DEVELOPMENT OF SOIL-EPS MIXES FOR GEOTECHNICAL APPLICATIONS HEMA KUMAR ILLURI A thesis submitted for the degree of Doctor of Philosophy School of Urban Development Centre for Built Environment and Engineering Research Queensland University of Technology, Australia 2007
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DEVELOPMENT OF SOIL-EPS MIXES FOR
GEOTECHNICAL APPLICATIONS
HEMA KUMAR ILLURI
A thesis submitted for the degree of
Doctor of Philosophy
School of Urban Development
Centre for Built Environment and Engineering Research
Queensland University of Technology, Australia
2007
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To my parents,
(late) Illuri Harinatha Babu Rao and
Illuri Hymavathy.
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STATEMENT OF ORIGINAL AUTHORSHIP The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institute. To the
best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.
Signed: _________________________________
Hema Kumar Illuri
Date: ___________________________________
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CONTENTS
Statement of original authorship v Abstract xi Acknowledgements xiii List of Figures xv List of Tables xxv Nomenclature xxvii List of publications xxix
CHAPTER 1 INTRODUCTION 1 1.1 Background 1 1.2 Hypothesis and focus of the research 5 1.3 Objectives of the research 6 1.4 Organisation of the thesis 7 CHAPTER 2 EXPANDED POLYSTYRENE AND ITS UTILISATION 9 2.1 Expanded polystyrene 9 2.2 General uses and properties of EPS 11 2.3 Applications of EPS in geotechnical engineering 13 2.4 Soil-EPS mixes as lightweight fill materials 17 2.5 EPS applications in Australia 30 2.6 Management of waste EPS 32 2.7 Summary 36 CHAPTER 3 EXPANSIVE SOILS AND THEIR TREATMENTS 39 3.1 Expansive soils 39 3.2 Factors influencing mechanisms in expansive soils 40 3.3 Distribution of expansive soils in Australia 43 3.4 Characteristics of expansive soils 44 3.5 Effects of expansive soils on different structures 46 3.6 Expansive soil treatment options 48 3.7 Possible use of soil mixed with EPS beads 61 3.7 Summary 63 CHAPTER 4 SCOPING STUDIES WITH A DREDGED SOIL 65 4.1 Dredged soils 65 4.2 Waste EPS 68 4.3 Dredged soil from Port of Brisbane 72 4.4 Preparation of dredged soil and EPS mix 73 4.5 Optimum mix proportion of soil-EPS mixes 74 4.6 Compaction properties of soil-EPS mixes 76 4.7 Strength behaviour of soil-EPS mixes 80 4.8 Swell-shrink studies 88 4.9 Need for further studies with reconstituted expansive soils 91 4.10 Summary 92
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CHAPTER 5 SAND-BENTONITE (SB) MIXES 93 5.1 SB mix as a model material for expansive soil 93 5.2 Material properties 97
5.3 SB mix preparation 99 5.4 Atterberg limits 99
5.5 Hygroscopic moisture content 103 5.6 Compaction behaviour 104 5.7 Optimum lime content 107 5.8 Preparation of Soil with EPS (SWEPS) mixes 110 5.9 Specific gravity of SWEPS mixes 111 5.10 Summary 112
CHAPTER 6 COMPACTION OF SOIL WITH EPS (SWEPS) MIXES 113 6.1 Compaction studies 113 6.2 Experimental programme 114 6.3 Compaction curves 116 6.4 Effects of EPS on maximum dry unit weight 119 6.5 Effects of EPS on optimum moisture content 121 6.6 Effect of degree of compaction 122 6.7 Comparison of compaction characteristics of SWEPS mixes with other composite soils 122
6.8 Volumetric proportions 124 6.9 Predictive model for dry unit weight 127 6.9 Summary 128
CHAPTER 7 SWELLING AND SHRINKAGE STUDIES ON
SWEPS MIXES 131 7.1 Compaction of SWEPS specimens 131
7.2 Swelling characteristics of SWEPS mixes 132 7.3 Cyclic swelling 155 7.4 Effect of EPS and lime on swelling 161
7.5 Shrinkage characteristics 164 7.6 Summary 174 CHAPTER 8 SHEAR STRENGTH OF SWEPS MIXES 177 8.1 Direct shear tests 177 8.2 Unconsolidated-Undrained triaxial tests 197 8.3 Effect of lime on the shear strength of SWEPS mixes 228 8.4 Summary 232 CHAPTER 9 SUCTION AND DESICCATION STUDIES 235 9.1 Suction studies 235 9.2 Desiccation studies 246 9.3 Summary 268
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CHAPTER 10 HYDRAULIC CONDUCTIVITY, COMPRESSIBILITY AND WATER BALANCE ANALYSIS OF A SWEPS MIX 269 10.1 Hydraulic conductivity 269 10.2 Compressibility characteristics 273 10.3 Water balance analysis using Visual HELP software 279 10.4 Summary 290 CHAPTER 11 CONCLUSIONS AND RECOMMENDATIONS 291 11.1 Scientific contribution from this research 291 11.2 Engineering applications 292 11.3 SWEPS mix deign criteria 294 11.4 Conclusions from this research 296 11.3 Recommendations for further studies 298
REFERENCES 301 APPENDIX 327
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ABSTRACT Global concern about the environmental impacts of waste disposal and stringent implementation of environmental laws lead to numerous research on recycled materials. Increased awareness about the inherent engineering values of waste materials, lack of landfill sites and strong demand for construction materials have encouraged research on composite materials, which are either fully or partly made of recycled materials. This trend is particularly strong in transportation and geotechnical projects, where huge quantities of raw materials are normally consumed.
Owing to the low mass-to-volume ratio, disposal of Expanded Polystyrene (EPS) is a major problem. In addition, EPS recycling methods are expensive, labour intensive and energy demanding. Hence, this thesis is focused on the development of a new soil composite made by mixing recycled EPS with expansive clays. Given the high cost of damage to various buildings, structures and pavements caused by the unpredictable ground movements associated with expansive soils, it has been considered prudent to try and develop a new method of soil modification using recycled EPS beads as a swell-shrink modifier and desiccation crack controller. The innovative application of recycled EPS as a soil modifier will minimise the quantity of waste EPS destined to the landfill considerably.
An extensive experimental investigation has been carried out using laboratory reconstituted expansive soils - to represent varied plasticity indices - consisting of fine sand and sodium bentonite. Three soils notated as SB16, SB24 and SB32 representing 16%, 24% and 32% of bentonite contents respectively were tested with four EPS contents of 0.0%, 0.3%, 0.6% and 0.9%. The tests performed include compaction, free swell, swell pressure, shrinkage, desiccation, shear strength and hydraulic conductivity. All the tests have been performed at the respective maximum dry unit weight and optimum moisture content of the mixes. It has been observed that by mixing of recycled EPS beads with the reconstituted soil, a lightweight geomaterial is produced with improved engineering properties in terms of dry unit weight, swelling, shrinkage and desiccation.
The EPS addition depends on the moulding moisture content of the soil. With increasing moisture content, additional EPS can be added. Also, there is a reduction in dry unit weight with the addition of EPS. Furthermore, the reduction of swell-shrink potential and desiccation cracking in soils, for example, is related to the partial replacement of soil particles as well as the elasticity of the EPS beads. There is a reduction in shear strength with the addition of EPS to soils. However, mixing of chemical stabilisers along with EPS can enhance the strength in addition to improved overall properties.
ACKNOWLEDGEMENTS The work described in this thesis was made possible by the award of an Australian International Postgraduate Research Scholarship (IPRS) administered by Queensland University of Technology (QUT), Brisbane, which is gratefully acknowledged.
During the course of Ph.D., the author is privileged to have encouragement, support and patience of many people and organisations inside and outside of QUT and wishes to express his heartfelt thanks to all of them.
In the first instance, the author is glad to take this opportunity to express his profound sense of gratitude and indebtedness to his perspicacious principal supervisor, Dr. Andreas Nata-atmadaja, for his enthusiastic and expert guidance, continuous help, valuable assistance, encouragement, constructive suggestions and positive criticisms throughout the course of this work. His immense patience and availability for comments whenever approached, even amidst his heavy pressure of work throughout the entire period of this research, deserves grateful appreciation. The author falls short of words while paying gratitude to him for his patience in checking the thesis draft.
The author also wishes to express his sincere thanks to Dr. Les Dawes for kindly agreeing to serve as associate supervisor and also for his valuable advice and assistance. Special thanks are extended to Dr. Jon Bunker and Assoc. Prof. Kunle Oloyede for their advice and suggestions.
Sincere thanks are extended to Prof. Mahen Mahendran for providing guidance, assistance and suggestions, in the initial phases without which I have missed this opportunity of pursuing Ph.D. at QUT and also for financial support during the course of the work. Special thanks are extended to Assoc. Prof. Ashantha Goonetilleke, Prof. Luis Ferreira and Prof. David Thambiratnam, for their generous financial support for attending the conferences and for their help and valuable suggestions.
The authour is grateful to the School of Urban Development (and the former School Civil Engineering), Centre for Built Environment and Engineering Research (CBEER) in the Faculty of Built Environment and Engineering at QUT for providing a stimulating environment for research. Moreover, the financial support provided as living allowance throughout the candidature by CBEER, especially Prof. John Bell, is also duly acknowledged.
The Expanded Polystyrene (EPS) was supplied by Queensland EPS recycling centre. The author wishes to express his thanks to Mr. Leo Sines for his help in this regards.
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Special thanks are also extended to Mr. Trevor Laimer, Mr. Arthur Powell and Mr. Terry Beach, for their technical assistance during the course of experiments in this research.
It is pleasure to thank fellow post-graduate students and friends for their support and contribution to this research, especially special thanks are extended to Dr. Prasad Gudimetla, for his comments which enhanced the thesis, Mr. P. Praveen, for his help in extracting the cracking areas using MATLAB®, Mr. Reddy and Mr. Sivaram for their constant support and help during the course of this research. Further, the author extends his profound thanks to Mrs. Lynda Lawson, for her generous help in thesis correction.
A very special vote of thanks goes to Chancellor G. Viswanathan, Vice-Chancellor, Dr. P. Radhakrishnan, and Dr. D.V.S. Bhagavanulu of VIT University, Vellore, India and Dr.U.Lazar John, Principal, Jyothi Engineering College, for their constant support and encouragement extended to the author for pursuing Ph.D. at QUT.
The author would like to acknowledge the contribution of his family, especially his beloved mother, Mrs. I. Hymavathy, for her sacrifices and prayers. Further, special thanks are due to the authors’ father-in-law, Mr. Ch. Rambabu, and mother-in-law, Mrs. Ch. Santha Kumari for their wishes and blessings.
Finally the author expresses his deepest gratitude to his wife Sunitha, for her forbearance, for providing unswerving support, encouragement and tremendous help with cheerful smile during the time spent in this work. Also he is grateful to his son Karthick for his endurance and understanding.
