paste
-
H10
Complete
No discernible - All the peat
passes between
the fingers; no
free water
visible
-
18
2.2.3 Peat Characteristics and Properties
The high annual rainfall and poor drainage are the conditions of peat formation
(Leong and Chin, 2000). Peat deposit generally exists at high natural water content
and void ratio. This peat soil deposit at high void ratios because plant matters that
constitute peat particle are light and hold a considerable amount of water. The
specific gravity of peat is relatively small. Hence, it makes the peat grains, plates,
fibres or element is light and the particle of peat is porous (Mesri et al., 1997).
Craig (1992) mentioned that the colour of peat usually dark brown or black
and with a distinctive odour. The main component of the peat itself is organic matter
(Whitlow, 2001). Hence, peat poses many problems because of it is very spongy,
highly compressible and combustible in characteristic. This characteristic also made
the peat pose its own distinctive geotechnical properties compared with other
inorganic soils which are made up by the soil particle only (Deboucha et al., 2008).
Kazemian et al. (2011) also highlighted that the fresher the peat, the more fibrous
material contains.
The unique characteristics of peat have led to the problems of the
construction (Hashim and Islam, 2008a). Melling (2009) stated that peat is one of
the softest and problematic soils and it is subjected to instability and massive
primary and long-term consolidation settlements. Huat (2004) stated that peat are
commonly occurring as extremely soft, wet unconsolidated surficial deposits that are
integral parts of the wetland systems. This peat soil also has the mechanical
behaviour which is different from the other mineral soils such as clay which is high
porosity, extremely compressible, strong dependence on permeability and porosity,
large change in properties under stress, high degree or spatial variability in
properties, fibrosity and high strength due to fibre reinforcement. Hence, peat is
considered unsuitable for supporting the foundation in its natural state (Hashim and
Islam, 2008a). The content of peat soil varies from location to location due to the
factor such as origin fibre, temperature and humidity (Huat et al, 2009).
The properties of peat are greatly dependent on the formation of its deposits
and the organic content. This proves that, peat at different locations usually has
19
different properties. Noto (1991) explained that peat has extremely high water
content and the wet density of peat approximates the density of water, as the main
constituent of peat is dead vegetable matter.
Hobbs (1986) and Edil (1997) as cited in Huat (2004) states that the physical
characteristics such as colour, degree of humification, water content and organic
content should be included in a full description of peat. The physical properties of
peat are influenced by main component of its formation such as organic content,
moisture and air. When one of these component changes, it will result in the changes
of the whole physical properties of the peat soil. Table 2.4 shows the index
properties for peat.
Table 2. 4: Index Properties of Peat (Munro, 2004)
Index Properties Descriptions
Ash content
The ash content is the percentage of dry material that remains as ash after
controlling combustion.
On the west coast of Peninsular Malaysia, the ash content of the peat is less than
10%, showing a very high content of organic matter. (Hanzawa et. al, 1994).
Bulk density Bulk density of peats is affected by the structure and degree of humification.
At the top 30 cm of the peat, the bulk density of the peat in Peninsular Malaysia
is low and varies from 0.1 to 0.2g cm-3
.
Dry density Depend on the natural moisture content and mineral content of the particular
deposit.
Important characteristics for engineer concerned with road construction over
peat as it influences the behaviour of the peat under load.
Colour The colour of peat ranges of light-yellow to yellowish, reddish and dark brown
to dense black.
The colour of peat also indicates the degree of decomposition.
Degree of
humification
Indicates the degree to which the organic content has decayed.
Moisture content Moisture content of peat ranges from 100 to 1300 % on a dry basis.
The moisture content of peat is affected by the origin, degree of decomposition
and chemical component of peat. Hanzawa et.al (1994), states that the natural
water content of some peat could exceed 1000%.
Organic content Organic content is an indicator of peat purification from any mineral
component.
The measurement is from any mineral component and important to classify the
peat.
Void ratio Void ratio of peat varies with the type of peat and moisture content.
For fibrous peat the void ratio as high as 25 and for the denser amorphous
granular peats is as low as 9.
Permeability Permeability of peat at site is highly variable depending on its morphology and
reduces dramatically when subjected to loading.
Shear strength Depends on its moisture content, degree of humification and mineral content.
- The higher the moisture contents of the peat, the lower its shear
strength.
- The higher the degree of humification and mineral content of the peat,
the higher its shear strength.
20
The water content of peat researched in West Malaysia ranges from 200 to
700 % (Huat et al. 2004). Zainorabidin and Ismail (2003) highlighted that for peat in
Johore, the water content can reach up to 500% with the unit weight ranges from 7.5
to 10.2 kN/m3. Unit weight of the peat is typically lower compared to inorganic
soils. A range of 8.3 – 11.5kN/m3 is common for a unit weight of fibrous peat in
West Malaysia. The organic content in the range of 65 % to 97 % and the Atterberg
limit was in the range of 200 % to 500 % as reported by Huat (2004). The detail of
the properties of peat soil in Malaysia is as summarized in Table 2.5.
Table 2. 5: Properties of Peat Soil in Malaysia
Soil Deposit West Malaysia Peat
and Organic Soil
East Malaysia Peat
and Organic Soil
Johore Hemic Peat
Natural Water Content,
w (%)
200-700 200-2207 230 – 500
Liquid Limit, LL (%) 190-360 210-550 220- 250
Plastic Limit, PL (%) 100-200 125-297 -
Plasticity Index, PI (%) 90-160 85-297 -
Specific Gravity, (Gs) 1.38-1.70 1.07 – 1.63 1.48 – 1.8
Organic Content (%) 65-97 50-95 80 -96
Unit Weight (kN/m3) 8.3 – 11.5 8.0-12.0 7.5 – 10.2
Undrained Shear
Strength (kPa)
8-17 8.0 – 10.0 7- 11
Compression Index, Cc 1.0-2.6 0.5-2.5 0.9 – 1.5
Refs. Huat (2004) Huat (2004) Zainorabidin and
Ismail (2003)
2.3 Sand
2.3.1 Definition and Formation
Sand is a naturally occurring granular material composed of finely divided rock and
mineral particles. It is highly variable and depending on the local rock sources and
conditions. The most common constituent of sand is silica, usually in the form of
quartz and also calcium carbonate like aragonite.