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LIST OF FIGURES Figure Title Page 1.1 EPS packaging products 2
2.1 Generalised diagram for EPS geofoam embankment 14
2.2 EPS being placed over soft ground 15
2.3 Placement of lightweight fill 15
2.4 Construction process for port and harbour structures 19
2.5 On-site mixing process (a) Mixing of EPS beads and stabiliser
and (b) Mixing machine 20
2.6 Central mixing plant (a) Plant mix method and (b) Sealed
batch type mixing plant 21
2.7 Relationship between wet unit weight and mixture ratio of
EPS beads 23
2.8 Sections of caissons and testing cases 23
2.9 Wet unit weight of Soil-EPS composite immediately after placing 24
2.10 Change in wet density after one year 25
2.11 Change in apparent unit weight with mixing rate of beads 25
2.12 Relationship between the wet density and UCS 26
2.13 Unconfined compressive strength with depth 27
2.14 Stress-strain curves for a dredged soil mixed with EPS beads
at a moisture content of 2.5 times liquid limit 28
2.15 Stress-strain curves for the Araike bay mud at liquid limit 29
2.16 Stress- strain curves for the sand mixed with EPS beads with
moisture content 10% above the optimum moisture content 29
3.1 Distribution of expansive soils in Australia 43
3.2 Shrinkage and cracking of expansive soils 44
3.3 Wetting and loss of strength in expansive soils 45
3.4 Relationship between swelling pressure and clay content at
same initial moisture content 53
3.5 Relationship between swell and square root of time for different
stiffnesses at surcharge of 7 kPa. 54
3.6 Variation of swelling strain with fibre dosages on wet and dry of
optimums 56
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Figure Title Page
3.7 Volumetric swell strain of fibre treated soil compacted at 100% of
dry unit weight 57
3.8 Variation of crack sizes and distribution with and without fibres 58
3.9 Crack rduction wih various fibre contents 59
3.10 Variation in swelling with tire chips 60
3.11 Retaining wall backfill treatment 62
4.1 Produce boxes (a) before crushing and (b) after crushing 69
4.2 Size and shape of the EPS beads (a) pre-puff beads and
(b) recycled beads 70
4.3 Particle size distribution curve recycled EPS pieces 70
4.4 Reduction in size of specimens before and after heating at 80° C 72
4.5 Compaction curves for the dredged soil tested 72
4.6 Dredged soil – EPS beads composite before compaction at
45% moisture content 74
4.7 Cross section of Soil-EPS mix at OMC (39%) (a) 0.5% EPS,
(b) 1.0% EPS and (c) 1.25% EPS 75
4.8 Cross section of Soil-EPS mix at 45% water content (a) 1% EPS
and (b) 2% EPS 76
4.9 Cross section of Soil-EPS mix at 50% water content (a) 1% EPS,
(b) 2% EPS and (c) 3% EPS 76
4.10 Variation of wet unit weight with EPS at OMC
(moisture content = 39%) 78
4.11 Variation of wet unit weight with EPS at 45% moisture content 79
4.12 Variation of wet unit weight with EPS at 50% moisture content 79
4.13 Variation of wet unit weight with EPS and initial moisture content 80
4.14 Unsoaked CBR curves 82
4.15 Soaked CBR curves 83
4.16 Stress-strain curve of a composite with 3% lime 85
4.17 Stress –strain curve of a composite with 5% lime 85
4.18 Stress – strain curve of a composite with 7% lime 86
4.19 Typical shear box test on Soil-EPS composite at different
normal stress levels 87
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Figure Title Page
4.20 Vertical displacement of the Soil-EPS composite in shear box test at
different normal stress levels 87
4.21 Shear strength of Soil-EPS composite 88
5.1 Variation of plasticity index at different locations of the world 96
5.2 Particle size distribution curve for sand 97
5.3 X-ray diffraction plot of the bentonite used in the study 99
5.4 Liquid limits and plastic limits for sand bentonite mixes 100
5.5 Variation of plasticity index with bentonite content 101
5.6 Plasticity chart for the sand-bentonite mixtures 102
5.7 Expansion potential of sand-bentonite mixes as predicted by
the chart of Williams and Donaldson (1980) 103
5.8 Compaction curve for SB16 104
5.9 Compaction curve for SB24 105
5.10 Compaction curve for SB32 105
5.11 Variation of dry unit weight with bentonite content 106
5.12 Test method samples 108
5.13 Variation of pH for different percentages of lime at different
bentonite contents 109
5.14 Variation of optimum lime content for different plasticity indices 109
5.15 Venco pug mill used in preparing SWEPS mixes 111
5.16 Typical SWEPS mix 111
6.1 Extruded SWEPS mix specimen 116
6.2 Compaction curves for SB16 at different EPS contents 117
6.3 Compaction curves for SB24 at different EPS contents 118
6.4 Compaction curves for SB32 at different EPS contents 118
6.5 Variation of maximum dry unit weight of soil with different
percentages of EPS at different bentonite contents 120
6.6 Variation in maximum dry unit weight with EPS content for
different soils 120
6.7 Compaction curves of decomposed granite mixed with HCCE 124
6.8 Soil – EPS volumes (a) as a composite (b) as individual components 125
6.9 Generalised volumes of EPS in SWEPS mix at different % of EPS by
Dry unit weight of soil 126
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Figure Title Page
6.10 The relation between the PI and the measured and predicted values of dry
unit weight 128
6.11 The relation between measured and predicted dry unit weights 128
7.1 Diagrammatic representation of static compaction of oedometer
Specimen 134
7.2 Variation of free swell with time at different EPS contents for SB16 136
7.3 Variation of free swell with time at different EPS contents for SB24 136
7.4 Variation of free swell with time at different EPS contents for SB32 137
7.5 Time-Free swell hyperbolic relationship for SB16 139
7.6 Free swell vs. time for SB16 at 0.0% EPS content 140
7.7 Free swell vs. time for SB16 at 0.3% EPS content 140
7.8 Free swell vs. time for SB16 at 0.6% EPS content 140
7.9 Free swell vs. time for SB16 at 0.9% EPS content 140
7.10 Free swell vs. time for SB24 at 0.0% EPS content 141
7.11 Free swell vs. time for SB24 at 0.3% EPS content 141
7.12 Free swell vs. time for SB24 at 0.6% EPS content 141
7.13 Free swell vs. time for SB24 at 0.9% EPS content 141
7.14 Free swell vs. time for SB32 at 0.0% EPS content 142
7.15 Free swell vs. time for SB32 at 0.3% EPS content 142
7.16 Free swell vs. time for SB32 at 0.6% EPS content 142
7.17 Free swell vs. time for SB32 at 0.9% EPS content 142
7.18 Differences in free swell values between experimental and hyperbolic
approximations (a) SB16, (b) SB24 and (c) SB32 143
7.19 Variation of maximum free swell with EPS content 144
7.20 Variation of maximum free swell with bentonite content 145
7.21 Variation of free swell with clay content for 0.0% EPS 146
7.22 Variation of free swell with clay content for 0.3% EPS 146
7.23 Variation of free swell with clay content for 0.6% EPS 146
7.24 Variation of free swell with clay content for 0.9% EPS 146
7.25 Relation between the PI and the measured and predicted values of
maximum free swell 147
7.26 The relation between measured and predicted maximum free swell 148
7.27 Variation of maximum swell pressure with EPS content 148
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Figure Title Page
7.28 Variation of maximum swell pressure with bentonite content 149
7.29 Relation between the PI and the measured and predicted values of
maximum free swell 150
7.30 The relation between measured and predicted maximum free swell 151
7.31 Reduction in swell pressure, free swell and dry unit weight for SB16 151
7.32 Reduction in swell pressure, free swell and dry unit weight for SB24 152
7.33 Reduction in swell pressure, free swell and dry unit weight for SB32 152
7.34 Variation of free swell with maximum dry unit weight for
different soils 153
7.35 Variation of swell pressure with maximum dry unit weight for
different soils 154
7.36 Variation of free swell and swell pressure with decrease in bentonite 154
7.37 Cyclic swelling test setup with CBR moulds 157
7.38 Variation of swell potential with increasing cycles for SB24 160
7.39 Variation of swell potential with increasing cycles for SB32 160
7.40 Variation in free swell with and without lime at various EPS contents 162
7.41 Variation of free swell with time with and without lime addition
for 0% EPS content 162
7.42 Variation of free swell with time with and without lime addition
for 0.3% EPS content 163
7.43 Variation of swell pressure with and without lime at various
EPS contents 163
7.44 Variation of axial shrinkage with bentonite content for four
different % of EPS 168
7.45 Variation of diametral shrinkage with bentonite content for
four different % of EPS 169
7.46 Variation of volumetric shrinkage with bentonite content for
four different % of EPS 169
7.47 Relation between the PI and the measured and predicted values
of volumetric shrinkage 173
7.48 The relation between measured and predicted volumetric shrinkage 174
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Figure Title Page
8.1 Direct shear apparatus used in the present study 178
8.2 Primary settlement of SWEPS mix with EPS at different normal
loads for (a) SB16, (b) SB24 and (c) SB32 181
8.3 Variation of primary settlement with bentonite content at
0.0% EPS content 182
8.4 Variation of primary settlement with bentonite content at
0.3% EPS content 182
8.5 Variation of primary settlement with bentonite content at
0.6% EPS content 182
8.6 Variation of primary settlement with bentonite content at
0.9% EPS content 182
8.7 Direct shear results for SB16 at 25 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 185
8.8 Direct shear results for SB16 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 185
8.9 Direct shear results for SB16 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 186
8.10 Direct shear results for SB24 at 25 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 186
8.11 Direct shear results for SB24 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 187
8.12 Direct shear results for SB24 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement. 187
8.13 Direct shear results for SB32 at 25 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 188
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Figure Title Page
8.14 Direct shear results for SB32 at 50 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 188
8.15 Direct shear results for SB32 at 100 kPa normal stress, (a) Shear stress
vs. shear displacement and (b) Vertical displacement vs. shear
displacement 189
8.16 Postulated shear failure mechanism of EPS beads 190
8.17 Variation of shear stress and shear displacement with 0.3% EPS for
different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa 191
8.18 Variation of shear stress and shear displacement with 0.6% EPS for
different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa 192
8.19 Variation of shear stress and shear displacement with 0.9% EPS for
different bentonite contents at (a) 25 kPa, (b) 50 kPa and (c) 100 kPa 193
8.20 Variation of shear stress with normal stress for SB16 194
8.21 Variation of shear stress with normal stress for SB24 195
8.22 Variation of shear stress with normal stress for SB32 195
8.23 Variation of cohesion with EPS 196
8.24 Variation of angle of internal friction with EPS 197
8.25 Triaxial testing equipment 199
8.26 A set of SWEPS test specimens after being tested 201
8.27 Stress - strain curves at different EPS contents for SB16 at confining
pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 203
8.28 Stress - strain curves at different EPS contents for SB24 at confining
pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 204
8.29 Stress - strain curves at different EPS contents for SB32 at confining
pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa 205
8.30 Stress-strain response of SB16 at different confining pressures for
EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and
(d) 0.9% EPS 206
8.31 Stress-strain response of SB24 at different confining pressures for
EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and
(d) 0.9% EPS 207
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Figure Title Page
8.32 Stress-strain response of SB32 at different confining pressures for
EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and
(d) 0.9% EPS 208
8.33 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB16 210
8.34 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB24 210
8.35 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB32 211
8.36 Composite modulus for SB16 at 25 kPa confining pressure 212
8.37 Composite modulus for SB16 at confining pressures of (a) 25 kPa
(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 213
8.38 Composite modulus for SB24 at confining pressures of (a) 25 kPa
(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 214
8.39 Composite modulus for SB32 at confining pressures of (a) 25 kPa
(b) 50 kPa , (c) 100 kPa and (d) 200 kPa 215
8.40 The relation between measured and predicted initial tangent Young’s
modulus 216
8.41 s-t plots for SB16 217
8.42 s-t plots for SB24 218
8.43 s-t plots for SB32 218
8.44 Variation of cohesion (c) and angle of internal friction (φ) for
different soils (a) SB16, (b) SB24 and (c) SB32 219
8.45 Typical failure modes of SWEPS mixes 220
8.46 Variation of cohesion with EPS for different soils 221
8.47 Variation of angle internal friction with EPS for different soils 221
8.48 The relation between measured and predicted cohesion 224
8.49 The relation between measured and predicted angle of internal friction 224
8.50 Failure envelopes of (a) SB16, (b) SB24 and (c) SB32 at various
EPS contents 226
8.51 Stress - strain curves at different EPS contents for SB24 with lime at
confining pressures of (a) 50 kPa, (b) 100 kPa and (c) 200 kPa 229
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Figure Title Page
8.52 Stress-strain response of SB24 with lime as stabiliser at different
confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS,
(c) 0.6% EPS and (d) 0.9% EPS 230
8.53 s-t plots for SB24 with lime 231
8.54 Variation of cohesion with and without lime for SB24 231
8.55 Variation of angle of internal friction with and without lime for SB24 232
9.1 Specimen preparation for suction measurement 240
9.2 Contact surfaces of the two halves and the EPS content at the interface 240
9.3 PVC ring separator above the soil specimen placed in an enclosed jar 240
9.4 Variation of total suction with EPS content for three soils 241
9.5 Variation of matric suction with EPS content for three soils 242
9.6 Variation of osmotic suction with EPS content for three soils 242
9.7 Variation of total suction with bentonite content at different
EPS contents 243
9.8 Variation of matric suction with bentonite content at different
EPS contents 244
9.9 Example of desiccation cracking in compacted clay in field 249
9.10 Desiccation specimens under observation 255
9.11 Extraction of surface cracking from specimens 256
9.12 (a) Photograph of the SWEPS mix and (b) Inverted image of the
photograph in black and white 257
9.13 Variation of CIF with EPS for 86 mm diameter specimens at varying
heights of (a) 20 mm and (b) 40 mm 258
9.14 Variation of CIF with EPS for 150 mm diameter specimens at varying
heights of (a) 20 mm, (b) 35 mm and (c) 70 mm 259
9.15 Variation of CIF with EPS for 150 mm diameter specimens at
varying heights for different bentonite contents of (a) SB16,
(b) SB24 and (c) SB32 261
9.16 Variation of CIF with EPS for 86 mm diameter specimens at
varying heights for different bentonite contents of (a) SB16,
(b) SB24 and (c) SB32 262
9.17 Variation of CIF with EPS for H/D of 0.47 at different bentonite
contents of (a) SB16, (b) SB24 and (c) SB32 264
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Figure Title Page
9.18 Variation of CIF with EPS for H/D of 0.23 at different bentonite
contents of (a) SB16, (b) SB24 and (c) SB32 265
9.19 Variation of CIF with EPS content for H/D of 0.47 and 0.23
for (a) SB16, (b) SB24 and (c) SB32 266
9.20 Variation of volumetric shrinkage with CIF 267
10.1 Variation of hydraulic conductivity with EPS 272
10.2 Typical log-time plot for the first increment of loading (a) 0.0% EPS,
(b) 0.3% EPS and (c) 0.6% EPS 275
10.3 Percent decrease in height with time at 200 kPa consolidation pressure 276
10.4 Variation of mv with EPS content 277
10.5 Variation of cv with vertical effective stress at different EPS contents 277
10.6 Variation of hydraulic conductivity with EPS content 278
10.7 Schematic representation of water balance computations by HELP
program 280
10.8 Variation of average annual percolation rate with EPS content 289
11.1 Compression and elastic rebound of pre-puff EPS beads upon loading
and unloading respectively 293
11.2 Flow chart for the mix design of SWEPS mixes 295
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LIST OF TABLES Table Title Page
2.1 General uses of EPS 11
2.2 Properties of EPS 12
2.3 The first documented use of EPS as a geofoam as lightweight fill in
different countries 15
2.4 Earlier applications of Soil-EPS mixes in Japan 18
2.5 Components for Soil-EPS mixes 22
2.6 Unit weight variations 23
2.7 EPS Products manufactured in Australia (state by state) in tonnes per
annum 31
3.1 Soil factors that influence swell-shrink movements 41
3.2 Environmental factors that influence swell-shrink movements of soils 41
3.3 Comparison between behaviour of non-expansive soils and expansive
soils 42
3.4 Different types of limes 50
3.5 Free vertical swelling strains and swell pressures 55
3.6 Average three-dimensional shrinkage strains of fibre treated soils 57
3.7 Swelling pressure of natural soil and soil with polymer additives 61
4.1 Properties of marine clay at different locations of the world 67
4.2 Effect of temperature on mass and volume of EPS cubes 71
4.3 Characteristics of the dredged soil 73
4.4 Wet unit weights of Soil-EPS mixes at different mix proportions 77
4.5 CBR Values of the Soil-EPS mixes 82
4.6 Unconfined compressive strength of Soil-EPS mixes 84
4.7 Swelling and shrinkage of the Soil-EPS mixes 90
5.1 Index properties of expansive soils from different locations around the
world 95
5.2 Properties of bentonite 98
5.3 Mineralogy of Miles bentonite 98
5.4 Bentonite content and mix properties 102
5.5 Variation of hygroscopic moisture content 103
xxvi
Table Title Page
5.6 Maximum dry unit weight and optimum moisture content of SB mixes 106
5.7 Optimum lime content for SB16 mix 108
5.8 Optimum lime content for SB24 mix 108
5.9 Optimum lime content for SB32 mix 108
5.10 Specific gravity of the soil with and without EPS beads 112
6.1 Effect of fibre reinforcement on MDD and OMC of cohesive soils 123
7.1 Shrinkage characteristics of SB mixes 167
7.2 Reduction in volumetric shrinkage strain with the addition of EPS 172
8.1 Shear displacement at peak stress at various normal stresses 183
8.2 Variation of peak shear stress with normal stress 184
8.3 Variables in triaxial testing 201
8.4 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB16 209
8.5 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB24 209
8.6 Deviator stress ( ) f31 σσ − and strain ( fε )at failure for SB32 209
8.7 Regression coefficients from failure envelopes 227
9.1 Calibration curves for Whatman No. 42 filter papers 238
9.2 Relationship between suction and shear stress for SB16 245
9.3 Relationship between suction and shear stress for SB24 245
9.4 Relationship between suction and shear stress for SB32 246
9.5 Variables in desiccation studies 254
10.1 Initial pressure and increments in pressure followed 274
10.2 Properties of soils used 285
10.3 Average annual totals for years 1 through 100 287
10.4 Variation of different parameters among different sites 288
10.5 Average annual totals for years 1 through 100 for Cairns 288
10.6 Average annual totals for years 1 through 100 for Perth 288
10.7 Average annual totals for years 1 through 100 for Alice Springs 289
xxvii
NOMENCLATURE
a Constant (slope of line in hyperbolic analysis of free swell)
b Constant ( intercept with y-axis in hyperbolic analysis of free swell)
c Cohesion (kPa)
Df Final diameter of specimen (m)
Di Initial diameter of specimen (m)
aε Axial shrinkage strain (%)
dε Diametral shrinkage strain (%)
fε Failure strain (%)\
es Free swell (%)
vε Volumetric shrinkage strain (%)
Eti Initial tangent Young’s modulus (kPa)
Gs Specific gravity of solids
Hf Final height of specimen (m)
Hi Initial height of specimen (m)
Ks Saturated hydraulic conductivity (m/year)
Kθ Unsaturated hydraulic conductivity (m/year)
qu Unconfined compressive strength (kPa)
t Time from the start of inundation (minutes)
Vcomp Volume of composite (expressed as 100%)
VEPS Volume of EPS (expressed as 100%)
Vf Final volume of specimen (m3)
Vi Initial volume of specimen (m3)
Vs Volume of soil (expressed as %)
Ws Dry mass of soil in the composite (kg)
1σ Peak major principal stress (kPa)
3σ Minor principal stress (kPa)
( )31 σσ − Deviator stress at failure (kPa)
dγ Dry unit weight of the composite (kN/m3)
φ Angle of internal friction (° )
xxviii
xxix
List of publications • Illuri, H. K and Nataatmadja, A. (2004), “Utilisation of dredged soil as
lightweight fill materials”, Proceedings of International Conference on Coastal Infrastructure Development- Challenges in the 21st Century, Hong Kong, 22-24 November 2004.
• Illuri, H. K. and Nataatmadja, A. (2004), “Engineering characteristics of a
soil-EPS composite”, Proceedings of 18th Australasian Conference on the Mechanics of Structures and Materials, Perth, 1-3 December, 2004, Vol. 2, pp.1013-1018, Rotterdam: Balkema.
• Illuri, H. K and Nataatmadja, A. (2007), “Shrink-swell and cracking of sand-
bentonite mixes with EPS inclusion”, 13th Pan-American Conference on Soil Mechanics and Geotechnical Engineering (Margarita 2007), Venezuela, 16-20 July, 2007.
• Illuri, H.K. and Nataatmadja, A. (2007), “Reduction of shrink-swell potential
with EPS inclusion”, 10th Australia and New Zealand Conference on Geomechanics, 21-24 October, 2007, Brisbane (Paper accepted)
Beinbrech, 1996; Siderius, 1998), construction materials for floating marine
structures and fenders in offshore oil platforms (Bagon and Frondistous-Yannas,
1976), sea beds and sea fences; as an energy absorbing material for buried
Chapter 2
17
military structures, (Cook, 1983; Perry et al., 1991) and tunnel covering
(Beinbrech, 1996).
2.4 Soil-EPS mixes as lightweight fill materials
The use of EPS beads in soil to produce lightweight fill materials is a new
concept. There are relatively few publications available on this topic. However, a
number of Japanese researchers, particularly those of the largest civil engineering
research institutes in Japan (Public Works Research Institute or PWRI in Tsukuba
and Port and Harbour Research Institute), have been working in this area since
1992. The following is a concise review of the techniques adopted by different
Japanese researchers.
In Japan, 45% of dredged soil, 21% of surplus soil from projects sites in the cities
and 8% of industrial waste are stored in the bulkheads every year (Okumura,
2000). As the availability of land for suitable disposal sites has become scarce, the
need to recycle the waste soil has arisen. In 1992, a research consortium
consisting of Port and Harbour Research Institute, Coastal Development Institute
of Technology and 23 research institutes affiliated with construction companies
was formed to develop a new fill material known as Super Geo Material (SGM)
using dredged and surplus soils (Tsuchida et al., 2001).
The lightweight fill material, obtained by mixing pre-puff EPS beads with waste
soils, was one of the research outcomes of the consortium. Where higher strength
was required, stabilising materials such as cement or fibre were used. The latter
was added to enhance the resistance to erosion. The manufactured material,
containing 60000 cubic metres of surplus construction soil was used in over 70
sites (Mori, 2003).
2.4.1 Features of Soil-EPS mixes
Miki (1996) explained that because of the inclusion of EPS beads, soil-EPS mix
is lighter than ordinary soil and thus can reduce the load applied to the ground.
Furthermore, it is nearly as flexible as ordinary soil and can cope with ground
subsidence. In addition, the strength can be adjusted to the requirements by the
Chapter 2
18
addition of a stabiliser appropriate to the soil type and compaction can be done as
with ordinary soil. This technique is suitable to all but gravelly soils (Mori, 2003).
2.4.2 Earlier applications
During this study, from the literature, it was observed that the new material (soil-
EPS mixes) had been used in a number of ports, harbours and other public
facilities in huge quantities (Table 2.4).
Table 2.4 Earlier applications of Soil – EPS mixes in Japan.
Project Quantity placed (m3)
Special features
Quay wall (10 m) in Port of Fushiki-Toyama1
900 First application in Japan
Quay wall (-7.5 m) in Port island, Port of Kobe1
21,610 First large-scale application in Japan. Use of dredged soil
Seawall and ground improvement in Tokyo international airport1
84,610 Use of sandy soil
Quay wall in Ishikari Bay New Port1 7,110 Use of mixture of soil on site and bentonite. Winter application in cold region
Ground improvement in Oi wharf, port of Tokyo1
11,200 Submerged application at –10m.
Quay wall (-7.5 m) in port of Yokohama1
70,000
Use of dredged organic soil Use of protein active agent
Hiroshima city, construction of high-tide river dike on soft ground2
1,500 To reduce settlement and to control lateral flow
Banking on a road in a landslide zone in Higashi-tagawagun2
1,800 To reduce loads and to provide a countermeasure against landslides
Banking on rear of embankment at Hachiohe city2
2,500 To reduce earth pressure and loads.
1 Okumura, 2000; 2 Miki, 1996
2.4.3 Construction processes
There are two construction processes for soil-EPS mixes which differ in the
machinery used and also in the mix compositions (Figures 2.4, 2.5 and 2.6).
Chapter 2
19
2.4.3.1 Construction process for dredged soil
Mud dredged from the seabed is collected in a floating barge. Large objects are
removed by a vibrating sieve installed on the agitation tank. Seawater is added
and regular measurements are performed to adjust the water content and density to
the desired level by �-ray density sensor and the prepared slurry is then supplied
to the mixing plant by sand pump. The pre-puff EPS beads and binder (Portland
cement) are subsequently mixed to control the density and strength of the
composite. If airfoam is used as lightweight material, a foaming machine is used
for mixing it with soil. Airfoam is generated from foaming agents prepared from
animal protein foaming material with a density of 0.031 t/m3 and compressed air
(Hayashi et al., 1998). The soil-EPS mix is placed in forms using a tremie pipe
(Tsuchida et al., 2001).
Figure 2.4 Construction process for port and harbour structures
(Satoh et al., 2001).
2.4.3.2 Construction process for surplus construction soil
Onsite mix method
In the onsite mixing process (Figure 2.5a), the pre-puff EPS beads and stabilising
agents (Portland cement or hydrated lime) are spread on the ground in uniform
thickness, and then, by using an excavator equipped with a special mixing blade
as shown Figure 2.5b, these additives are thoroughly mixed with the soil by
adding water in the required quantities. Finally, compaction is carried out by
levelling and rolling to the desired degree.
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Chapter 2
20
a. Mixing of EPS beads and stabiliser.
b. Mixing machine.
Figure 2.5 On-site mixing process (Miki, 1996).
Plant mix method
In the plant mix method (Figure 2.6), excess construction soil is transported to the
central mixing plant by trucks in which the pre-puff EPS beads and stabilising
agent suitable for the soil type are added along with water, and the resulting mix is
transported to the site where the levelling and compaction by rolling is carried out.
This method was reported to be more effective than on-site mixing process (Miki,
1996).
2.4.4 Mix proportion
As this technique is still in its infancy, there is no consistent mix proportion
adopted for all the cases. The mix proportions adopted by different researchers
and the corresponding wet densities obtained and the target compressive strength
are shown in Table 2.5.
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Chapter 2
21
a. Plant mix method.
b. Sealed batch type mixing plant.
Figure 2.6 Central mixing plant (Miki, 1996).