21
2.3.2 Classification and characterization
Sand classification was based on two major groups which is coarse and fine. Sand is
classified as coarse sand because having particle sizes >0.06 mm. Their grains will
be rounded or angular and usually consists of fragments of rock or quartz or jasper,
with iron oxide, calcite, and mica often present.
The British Soil Classification System (BSCS), in BS 5930: 1981 states that
sand particles are between 0.06 mm to 2 mm. Unified Soil Classification System
(USCS) under ASTM D2487, the grain size of sand would be in the range of 75µm
to 4.75µm. The sand feels gritty when rubbed between the fingers. Table 2.6 shows
the relationship between the USCS and the BSCS classification system.
Table 2. 6: Soil Classification System
Sand has small surface areas and has an almost negligible role in the
chemical activity of the soil. The sand acts as the framework for the active particles
and does not hold much water because the particles act as single grains. In soil the
sand particles affect the size of voids. They tend to increase the size of the voids
22
allowing free movement of water and air. Therefore, sandy soils are well drained
and well aerated.
Terzaghi (1925) stated that sand has a volume of voids about 50 percent of
the total volume, did not shrink in drying, has negligible cohesion when clean, not
plastic and compress almost immediately when load is applied to the surface.
2.4 Behaviour of Soil under Static Loading
2.4.1 Settlements
The load–deformation relationship for soil is usually complex and varies widely
with different soil. This settlement problem plagued engineers and builders for a
long time. For example, the tower of Pisa and some structures in Mexico City as the
Palace of Fine Arts and the Tower of Latino Americana are known not because of
their architectural features but rather for the obvious effect of the settlement. The
settlement damages are still occurring, and it has become a continuing challenge to
the geotechnical engineers (Cernica, 1995). This load-deformation behaviour is
dependent on the interaction between the structure and the soil on which it is
founded (Mangal, 1999). Most of the engineering structure was direct contacted with
the ground. The process in which the response of the soil influences the motion of
the structure and the motion of the structure influences the response of the soil is
termed as soil-structure interaction (SSI).
2.4.1.1 General
Structures built on the soil are subject to the settlement. The settlement refers to the
vertical downward displacement at the base of a foundation or other structure due to
23
ground movement (Whitlow, 2001). Whitlow (2001) stated that there are several
possible causes of settlement which are:
(a) Static loads which are imposed by the weight of a structure or an
embankment.
(b) Dynamic or transient loads which are produced by machinery or moving
loads on roads or airfield pavements, pile driving, blasting, etc.
(c) Changes in moisture content, for example from seasonal fluctuations in the
water table.
(d) Rainfall and evaporation or the absorption of the water by the roots or larger
trees.
(e) The effect of nearby construction such as excavation, pile driving,
subsidence of mines and dewatering may also be significant.
(f) Ground movement on earth slopes such as erosion, landslide or slow creep.
Cheng (1998) cited that although there are several possible causes of
settlement, probably the major causes are compressive deformation of soil beneath a
structure. This compressive deformation generally results from the reduction in void
volume, accompanied by rearrangement of soil grains and compression of the
material in the voids. For the dry soil, it voids are filled with air that is compressible.
So, the rearrangement of soil grains can occur rapidly. In the saturated soil, its voids
are filled with incompressible water. This water must be extruded from the soil mass
before soil grains can rearrange themselves. In soil of high permeability (coarse
grained soil), the process requires a short time interval for completion and settlement
occurs by the time of construction is complete. In soil with low permeability (fine
grained soil), the process requires a long time interval for completion and resulted in
settlement occurring very slowly.
For soil, the load – deformation relationship is usually complex, varying
widely with different soils and particularly in the plastic range of cohesive soils,
where time plays a major role. The settlement increases in magnitude with an
increase in load, although not linearly (Cernica, 1995). Settlement is the direct result
of reduction of volume of a mass. This reduction could be attributed to the following
factors:
(a) The escape of water and air from the voids
24
(b) Compression of the soil particles
(c) Compression of air within the voids.
Surface loading results in under soil stresses in horizontal and vertical
direction. Consolidation also occurs in both the horizontal and the vertical direction.
But, the vertical compression or consolidation is the largest, and it is the most
important component (Cernica, 1995).
Kazemian et al., (2011) stated that the compressibility of soil generally
consists of three stages namely initial compression, primary settlement, and
secondary compression. The total settlement of a foundation can be given as:
St = Si + Sc + Ss (2.1)
where, St = expected total settlement
Si = immediate settlement
Sc = primary settlement
Ss = secondary compression
2.4.1.2 Sand
The immediate settlement or elastic settlement occurs during a fill or a structural
loading. It is caused by a static load and occurs essentially at the same time as these
loads are applied to the soil (Brennon, 2007). Kazemian et al. (2011) mentioned that
this immediate settlement occurs in all types of soil and mainly due the compression
of gas within the pore spaces and the elastic compression of soil grains. This
immediate settlement is important to granular soil. The settlement may be expressed
as:
Si = ∆σ (αB′)1−µs
2
EsIsIf (2.2)
168
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