It is interesting to note that Satoh et al. (2001) and Tsuchida et al. (2001) added
water to the dredged bay mud (initial moisture content = 84%) to reach a moisture
level of 2.5 times the liquid limit (i.e. slurry form) to reduce its density. Miki
(1996) used the same technique but did not comment on the initial water content
of the soil and the rationale behind the subsequent addition of the water. In all of
the above mixes, the aim was to reach the target unconfined compressive strength
(UCS) after 28 days, after mixing. However, it is to be noted that the UCS is
obviously influenced by the moulding moisture content of the soil.
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Chapter 2
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Table 2.5 Components for Soil-EPS mixes.
Soil (kg)
EPS Beads
(l)
Stabiliser (kg)
Water (l)
Wet Density (t/m3)
UCS (kPa)
Ariake clay 1 (dry)
367 to 375
215 to 224
80 to 100
(Cement)
625 to 638
1.2 200
Tokyo bay mud2 (dry)
789 161 100 (Cement)
261 1.2 559
Tokyo bay mud2 (under water)
714 206 200 (Cement)
236 1.2 1601
Sandy soil3 (� = 1.8 t/m3)
900 850 40 (Cement)
50 1.0 98
Sandy soil3 (� = 1.8 t/m3)
1120 630 30 (Cement)
40 1.2 98
Cohesive soil3 (� = 1.6 t/m3)
950 650 40 (Lime)
0 1.0 98
Cohesive soil3 (� = 1.6 t/m3)
1140 470 50 (Lime)
0 1.2 98
Cohesive soil with high water content3 (� = 1.6 t/m3)
940 530 50 (Lime)
0 1.0 98
Cohesive soil with high water content3 (� = 1.6 t/m3)
1140 330 50 (Lime)
0 1.2 98
1Satoh et al., 2001; 2Tsuchida et al., 2001; 3Miki, 1996
2.4.5 Properties
2.4.5.1 Wet unit weight: The wet unit weight of the soil-EPS mix can be set in
the range of 6 kN/m3 to 20 kN/m3 depending upon the mix proportion of the soil,
pre-puff EPS beads and the hardening agent such as lime or cement as shown in
Figure 2.7 (Miki, 1996).
For under seawater placement at Kumamoto port, Satoh et al. (2001) poured soil
mixed with EPS beads inside concrete caissons (Figure 2.8). and studied two
cases. The soil-EPS mix was placed at 4.7 m deep in two separate chambers (Case
3 and Case 5) by varying the cement content between 80 kg/m3 and 100 kg/m3.
The variation in unit weight after mixing is presented in Table 2.6.
Chapter 2
23
Clays
Sandy soil
6
8
10
12
14
16
18
20
0 0.5 1 1.5 2 2.5 3
Mixture ratio of expanded beads to soil, %
Wet
un
it w
eig
ht,
kN
/m3
Figure 2.7 Relationship between wet unit weight and mixture ratio of EPS beads
(after Miki, 1996).
Figure 2.8 Sections of caissons and testing cases (Satoh et al., 2001).
Table 2.6 Unit weight variations (Satoh et al., 2001).
The dredged clay was diluted to a water content of about 170% (2.6 times liquid
limit) so as to reduce the unit weight of the dredged clay from 16.2 kN/m3 to 13.0
kN/m3 (slurry). Another layer of foam treated soil of 5.2 m was placed above the
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Chapter 2
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soil-EPS mix. The variation of the wet unit weight immediately after mixing for
each case is shown in Figure 2.9. In the same figure, the measured range of the
wet unit weight of the lightweight treated soil just after being transported to the
site is also shown. It can be seen that in all the cases, the wet unit weights after
transportation were larger than the wet unit weight immediately after mixing.
Satoh at al. (2001) attributed this to the pressure in the transportation pipe and the
separation and loss of EPS beads during placing. The maximum compression in
the transportation pipe was 100 ~ 150 kPa, which might have caused the
irrecoverable compression of EPS beads. Furthermore, it was also observed that
during the underwater placement some of the EPS beads were separated and
drifted to the water surface, this volume was about 2% to 3% of the total beads
mixed. The change in the wet unit weight after one year is shown in the Figure
2.10. It is seen that the unit weight marginally increased after one year for the
same composite.
Figure 2.9 Wet unit weight of soil-EPS mix immediately after placing
(Satoh et al., 2001). In another study, Minegashi et al. (2002) studied the relationship between the
percentage of EPS beads and the wet unit weight of the soil-EPS mix. The trend is
shown in Figure 2.11. Note that in order to achieve sufficient homogeneity; the
moisture content of the composite was kept at 120%, which was 25.3% above the
optimum moisture content.
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Chapter 2
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By comparing Figures 2.7 and 2.11, it can be concluded that the unit weight of the
composite is generally influenced by the bead content due to the lightweight of
EPS beads. These studies were performed at moisture content well above their
optimum moisture content. However, what limits the addition of EPS at around
optimum moisture content is not known. This factors needs to be assessed.
Figure 2.10 Change in wet unit weight after one year (after Satoh et al., 2001).
Moisture Content = 120%
0
1
2
3
4
8 9 10 11 12 13 14 15Apparent density, kN/m3
Per
cent
age
of E
PS
bea
ds, %
Figure 2.11 Change in apparent unit weight with mixing rate of beads
(after Minegashi, 2002).
Chapter 2
26
2.4.5.2 Unconfined compressive strength
Figure 2.12 shows the relationship between wet density and unconfined
compressive strength of a soil with and without EPS beads (after Miki, 1996).
Figure 2.12 Relationship between the wet density and UCS (after Miki, 1996).
As can be observed from the figure, the strength gain in EPS beads mixed soil
may only be achieved by the addition of stabiliser contents. Without stabiliser the
UCS varies between 50 to 200 kPa, whereas the UCS can be increased to about
1000 kPa with increase in stabiliser content. It should be noted that the addition of
stabiliser and the corresponding strength gain is influenced by the initial water
content of the soil (Bell, 1996). It is not known whether the strength gain in the
Figure 2.12 was obtained at the same moisture content.
The unconfined compressive strength of a dredged soil mixed with EPS beads and
cast underwater is shown in Figure 2.13 (Satoh et al., 2001). The specimens were
obtained by core cutting. It was found that the unconfined compressive strength
was much larger than the target value, i.e. 200 kPa. In addition, the UCS is almost
independent of the water depth and the type of the lightweight materials, but was
strongly controlled by the cement content.
Chapter 2
27
Figure 2.13 Variation of UCS with depth (Satoh et al., 2001).
The relationship between the modulus of deformation or secant modulus, E50 (in
kPa), and unconfined compressive strength, qu (in kPa), was expressed by Satoh et
al. (2001) as E50 = (189 to 359)qu. However, this is significantly larger than the
values reported by Tsuchida et al. (1996), E50 = (100 to 200)qu.
2.4.5.3 Stress-strain behaviour
Figure 2.14 shows the stress-strain curve from an unconsolidated undrained (UU)
test for a dredged soil at moisture contents of 2.5 times the liquid limit at different
confining pressures (Tsuchida et al., 1996). It can be seen from Figures 2.15 and
2.16 that the stress-strain behaviour of soil-EPS mix is influenced by the soil type
and cement content (Pradhan et al., 1993; Minegashi et al., 2002). As can be seen
from the Figure 2.15 for soft clay, no peak strength were observed where as in
Figure 2.16 for sand, different peak strengths were observed for different
confining pressures from drained triaxial compression tests. In the former, the
moisture content of the mix was 25% above the optimum moisture content
(OMC), while the latter had a moisture content of 10% above the OMC.
Furthermore, Pradhan et al. (1993) observed that the increase in cement content
increased the compressive strength. This was predominant at higher densities, i.e.
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Chapter 2
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with less EPS bead content. A similar trend was observed with the change in
stiffness, at higher cement contents the material became stiffer and brittle. Cement
is thus an important ingredient for the strength gain in the composite and
facilitates bonding of the beads and soils.
Figure 2.14 Stress-strain curves for a dredged soil mixed with EPS beads at a
moisture content of 2.5 times liquid limit (Tsuchida et al., 1996).
Furthermore, Minegashi et al. (2002) observed that a softening of stress-strain
relation of the composite under repetitive loadings continued with the increase in
the dynamic stress ratio, and decreased with the increase in the confining pressure.
In addition, it was found that the cement additive contributed to the increase in
cohesion but not to the angle of shear resistance, and the beads may not contribute
to the frictional resistance.
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Chapter 2
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Figure 2.15 Stress-strain curves for the Ariake bay mud at liquid limit
(Minegashi et al., 2002).
Figure 2.16 Stress- strain curves for the sand mixed with EPS beads with moisture
content 10% above the optimum moisture content (after Pradhan et al., 1993).
Oh et al. (2002) mixed recycled EPS beads with weathered granite soil and
studied the bearing capacity of the layers. The first layer was a soft soil and it was
overlain with granite soil with EPS inclusion. It was observed that the ultimate
bearing capacity increased with the height of the upper lightweight materials. In
addition, the ultimate bearing capacity decreased with the increase in EPS content.
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Chapter 2
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Yoonz et al. (2004) investigated the mechanical characteristics of a dredged soil
mixed with EPS beads and cement. The moisture content of dredged soil was
135% which was 3 times its liquid limit. Two percent EPS beads were added to
the mix with 35 times the foaming effect. The cement ratio was 2%. The dredged
soil had a liquid limit of 45%, plasticity index of 25% and passing 200 number
sieve was 95%. The soil was classified as clay with low plasticity (CL). They
observed that with initial water contents and EPS ratios ranging from 165-175%
and 3-4%, respectively, the mixes could achieve a compressive strength exceeding
200 kPa. Furthermore, the ultimate triaxial compressive strength of the soil did
not increase when the cement ratio was above 2%. However, they observed that if
the curing pressure of above 200 kPa was applied, the ultimate compressive
strength could increase further.
2.5 EPS applications in Australia
2.5.1 Lightweight fill
In Australia, VicRoads has been using lightweight expanded polystyrene foam
blocks for general road works since 1985, on projects such as bridge approach
embankments and lightweight embankments over soft soils. The organisation has
also developed a new technique, which has become known as the “EPS
embankments repair” (Brown, 2000). They found that the use of geofoam to
minimise the sub-soil stress was cost effective and had allowed construction
programs to proceed without delays of the kind normally associated with ground
treatment and pre-consolidation.
2.5.2 Packaging products
While EPS is a good packaging medium for transporting fragile and expensive
items, the majority of the packaging materials manufactured in Australia are used
for transporting fruit, vegetables and seafood (Table 2.7). The use of EPS for this
purpose is extensive in both the domestic and export markets (Fisher, 2000).
In an Australia-wide plastics recycling survey for the year 2004 conducted by
Plastics and Chemicals Industries Association (PACIA, 2005), it was observed
that nearly 36,000 tonnes of expanded polystyrene were consumed in Australia in
Chapter 2
31
2004. Of this, domestic reprocessing was 1600 tonnes and export for reprocessing
was 907 tonnes, which means a total recycling rate of 7.1%.
There are 17 reprocessing sites for EPS products in Australia. Most non-
packaging applications such as building and panel applications as shown earlier in
Table 2.1 would have longer application and take a longer time to reach for
recycling. The utilisation of EPS in single-use or short term packaging
applications is 35% and for long-term durable applications it is 65%. The recycled
EPS is used as waffle pods in building and wall panels.
About 39% of the produce boxes are collected by the EPS recycling group at the
collection centres, located at different mainland cities in Australia for possible
recycling (PACIA, 2005). At these collection centres, the waste EPS is placed in a
large granulation machine where it is broken up and fed into a large bag above the
compaction machine. These granulates are then compressed into pallets of
approximately 120 mm wide and forced out of the machine into suitable lengths.
These ingots are used as a general purpose plastic for manufacturing of toys,
cassette casings, coat hangers, synthetic timber etc.
Table 2.7 EPS Products manufactured in Australia (state by state) in tonnes per annum (PACIA, 2002a).
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Chapter 2
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2.6 Management of waste EPS
As described in the previous sections, EPS is undoubtedly a very versatile
material that has found useful applications in general public as well as in civil
engineering and geotechnical engineering in particular. With the ever increasing
demand for consumer goods, the use of EPS as a packaging material is growing
rapidly owing to its lightweight and exceptional insulation qualities. This
significant increase in the use of EPS has led to a growing public concern over its
impact on the environment and the dwindling landfill space (Lye et al., 2002;
Shin, 2005). This is because EPS being non-biodegradable, light in weight and
having a low mass-to-volume ratio, takes up a significant amount of space in
already overcrowded landfills.
Once its use as packaging materials ends, EPS is sent to the disposal or recycling
centres. Unlike other waste materials, whose disposal raises concerns about
possible contamination of soil or ground water because of leachability, concerns
about EPS disposal relate to the volume occupied and its non-biodegradability.
Because EPS can not be decomposed in nature, waste EPS has caused serious
environmental problems, including ocean pollution. According to one estimate
(Ikada, 1990), in 1988, 25% of total floating debris in the North Pacific Ocean
was waste EPS. In Europe, the originating manufacturer is now responsible for
the collection, recycling or disposal of waste EPS products (PPW Directive,
2005).
According to Schiers (1998), the cost of land-filling waste EPS can be between
$500 and $2500 per tonne. Added to this are the high transportation costs
associated with shipping low bulk density waste EPS. Furthermore, any attempt to
recycle EPS products would involve various technological challenges mainly
because of the low mass-to-volume ratio of the material which is a barrier to the
collection for recycling (PACIA, 2005). In light of the high cost of disposal and
growing consumer awareness of land filling and impositions from the
governments, the manufacturers have been forced to devise alternative reuse and
recycling strategies for EPS disposal.
Chapter 2
33
2.6.1 EPS recycling methods
Various techniques are available for recycling EPS waste products:
(i) Material Recycling: In this method, EPS products sorted and segregated from
the solid waste stream are reduced in volume by densification or compaction of
the foam by means of hot air, IR lamps, friction, heated rotary drum etc. such that
polystyrene can be recovered as an ingot or pellet, or reused into raw material,
daily products, construction materials etc. (Noguchi et al., 1998; Scheirs, 1998;
PACIA, 2005). Densification of EPS involves the complete or partial collapse of
the cell structure because of the expulsion of air from cell. A critical issue in the
densification of EPS is the degradation of the polymer and the associated property
deterioration (Scheirs, 1998).
(ii) Chemical Recycling: In chemical recycling methods, the main idea is to
recover the styrene monomer which can be reused as a chemical resource. This is
achieved by dissolving the EPS in d-limonene – a biodegradable solvent derived
from the rinds of citrus fruits (Noguchi et al., 1998).
(iii) Thermal Recycling: Thermal recycling of EPS waste products involves their
incineration to recover the energy from its burning. However, since EPS has a
poor energy density per volume because it contains so much air, the transportation
of the required bulk volume becomes uneconomical.
2.6.2 Constraints and challenges in EPS recycling
The recycling processes described above can be labour intensive and expensive.
Furthermore, the processes can ruin the properties of EPS and demand high
energy requirements for conversion (Fisher, 2000; Shin and Chase, 2005). Hence,
in spite of the recycling techniques mentioned above, EPS usually ends up in
landfills or is incinerated, due to the following reasons (Reneker and Chun, 1996;
Lye et al., 2002; Shin, 2005).
• Places like wholesale markets, supermarkets, department stores, restaurants,
electrical appliance stores and factories generate large volumes of EPS
packaging products in their daily operations. However, in most cases, efficient
Chapter 2
34
collection of the waste EPS products from consumers, either as voluntary
drop-off or as buy-back, for recycling is minimal or sometimes absent. In
addition, unlike aluminium cans, PET bottles etc., household EPS packaging
represents a small portion of the residential solid waste stream, hence
community based recycling programs generally do not add EPS to their list of
material for collection since such quantities hardly justify the associated
transportation costs and subsequent mechanical recycling expenses (AFPR,
2001).
• Furthermore, during loading, transportation, and unloading of goods, the EPS
packaging might be damaged, making its re-use as packaging not a good
option. Additionally, to transport it back to the manufacturing unit is not cost
effective because of the low mass-to-volume ratio and the manufacturing units
are located in different states/countries.
• In addition, the cost difference between using recycled and pre-puff EPS
materials is not significant. The cost to process the recycled materials far
outweighs any returns from the sale of the materials (Fisher, 2000). And since
there is no uniform rate applied to the disposal of wastes at municipal
landfills, it is difficult to set prices at industry collection centres.
• Recycled EPS products tend to have more inferior properties than their pre-
puff (virgin) counterparts, thereby reducing their demand (Lye et al., 2002).
This is because recycling process requires post-consumer plastic materials to
be melted and remoulded through an extrusion heat cycle, which affects the
chemical and physical structure of the EPS. For example, the expansion
characteristics of recycled EPS differ from that of the natural bead of virgin
foam (Hornberger, et al., 2000). Furthermore, the bead fusion between the
new and recycled materials is not good because the recycled EPS beads
usually contain minimum or no pentane gas in them, which hinders the
effectiveness in expansion and subsequent fusion with the pre-puff in the
mould. It primarily serves as a “dead” filler material only. The damage due to
grinding or heating and the inability to expand results in void spaces in
manufactured product, which may weaken the product. To improve the
Chapter 2
35
density, recycled EPS beads need to undergo a specific treatment through a
densifier, pretreating them again with pentene gas, which would result in an
increase in the production cost for the recycled EPS beads.
• Finally, the application areas where EPS is employed are dictated by the
nature of the process. Presently, steam-injection, extrusion or palletisations are
the key processes that make use of the recycled materials for mass
manufacture of EPS products. Such processes are not suitable and cost-
effective in the handling of one-off or small batch prototyping and moulding
(Lye et al., 2002).
In reusing post-consumer recycled material for the manufacture of EPS geofoam,
Horvath (1995) mentioned the technical difficulty of commingling of EPS made
from regular and modified (flame-retardant) expandable polystyrene as they are
visually indistinguishable. This would affect the flammability of the final product
of EPS used in cushion packaging. Furthermore, Horvath (1995) states that
because of the problems associated with both mechanical properties and
flammability, there has been no regular large-scale production of EPS block
geofoam that uses a significant percentage of recycled EPS at least in USA.
Manufacturers of EPS products expressed concerns for recycling of the waste EPS
products back into the production cycle on the following technical grounds
(AFPR, 2001)
1. It is difficult for the consumer to distinguish EPS foam from polyethylene
foam, which is often a contaminant in the EPS brought to the reprocessing
centre because the properties of both materials significantly different.
2. It is difficult to remove dirt and grease from EPS foam. Consequently,
much of the waste EPS foam (foam plates and foam packaging) is not
currently processed.
3. Even though EPS is moisture resistant, foamed material absorbs some
water (1% to 5%) when washed or stored in open containers. This
increases the density of the EPS material making it more difficult to
weigh, sort and handle.
Chapter 2
36
4. Some EPS materials contain additives or co-polymers such as flame-
retardants, lubricants, antioxidants etc. When these materials are mixed
with foam packaging and other waste that do not contain flame-retardants,
the result is a material that has different flow behaviour and property.
Flame retardant material is therefore considered to be a contaminant in the
current EPS recycling processes as it can ruin the entire batch of material.
5. Because the beads are made through an extrusion/palletisation process,
they are not perfectly spherical as are the beads made from suspension
polymerisation process. As a consequence, the final expanded product
could have a higher level of void spaces between the beads which weakens
the product.
All of the above necessitate a need to try for other alternatives for the recycling of
EPS products in other engineering fields to enhance their value as suitable
recycled material. Utilisation in civil engineering applications could be a good
option particularly if a large amount of EPS can be accommodated in an
environmentally friendly or cost effective manner. Use of waste materials
including tyre chips, fibres from PET bottles etc., for various geotechnical
applications is increasing around the world (Eighmy and Magee, 2001; Sherwood,
2001; Inyang, 2003). Hence, the use of waste EPS for the modification of
problematic soils, to enhance its value for reuse or recycle can also be
investigated.
2.7 Summary
So far, Japanese researchers have only considered the use of pre-puff EPS beads
as a component of lightweight fill materials. While their work has been motivated
by the need to manage waste soils, their published results have encouraged a
separate study on the use of crushed waste EPS in earthworks. EPS recycling is
feasible, and studies are progressing, but effective recycling is hampered by the
low bulk density, high volume and fragmented nature of the product. While waste
EPS granules have been used in with horticultural soils to improve a number of
soil characteristics like improving its drainage, lightening heavy soils and
improving water uptake capacity of soils, there are very limited applications
reported in geotechnical engineering.
Chapter 2
37
This thesis is the first of its kind in investigating the possibility of reusing waste
EPS as a swell-shrink modifier in clays and in doing so, may open up the
possibility of using soil-EPS mixes behind retaining walls, under foundations and
as a landfill cover material. The reuse of waste expanded polystyrene in
geotechnical engineering will support the principle of sustainability in
construction.
The mixing of EPS beads with soils would not require specialised equipment. As
an engineered material, soil-EPS mixes can be designed to meet specific
requirements for each application depending on the mix design. EPS beads can
provide cushioning and also take care of loads due to their compressible nature as
is evidenced in packaging; these characteristics may benefit the application of
waste EPS as a soil modifier in expansive soils and as a lightweight cover material
for landfill. The earlier Japanese studies were conducted at higher moisture
contents and utilised chemical stabilisers for strength enhancement. However, it
may be possible to prepare soil-EPS mixes at lower moisture content values such
that the performance can be optimised. With these objectives in mind, Chapter 3
presents a short review of expansive soils.
Chapter 2
38
39
CHAPTER 3 - EXPANSIVE SOILS AND THEIR TREATMENTS ___________________________________________________________
As mentioned in Chapter 1, the inclusion of EPS to expansive soils may offer an
alternative method to chemical stabilisation techniques and other methods for
reducing swell-shrink potential. By substituting part of the expansive soil with
EPS, the soil performance may be improved such that total soil replacement can
be avoided. Intuitively, the performance of the soil-EPS mix will depend on the
nature of the expansive soil.
In this chapter, a background review on expansive soils, considered problematic
around the world including in Australia, is presented. The various factors that
influence the behaviour of expansive soils and their distribution in Australia are
presented. This is followed by their characteristic features like swelling,
shrinkage, desiccation, suction and available treatment options are described.
3.1 Expansive soils
Expansive soils are clays or very fine silts that have a tendency for volume
changes, to swell and soften or shrink and dry-crack, depending on the increase or
decrease in moisture content respectively. These swell-shrink movements in
expansive soils have historically caused frequent problems because of the
unpredicted upward movements of the structures or cracks in the pavements
resting on them. In addition, they also affect the serviceability performance of
lightweight structures supported on shallow and relatively flexible footing
systems and pavements. For example, “doming” (centre heave) and “dishing”
(edge heave) curvatures in foundations would result because of soil movements.
Doming can be due to the long term progressive swelling beneath the centre of
slab and dishing can be due to the cyclic heave beneath perimeter of the
foundation (Masia et al., 2004; Day, 2006).
Expansive soils are a worldwide problem spreading in the semi-arid regions of the
tropical and temperate climate zones across five continents (Chen, 1988). The
primary problem that arises with regard to expansive soils is that deformations are
significantly greater than elastic deformations and they cannot be predicted by
Chapter 3
40
classical elastic or plastic theory. Movement is usually in an uneven pattern and of
such a magnitude that it causes extensive damage to the structures and pavements
founded on them (Nelson and Miller, 1992).
In the U.S.A., it was estimated that expansive soils create more damage to
structures, worth billions of dollars, particularly to light buildings and pavements,
than any other natural hazard, including earthquakes and floods (Jones and Jones,
1987; Nelson and Miller, 1992). Several countries in the world, including
Australia, the United States of America, Israel, India and South Africa have
reported infrastructure damage problems caused by the movement of expansive
soils (Chen, 1988).
3.2 Factors influencing mechanisms in expansive soils
There are many factors that govern the expansion behaviour of soil. The
mechanism of shrinkage and swelling in expansive soils is rather complex and is
influenced by several physical and chemical properties such as clay content, type
of clay mineral, crystal lattice structure, cation exchange capacity, ability of water
absorption and environmental factors like moisture conditions of the site,
magnitude of surcharge load, to name a few. Nelson and Miller (1992)
summarised various factors into three groups, viz., soil characteristics,
environmental factors and state of stresses.
Soil characteristics influence the basic nature of the internal force field, which
depend on the negative surface charges of clay particles and the electrochemistry
related reaction with water. In addition, the swelling capacity of an entire soil
mass depends on the amount and type of clay minerals in the soil, the arrangement
and specific surface area of the clay particles. Furthermore, on a macro scale, the
dry unit weight and physical arrangement of particles will also affect the swell
potential (Nelson and Miller, 1992). Environmental factors influence the change
of the soil-water system that affects the internal stress equilibrium, the state of
stress influences the changes in particle spacing, which in turn influences internal
stress equilibrium (Punthutaecha, 2002). Tables 3.1 and 3.2 present the influence
of various soil and environmental factors (after Nelson and Miller, 1992) and
Table 3.3 summarises the behaviour between non-expansive and expansive soils
(Katti, 1987).
Chapter 3
41
Table 3.1 Soil factors that influence swell-shrink potential (adapted from Nelson and Miller, 1992). Factor Description
Clay mineralogy Montmorillonites, vermiculites and some mixed layer minerals exhibit considerable soil volume changes
Soil water chemistry
Increase in cation concentration and increase in cation valence hold back the swelling
Soil suction Soil suction is an independent effective stress variable, represented by the negative pore pressure in unsaturated soils. Soil suction is associated with saturation, gravity, pore size and shape, surface tension and electrical and chemical characteristics of the soil particles and water
Plasticity Soils exhibit plastic behaviour over wide ranges of moisture content and that have high liquid limits exhibit greater potential for swelling and shrinkage
Soil structure and fabric
Flocculated clays tend to be more expansive than dispersed clays. Cemented particles reduce swell. Fabric and structure are altered by compaction
Dry unit weight Higher unit weights usually indicate closer particle spacing, which may mean greater repulsive forces between particles and larger swelling potential
Table 3.2 Environmental factors that influence swell-shrink potential of soils (adapted from Nelson and Miller, 1992). Factor Description
Moisture content
Changes in moisture in the active zone near the upper part of the soil profile primarily define heave. It is in those layers that the widest variation in moisture and volume change will occur
Climate Amount and variation of precipitation and evapotranspiration greatly influence the moisture availability and depth of seasonal moisture fluctuation. Greatest seasonal heave occurs in semiarid climates that have pronounced short wet periods
Ground water Shallow water tables provided a source of moisture and fluctuation water tables contribute to moisture
Drainage and man made water sources
Surface drainage features provide sources of water at the surface; leaky plumbing can give the soil access to water at greater depth
Vegetation Trees, shrubs and grasses deplete moisture from the soil through transpiration, and can cause the soil to be differently wetted in areas of varying vegetation
Permeability Soils with higher permeability allow faster migration of water and promote faster rates of swell
Temperature Increasing temperature cause moisture to diffuse to cooler areas beneath pavements and buildings
Stress history An over consolidated soil is more expansive than the same soil at the same void ration, but normally consolidated
Loading Magnitude of surcharge load determines the amount of volume change that will occur for a given moisture content and density. An externally applied load acts to balance inter-particle repulsive forces and reduces swell
Chapter 3
42
Table 3.3 Comparison between behaviour of non-expansive soils and expansive soils (adapted from Katti, 1987).
Behaviour Condition Conventional
clayey soil (Non – expansive )
Expansive soil
During saturation from dry to saturated conditions, under a (i) nominal load (ii) as the load increases
Settles Settles more
Heave upwards. Heave goes on reducing and reaches zero at some load and then starts settling
Moisture content with depth say up to around 10 m under free water standing on the top and under fully saturated conditions
Remains almost constant throughout the depth
Near liquid limit at the surface and goes on decreasing rapidly up to around 1 to 1.5 m and then remains constant
Density with depth under saturated condition say up to 10 m depth
Remains almost constant throughout the depth
Very low near the surface and goes on increasing rapidly up to 1 to 1.5 m depth and then remains constant
Undrained cohesion ‘cu’ with depth – vane shear
Remains almost constant
Negligible near the surface and goes on increasing rapidly up to 1 to 1.5 m and then remains almost constant
Density with depth under summer condition
Somewhat more closer to surface and then remains almost constant
High nearer the surface and goes on decreasing rapidly up to 1 to 1.5 m and then almost remains constant irrespective of moisture changes
Lateral pressure with depth for saturated case
Behaves according to Terzaghi’s concept. No lateral pressure up to 2c/�
Negligible near the surface and goes on increasing rapidly with depth up to 1 to 1.5 m and then remains almost constant. Lateral pressure value at 1 to 1.5 m is equal to swelling pressure. Value of swelling pressure at no volume change condition can be as high as 3 to 5 kg/cm2 depending upon soil
K0 at saturated condition Less than 1 Up to 1 to 1.5 m. the value is 15 to 20 and with increase in depth is also greater than 1. 2 to 3 is common
K0 value at saturated condition Less than 1 Up to 1 to 1.5 m. for tolerable wall movement almost 15, then beyond >1, 2 to 3 is common
Chapter 3
43
3.3 Distribution of expansive soils in Australia
Expansive soils are widespread throughout Australia. The distribution of the
major areas of expansive soils in Australia is shown in Figure 3.1 (Richards,
1990; Look, 2005). The expansive soils include some 75 million hectares of “grey
and brown soils of heavy structure” and 33 million hectares of “black earths”
(Rankin and Fairweather, 1978).
The grey and brown soils are typified by the soils of the “rolling downs”, which
extend through mid-west Queensland from Roma to the Gulf of Carpentaria. The
group is broad, accommodating wide ranges in some properties, particularly
surface structure, reaction profiles and Gilgai. In South Australia, the clay
fractions are illite dominated with 20-30% kaolin; in the east and north they are
montmorillonite-kaolin mixtures with some illite (Wallace, 1988).
Figure 3.1 Distribution of expansive soils in Australia (Richards, 1990).
The “black earths”, overwhelmingly montmorillonite-dominant, include the black
soil of the Darling Downs. The majority of these expansive soils are located
within the 250 to 1000 mm isohyets, extending from North-Western Australia,
thorough the eastern states and into the South-East of Australia (Rankin and
Fairweather, 1978). It has been found that the most troublesome soils in terms of
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Chapter 3
44
volume changes are the black earths, red-brown earths, and the grey and brown
soils of heavy texture. According to Hubble (1972) these soils are found in parts
of Adelaide, Victoria, New South Wales and Queensland.
3.4 Characteristics of expansive soils
Expansive soils are mainly characterised by the swell-shrink potential in relation
to total suction variations through moisture changes, desiccation cracking
behaviour and corresponding strength changes. The expansive soils near ground
surface are generally unsaturated due to desiccation and are commonly self-
mulching, that is, they form a relatively thin surface layer of loose dry granular
material following repeated light wetting and drying (Hubble, 1972).
In the dry state, expansive soils are hard and dense and possess high shear
strength. They are characterised when dry by the existence of the large cracks
(Figure 3.2), which may be up to a maximum of 50 mm in width at the surface,
often tapering and extending down to depths of 1 to 2 m or more in deep
expansive soils and they may be continuously interconnected over several metres
or more in plan dimension. Generally, the spacing and width of cracks are related
(Hubble, 1972; Wallace, 1988).
Figure 3.2 Shrinkage and cracking of expansive soils (Hey, 1999).
During the periods of rainfall, the presence of these open cracks and other planar
voids bypasses the infiltrating water directly to the bottom of the cracks. This
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Chapter 3
45
could allow deep wetting of the expansive soil from heavy rain far more rapidly
than could result from moisture infiltration through the uncracked soil. The entry
of water depends on the previous extraction process. In addition to increasing the
hydrostatic forces, the water is slowly absorbed by the expansive clay. The
gradual wetting of dry soil from the crack bottom causes uplift forces which
further generate heaving of the ground surface surrounding the crack in restrained
environments (Kodikara et al., 1999). Furthermore, high lateral stresses can build
up that result the soil to fail in shear. The more cracks in the clay, the greater the
pathways for water to penetrate the soil, and the quicker the rate of swelling (Day,
2006).
The expansive soils become very sticky upon wetting (Figure 3.3). Furthermore,
they suffer a rapid loss of shear strength associated with expansion and loss of
unit weight as moisture content increase and subsequent release of negative pore
water pressures (Petry and Armstrong, 1989). This is due to the volume changes
occurring because of wetting and drying. These mechanisms result in a
simultaneous increase of the sliding (driving) forces and decrease of the resisting
(shear strength) forces.
Figure 3.3 Wetting and loss of strength in expansive soil (Hey, 1999).
An unsaturated expansive soil will undergo volume changes when the net normal
stress or the matrix suction changes in magnitude (Nishimura, 2001). Bronswijk
and Evers-Verman (1990) observed volumetric expansion by as high as 49% upon
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Chapter 3
46
wetting in natural heavy clays (cited by Kodikara et al., 1999). Furthermore, if
this expansion is prevented, swelling pressure greater than 1 MPa may occur
(Bradford, 1978). The magnitude of swell occurring is directly related to the dry
unit weight and inversely related to the moisture content. In addition, the higher
the volume changes occurring in soils, the greater the potential for cracking in that
soil (Kodikara et al., 1999).
An uncracked sample of a moist clay is virtually impermeable, and infiltration and
drainage under these conditions is very slow. The presence and spacing of open
cracks therefore play an important part in wetting up the soil profile following a
dry period. Large quantities of water from heavy rain, loose surface material, and
other debris are able to enter the cracks before they are closed by soil expansion
and results in damaging differential movement. Furthermore, the combination of
shrinkage cracks and high suction pressure resulting from low moisture content,
allows water to be quickly sucked into the clay, resulting in a higher magnitude of
swell (Day, 2006). As the soil dries, the total suction increases, with subsequent
shrinkage of the soil. Likewise, if the soil is wetted, the total suction decrease, and
the soil expands. In addition, remoulded clay can have higher swell potential than
that of the same clay undisturbed because of the rupture of interparticle bonds that
inhibit the swelling and from the differences in fabric (Mitchell and Saga, 2005).
3.5 Effects of expansive soil on different structures
3.5.1 Foundations
Expansive soils can damage foundations by uplift as they swell with increase in
moisture content. In addition, moisture content variations in expansive soil can
cause structural problems through differential movement of the structure. There
could be non-uniform movement in the structure if the moisture content and/or
soil type differs at various locations under the foundation. Sometimes, these
movements may be limited to a small area. These isolated movements of sections
of the structure can cause damage to the foundation, evidenced by cracking of the
slab or foundation, cracking in the interior or exterior wall faces, uneven floors
and/or misaligned doors and windows. This type of movement is generally related
with slab on grade construction. However, this type of movement may also occur
in structures with basements and crawlspaces.
Chapter 3
47
Another effect of expansive soils is additional horizontal pressure applied to
foundation walls found in basements and crawlspaces. Increased moisture in the
expansive soils adjacent to the foundation wall can exert tremendous force as they
expand and increase the lateral pressure applied to the foundation wall. If the
foundation wall does not have sufficient strength, minor cracking, bowing or
movement of the wall may occur. Serious structural damage to, or failure of, the
wall may also occur.
3.5.2 Retaining walls
Expansive soils often create long-term problems as backfill materials behind
retaining walls. The lumpy and cohesive nature of expansive soils often makes it
difficult to recompact them to states of uniform moisture content and unit weight
that will ensure minimal future settlements, minimum swelling potential or
minimum lateral earth pressures. Beyond the obvious problems of large and
Soil with additives (i) with addition of foam plastic � = 17 kg/m3 � = 66.6 kg/m3
2 4
2 4
50.0 42.0
37.5 25.0
24.4 36.4
432 62.1
(ii) with addition of porolon 21.5 6.0 91.0
3.7 Possible use of soil mixed with EPS beads
The discussion thus far shows the potential of using polymeric materials such as
tyres, fibres and foam chips for the treatment of expansive soils. In a similar
category, recycled EPS beads when mixed with expansive soils can be used for
varied applications as described in the ensuing sections.
Chapter 3
62
3.7.1 Backfill behind retaining wall
To avoid the failure of retaining walls located in expansive soil regions having
expansive clay as backfill, Petry and Armstrong (1989) suggested that the
expansive soil mass surface behind the retaining wall should be cut back to at
least 45 degrees from the horizontal and should be filled with non-active, free
draining material, such as clean granular sand or gravel, so that as it swells, it will
not impose loads on the wall. Furthermore, a system of weep holes and filter
protected drains are to be installed at the base of the wall in the backfill as shown
in Figure 3.11. This is because when clay backfill is compacted to a high dry
density and low moisture content, it develops high swelling pressures upon water
infiltration.
This process needs the free draining backfill to be imported from other areas.
Instead of filling with other soils, the expansive soils can be mixed with waste
EPS beads and compacted as lightweight fill.
Figure 3.11 Retaining wall backfill treatment (Petry and Armstrong, 1989).
3.7.2 Foundations
The differential movements in the foundations can be controlled by the use of
soil-EPS mixes. The in-situ expansive soils can be mixed with waste EPS beads
and can be compacted below the foundations. Through this way any isolated
movements can be taken care of by the EPS beads through elastic rebound nature.
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Chapter 3
63
3.7.3 Landfills
The use of EPS as a soil modifier is expected to enhance the property of clay
soils. That is the potential of swelling and shrinking can be reduced to make the
soils, which would otherwise be discarded, useful in applications such as
lightweight landfill cover materials. This may reduce the desiccation cracking in
compacted clay layers and reduce the leakage rates.
According to Mitchell and Saga (2005), the specific surface area of smectites
which are the predominant minerals in expansive soils, can be very large. The
primary surface area, that is, the surface area exclusive of interlayer zones, ranges
from 50 to 120 m2/g. The secondary surface that is exposed by expanding the
lattice so that polar molecules can penetrate between layers can be up to 840 m2/g.
Hence, to treat expansive soils, this surface area can be reduced by adding suitable
admixer(s).
It can be noted from the above studies that the reduction occurs with the addition
of admixers to expansive soils, either in combination or individually through both
mechanical and chemical means. In this context, any addition of material such as
sand, fibres, tyre chips etc., can reduce the surface area considerably through soil
replacement, which will lead to a reduction in swell pressure and swelling
deformation.
Therefore, within the context of the current study, it can be proposed that the in-
situ soil be modified with recycled EPS beads to reduce the surface area of the
clay.
3.8 Summary
Expansive soils are wide spread throughout the world. The main problem
associated with these soils is their swell-shrink potential. There are different
treatments options available for controlling these movements. However, each
method has certain limitations necessitating the need for further research using
alternative materials.
Chapter 3
64
As mentioned in Chapter 2, research elsewhere shows that EPS blocks can be
used as a compressible inclusion and EPS beads can be mixed with soils to
produce soil-EPS mixes with new characteristics for various geotechnical
applications. Based on the published results, a novel idea of mixing waste EPS
granules as a mechanical admixer with expansive soils was conceived. It was
hypothesised that by mixing EPS granules with expansive soils, the swell-shrink
potential will be reduced through partial soil replacement; decrease in unit weight
and also because of the cushioning effect of EPS through its elastic behaviour. In
addition, with clay replacement the reduction of surface area will cause a decrease
in swelling and shrinkage.
The new and innovative method of treating expansive soils with recycled EPS
provides an opportunity to use unwanted expansive soils and waste EPS in various
applications such as under footing, backfill behind a retaining wall and landfill
cover materials. With these points in view, a scoping study with dredged soil from
Brisbane River was performed. The findings were reported in the ensuing chapter.
65
CHAPTER 4 - SCOPING STUDIES WITH A DREDGED SOIL ___________________________________________________________
As indicated in Chapter 1, the current study was intended to investigate the
possibility of using recycled EPS beads as a swell-shrink modifier of expansive
soils. Chapter 2 presented various properties of EPS which may affect its
performance as a soil modifier. Chapter 3 described how the expansive soils can
cause serious damage to various structures and discussed the need to develop
appropriate method(s) to improve the soil characteristics. In this chapter, the
results of a preliminary investigation on the effects of EPS inclusion to a dredged
soil are described.
Early in this stage, it was realised that the soil to be tested should serve the
intention of observing the influence of EPS on heavy clays. While searching for a
suitable soil for this purpose in and around Brisbane, it was noticed that Port of
Brisbane Corporation was conducting dredging operations and begun placing the
dredged soil at Brisbane airport, for the filling the low-lying areas (Port of
Brisbane, 2001). The dredged soil was subsequently selected to start the
investigation on the effect of mixing recycled EPS beads. In subsequent chapters,
the resulting composite formed by Soil with EPS will be termed as SWEPS mix.
There are a number of reasons for the selection: i) similar soils have been studied
in the past, ii) the dredged soil is a waste material and its reuse would be
welcomed iii) the soil is a highly plastic clay and iv) the soil is available in huge
quantities and has not found practical use.
4.1 Dredged soils
Similar to the situations in many ports and harbours around the world, for
accessibility and to facilitate navigation of ships, Port of Brisbane conducts
regular maintenance and capital dredging activities. Because the sediments are
usually dredged from the bottom of water bodies, dredged soil contains high water
content in the range of 500 to 1000 % (Kamon et al., 2000). In addition,
depending on the proximity to the sources of pollution such as industrial or
municipal as well as urban and agricultural non-point discharges, it also contains
contaminated sediments and/or organic matter. Consequently, this is considered as
Chapter 4
66
a waste material and its disposal is one of the challenges due to the strict
environmental regulations.
Traditionally, the most common and least expensive disposal of the dredged soil
is open-water disposal. However, the pollutants present in the dredged soil often
can cause detrimental environmental impacts to the ecology of water bodies.
Hence, this method of disposal is restricted with the introduction of national and
international laws (Millrath et al., 2002). The permissible and threshold limits for
the disposal of the dredged soil to water bodies and land disposal vary
considerably. In Australia these are governed by ANZECC (1992) guidelines. The
strict implementation of these environmental laws has driven up the cost of
disposal.
Owing to the availability of the dredged soil in huge quantities and the shortage of
good quality material for various construction purposes for economic
development in the coastal areas, the use of uncontaminated dredged soil as a
construction material has a strong economical advantage in the aspect of the
reutilisation of waste matter. In view of this, ports worldwide try to use a
multifaceted approach including disposal, recycling, separation, dewatering,
stabilisation, decontamination and reuse of the dredged soil (Millrath et al., 2002).
The use of dredged soils in construction has dual advantages. Firstly, it reduces
the need for importing soil at high transporting cost and secondly, it increases the
life span of disposal sites by reducing the waste flow (Tsuchida et al., 2001).
Dredged soil comprises mainly of clays, silts and sand mingled with rocks and to
some extent organic matter. The properties of marine soils that are most
commonly dredged for maintenance purposes are given in Table 4.1.
Dredged soils are usually soft and compressible which renders them ineffective
for use in their native state. Consequently, the use of dredged soils as a structural
fill requires a significant reduction in moisture content and an increase in
workability. This is because with its high moisture content, the strength,
compressibility and durability of the material may be unsatisfactory (Wiley III et
al., 2002).
Chapter 4
67
Table 4.1 Properties of marine clay at different locations of the world.
1Ahmad and Peaker (1977); 2Fang and Owen (1977); 3Katti et al. (1977); 4Rajasekaran and Rao (1998); 5Minegashi et al. (2002); 6Bergado et al. (1996); 7Satoh et al. (2001); 8Miura et al. (1987); 9Mohan and Bhandari (1977); 10Tsuchida et al. (1996) ; 11Yoonz et al. (2004).
There is evidence that cementing additives can effectively improve some of the
mechanical properties of dredged soils, such as resistance to compression,
improvement in strength and durability (Ogino et al., 1994; Gulin and Wikstrom,
Natural water content (%)
Liquid limit (%)
Plastic limit (%)
PI (%)
Particle density (t/m3)
Silt (%)
Clay (%)
Singapore marine clay1 50-83 50-90 18-22 30-50
James Bay marine clay(Canada)1
22-38 26-38 14-18 5-18
Leda clay Ottawa(Canada)1 28-50 20-45 18-24 5-20
Norwegian soft clay1 27-40 25-36 17-20 6-20
Gulf of Mexico2 72 34
Gulf of Amine2 163 121 51
Bombay (M1)3 80-100 65-75 20-25 25-35 35-55
(M2)3 80-100 50-70 25-40 20-45 40-65
(M3)3 60-100 55-85 25-40 15-30 60-80
(M4)3 60-125 60-100 30-55 10-40 35-75
Madras clay (India)4 88 33
Kanto Loam (Japan)5 116.5 143.7 74.8 2.81
Soft Bangkok clay6 76-84 103 43 60 28 69
Dredged Ariake clay, Japan7
2.5 m depth8
6.5 m depth8
10.5 m depth8
84 162 122 108
63.8 125 97 79
26.9 55 43 39
36.9 70 54 40
2.69
Visakhapatnam (India)9
80-90
65-97
40-45
24-55
2.65
40-70
Kandla (India)9 35-75 55-80 20-35 20-50 2.72 30
Willingdon, Cochin (India)9 75 109 40 69 2.52 53
Tokyo Bay mud10 100.4 38.9 41.3 24.5
West-Southern part of Korea11
132 45 24 21 2.66 93
Chapter 4
68
1997; Hoikkala et al., 1997; Den Haan, 1998; Tremblay et al., 1998; Kamon et al.,
2000).
In chemical treatments, special machineries are needed which cause the cost per
unit volume of the treated soils to become prohibitive. To make treated soils more
competitive to conventional fills it is necessary to find their value added
properties. The addition of lightweight soil additives such as EPS and airfoam is a
good option for commercially viable reuse of dredged soils since lightness is a
property effective to increase the economic efficiency (Okumura et al., 2000).
As discussed in Chapter 2, the use of EPS beads with dredged soil was
investigated in Japan for port and harbour structures and for construction surplus
soil (Miki, 1996; Hirasawa et al., 2000; Okumura et al., 2000; Yamane et al.,
2000; Satoh et al., 2001; Tsuchida and Kang, 2003; Yoonz et al., 2004). In these
studies, moisture content was in the order of 2.5 times the liquid limit and pre-puff
EPS beads were used for mud dispersion, to adjust the unit weight and to enhance
the workability of the composite thus formed (Tsuchida et al., 2001; Satoh et al.,
2001).
The current scoping study was intended to consider the limiting factors that affect
the placing and/or compaction and the miscibility of crushed waste EPS beads and
soil for land applications. In contrast with the earlier studies, EPS was mixed at a
moisture content that is close to the optimum moisture content of the dredged soil
to achieve better strength and compressibility characteristics.
4.2 Waste EPS
In the current research, crushed EPS pieces from produce-boxes were collected
from an EPS collection centre situated in Archerfield, Brisbane. This is one of six
EPS reprocessing sites in Queensland and forms a part of the national EPS
reprocessing network in Australia (PACIA, 2005).
The produce boxes before and after crushing at the collection centre is shown in
the Figure 4.1a and 4.1b. The recycled EPS vary in size from what is shown in
Figure 4.1b to that shown in Figure 4.2b. Based on a preliminary testing, it was
Chapter 4
69
observed that large EPS pieces as shown in Figure 4.1 (b) were difficult to mix
and compact in a standard compaction mould. Moreover, large EPS pieces would
have higher compression on loading and showed some rebound tendency upon
unloading; hence, the particle size in the range of 1.2 mm to 9.5 mm was selected.
Even though different produce boxes were available at the EPS collection centre,
for the present research produce boxes of the same type were used. The mean
density of the EPS pieces is 20 kg/m3.
In the laboratory, the larger EPS pieces were crushed in a blender to obtain 90%
of the particles within the range of 1.2 mm to 9.5 mm. While most of the recycled
EPS beads from packaging boxes may have the different properties, as an added
precaution and to avoid any material variability that would have arisen from using
different batches of crushing, in the current research, all the recycled EPS beads
were obtained from the same batch.
The recycled EPS used in this study was of non-fire retardant type. Generally, for
packaging products flame retardants are not used as additives because it will
increase the cost of production (Horvath, 1995).
(a) (b) Figure 4.1 Produce boxes (a) before crushing and (b) after crushing.
The shape and relative size of the pre-puff EPS beads and recycled EPS beads are
illustrated in Figure 4.2a and 4.2b, respectively. As can be seen from these
figures, in contrast with the pre-puff EPS beads, the recycled EPS beads varied in
size considerably and were irregular in shape. Note that pre-puff EPS beads were
used in the earlier studies (Tsuchida et al., 1996; Satoh et al., 2001; Minegashi et
Chapter 4
70
al., 2002; Yoonz et al., 2004) and mixed with dredged soils to form lightweight
flowable fill materials.
(a) (b) Figure 4.2 Size and shape of the EPS beads
(a) pre-puff beads and (b) recycled beads.
The particle size distribution curve of the recycled EPS beads is shown in Figure
4.3. The mean diameter D50 of the recycled EPS particles is 4.5mm.
0
20
40
60
80
100
0.01 0.1 1 10 100Particle size , mm
Per
cen
tag
e fin
er
Figure 4.3 Particle size distribution curve recycled EPS beads.
4.2.1 Effect of temperature on EPS
According to AS 1289.2.1.1 – 1992, for moisture content determination by oven
drying method, soil samples have to be kept in an oven for 24 hours at 105°C.
Hence, prior to determining the moisture contents of soil-EPS mixes, the
influence of temperature on the mass and volume of EPS beads was investigated.
Chapter 4
71
For this purpose, three sizes (10, 20 and 30 mm side) of EPS cubes were prepared
by hot wire cutting from EPS blocks. All the specimens were tested at 105°C ±
2°C for a duration of 24 hours as per the standard specification.
As explained in Chapter 2, evidence suggests that the highest service temperature
that EPS can withstand is 70°C (Table 2.2). Furthermore, EPS will melt at 93°C
and start flowing away from flame at around 120°C (Thompsett et al., 1995).
However, the effect of temperature variation on EPS dimension and mass had not
been satisfactorily explained in the past. Hence, it was decided that in the present
investigation, the effect of temperature variation from 40 to 100°C should be
considered.
Table 4.2 Effect of temperature on mass and volume of EPS cubes.
Side Dimensions, mm Mass, g
Before heating
After 24 hr heating at temperatures of
Before heating
After heating
40 - 70°C* 80°C 100°C 40 -100°C**
10 10 0.7 0.3 0.02 0.02
20 20 1.4 0.6 0.16 0.16
30 30 2.1 0.9 0.54 0.54
Volume reduction, %
0 65.7 97.3
Note: *within this range the dimensions are unaltered. **within this range the mass is constant. Table 4.2 shows the test results, which indicate that temperature does not affect
both the volume and mass of the EPS cubes up to a temperature of 70°C.
However, it is seen that under temperatures of 80°C or higher the EPS cubes
experienced volumetric changes. Note that up to 80° C the reduction in size was
relatively uniform and hence the cubical shape was always retained (Figure 4.4).
This could be because the EPS contains nearly 98% voids by volume filled with
gas (Horvath, 1995). The gas entrapped in the voids of EPS beads would be stable
up to 70°C but starts to escape at temperatures greater than 70°C. This would
transform the EPS bead into a polystyrene bead.
Chapter 4
72
Even though the size and volume of the cubes were changed at a temperature of
80°C or higher (Figure 4.4), the mass remained unaltered. This is an important
observation, since for calculating the moisture contents and subsequently the dry
unit weight of the soil-EPS mix; the sample has to be kept in the oven at 105°C.
Initial side dimension (i) 30 mm (ii) 20 mm (iii) 10 mm
Figure 4.4 Reduction in size of specimens before and after heating at 80°C. 4.3 Dredged soil from Port of Brisbane
The characteristics of the dredged soil, tested as per the relevant Australian
Standards are summarised in the Table 4.3, which are in agreement with most
marine soils found around the world (Table 4.1). The compaction curves
(Standard and modified) for the dredged soil are shown Figure 4.5. This
compaction standard was adopted for all the tests in this scoping study.
Standard compaction
Modified compaction
8
10
12
14
16
18
0 10 20 30 40 50 60
Moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 4.5 Compaction curves for the dredged soil tested.
Chapter 4
73
Table 4.3 Characteristics of the dredged soil.
4.4 Preparation of dredged soil and EPS mix
For performing tests with dredged soil-EPS mix, the specimens were prepared in
the following mix procedure. As the natural moisture content of the dredged soils
was 80%, it was brought down to slightly below the optimum moisture content by
air drying. Subsequently, tap water at room temperature was added to the soil to
bring the moisture content to the desired values. Then these samples were cured
for 7 days in a sealed zipper bag. Thereafter, the recycled EPS beads were mixed
to this moist soil in different proportions using a bench top Hobart mixer. A
photograph of the dredged soil at 45% moisture with 2% of recycled EPS beads
Location number and name Country LL Pl PI 41 Echuca, Victoria19 Australia 63.0 25.0 38.0 42 Poona1 India 81.5 43.2 38.3 43 Malaprabha1 India 74.0 34.0 40.0 44 Quail creek, Arlington9 USA 69.0 28.0 41.0 45 South cooper estate East,
Arlington9 USA 71.0 29.0 42.0
46 Nasr City11 Egypt 76.0 34.0 42.0 47 Werribee, Victoria19 Australia 74.0 32.0 42.0 48 Walnut creek, Arlington9 USA 69.0 43.0 49 South cooper estate West,
Arlington9 USA 74.0 29.0 45.0
50 Degirmenlik4 Cyprus 67.8 22.2 45.6 51 Belgaum soil 12 India 65.0 19.0 46.0 52 San Antonio7 USA 73.0 27.0 46.0 53 Bryan, Texas15 USA 68.0 20.0 48.0 54 Nasr City11 Egypt 80.0 28.0 52.0 55 Vijayawada1 India 91.8 38.3 53.5 56 Irving7 USA 82.0 27.0 55.0 57 Ravenhall, Melbourne,
Soil 220 Australia 103.0 47.0 56.0
Sources: 1Katti and Katti (1994); 2Rao et al. (2001); 3Sahu (2001); 4Nalbantoglu and Gucbilmez (2002); 6Puppala et al.(1996); 7Puppala and Musenda (2000); 8Punthutaecha et al. (2006); 9Puppala et al. (2003); 10Bao and Liu (1988); 11El-Sohby et al. (1988) ; 12Fan and Yang (1988) ; 13Li and Zhao (1988) ; 14Liu et al. (1988); 15Rauch et al. (2002); 16Kalkan and Akbulut(2004); 17Basma et al. (1998); 18Al-Homoud et al. (1995); 19Kodikara et al. (2002); 20Jayasekara and Mohajerani (2001); 21Jones et al. (2001)
1/3 of locations
1/3 of locations
1/3 of locations
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Location number with reference to Table 5.1
Pla
stic
ity in
dex,
%
Figure 5.1 Variation of plasticity index at different locations around the world.
Chapter 5
97
5.2 Material properties
5.2.1 Fine Sand
Commercially available fine white sand labelled as W9 supplied by Riversands
Pty Ltd., Brisbane was used. The sand is sub-angular silica sand and classified as
poorly graded clean fine sand (SP) according to Unified Soil Classification
System (AS 1726, 1993). Its specific gravity is 2.65. Greater than 95 percent of
the sand particles passes through no. 30 sieve (0.420 mm) and less than 5 percent
passes the no.200 sieve (0.074 mm).The particle size distribution curve for sand is
plotted in Figure 5.2. The uniformity coefficient Cu (= D60/D10), the effective
diameter D10 and the mean diameter D50 of the sand are 1.53, 0.17 mm and 0.24
mm, respectively.
0
20
40
60
80
100
0.01 0.1 1 10Particle size, mm
Per
cen
tage
fin
er
Figure 5.2 Particle size distribution curve for sand.
5.2.2 Bentonite
Bentonite, a very highly plastic and swelling clay mineral, refers to any material
that is primarily composed of the montmorillonite group of minerals formed by
the chemical weathering of volcanic ash and whose physical properties are
dictated by the montmorillonite minerals (Grim and Guven, 1978). Basically,
bentonite is a sodium montmorillonite clay in which mica-like layers are bonded
together by sodium ions. Smectite is the family name of montmorillonite and
bentonite (Tsai, 1993). According to Mitchell and Soga (2005), bentonite is a
highly colloidal and expansive clay that may have a liquid limit of 500 percent or
more. Characteristics of montmorillonite minerals include large cation exchange
Chapter 5
98
capacity, large specific surface area, high swelling potential and low hydraulic
conductivity to water (Gleason et al., 1997)
In the current study, commercially available powdered natural sodium-rich
bentonite supplied by Unimin Australia limited, Brisbane was used. This
bentonite came from Miles, which is 350 kilometres west of Brisbane,
Queensland, Australia.
The physical properties of the bentonite are shown in the Table 5.2. The
generalised X-ray diffraction plot and mineralogy of the bentonite used in the
present study are shown in Figure 5.3 and Table 5.3 respectively (Gates et al.,
2002).
Table 5.2 Properties of bentonite.
Trade name Trubond
Source Miles, Queensland, Australia
Type Sodium bentonite Retained on 75 �m (Wet screen) Passing 2 �m (XRD Analysis)
2% 80%
Bulk density 0.9 t/m3
Liquid limit 400%
Plastic Limit 41%
Moisture content (as supplied) 11%
Cation exchange capacity 85 meq/ 100 g
Table 5.3 Mineralogy of Miles bentonite (Gates et al., 2002).
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Chapter 5
99
Figure 5.3 X-ray diffraction plot of the bentonite used in the study. S = Smectite, M= Mica, S/M = Smectite/ Mica, Q= Quartz, C = Cristobalite / opal, F= Feldspar
(Gates et al., 2002).
5.3 SB mix preparation
The designated amount of bentonite powder was added to the dry sand by dry
weight basis, e.g. 10% bentonite content refers to addition of dry bentonite
amounting 10% of the weight of dry sand. These two materials were then
thoroughly mixed by hand several times until a fairly uniform and consistent
mixture was obtained. Distilled water was subsequently added in the required
quantity in increments and the mixture was worked by hand for about 15 minutes.
Based on visual observation of the mixture and upon satisfying that the moisture
had been distributed evenly all over the mixture, the samples were then sealed into
plastic containers and placed in a humid chamber for at least 14 days to reach
moisture equilibrium before being subjected to various tests.
5.4 Atterberg limits
As mentioned earlier, in preparing reconstituted soils, the aim was to obtain soils
potentially with plasticity index (PI) in the range of 20 to 35% (corresponding to
low PI), 35 to 50% (corresponding to intermediate PI) and >50% (corresponding
to high PI). For that purpose Atterberg limit tests were conducted on four different
preliminary mixtures prepared by adding dry bentonite of 10%, 20%, 30% and
40% of the dry mass of sand. These tests were performed according to
AS1289.3.1.1 – 1995 and AS1289.3.2.1-1995 for liquid limit and plastic limits,
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Chapter 5
100
respectively. The variations of the liquid limit and plastic limit are shown in
Figure 5.4.
Liquid limit
Plastic limit
0
50
100
150
200
250
300
350
400
450
0 20 40 60 80 100Bentonite. %
Liqu
id li
mit,
Pla
stic
lim
it, %
Figure 5.4 Liquid limits and plastic limits for sand-bentonite mixes.
It is well known that clay particles, due to their very large specific surface area,
form a cohesive membrane around coarser particles. This prevents direct contact
among coarser particles, i.e. the coarser particles become embedded in a matrix
provided by the clay particles (Pandian et al., 1995).
Seed et al. (1964) mentioned that the liquid and plastic limits of a soil are
primarily controlled by its clay content. Therefore, the increases in these indices
are expected as clay content increases due to the addition of bentonite. However,
the influence of bentonite, as shown in Figure 5.4, is more significant on the
liquid limit than the plastic limit. Liquid limit shows an approximately curvilinear
increment whereas plastic limit shows a linear increment. This is in agreement
with the results reported by deMagistris (1998) and Montanez (2002).
In the current study, the liquid limit increases from 33 to 84% with an increase in
bentonite content from 0% to 40%. While Pandian et al. (1995) showed a linear
relationship for sand-bentonite mixtures, the liquid limit variation shown in Figure
Chapter 5
101
5.4 exhibits a non-linear trend. These differences may be attributed to the method
of proportioning sand and bentonite for the mixes. Pandian et al. (1995) prepared
the mix by adding bentonite into the mix to replace the same quantity of sand.
However, in the current study, bentonite was added by the dry weight of sand, i.e.,
for a fixed quantity of sand, different bentonite contents were added.
With regards to the variation of plasticity with bentonite content, Montanez
(2002) observed that for a uniform sand, the plastic limit shows a slight and
almost negligible increase. The same were observed in the current research. That
is the plastic limit increased slightly from 17% to 24% with an increase in
bentonite content from 10% to 40%.
By systematically analysing the Atterberg limits of these preliminary mixtures,
bentonite contents of 16%, 24% and 32% were found to produce reconstituted soil
mixes with a plasticity index (PI) of 22%, 38% and 53%, respectively (Figure
5.5). These reconstituted clays (SB16, SB24 and SB32) were classified as CI, CH
and CV, respectively (Figure 5.6).
0
10
20
30
40
50
60
10 15 20 25 30 35
Bentonite, %
Pla
stic
ity In
dex
, %
Figure 5.5 Variation of plasticity index with bentonite content.
Chapter 5
102
With the % bentonite values used and the resulting PI values, the activity of each
mix, defined as PI ÷ (% clay < 2 �m), can be calculated (see Table 5.4) and
plotted on the Williams and Donaldson chart (1980) (Figure 5.7) to predict the
expansion potential of the mixes. It is seen that with 16, 24 and 32% bentonite
content the mixes can be separated into three distinct expansion potentials. Hence,
these reconstituted expansive soils were used as test soils for the subsequent tests
like swelling, shrinkage, shear behaviour, hydraulic conductivity, desiccation etc.,
which are described in ensuing chapters.
Table 5.4 Bentonite content and mix properties.
Mix % passing 2 �m (by mass of
dry sand)
Liquid Limit,
%
Plastic Limit,
%
Plasticity Index,
%
Activity,
)%( clayPI
SB16 12.8 43 21 22 1.72
SB24 19.2 60 22 38 1.98
SB32 25.6 77 24 53 2.07
Figure 5.6 Plasticity chart for the sand-bentonite mixtures (BS 5930, 1999).
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Chapter 5
103
SB32
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70Clay content (% <0.002mm)
Pla
stic
ity In
dex,
%
Figure 5.7 Expansion potential of sand-bentonite mixes as predicted by the chart of
Williams and Donaldson (1980).
5.5 Hygroscopic moisture content
Bentonite powder, because of its water adsorbent nature, always contains some
hygroscopic moisture content. When the bentonite was added to oven dried sand,
this moisture content contributed to the overall moisture content. In preparing
reconstituted soils of known moisture content the hygroscopic moisture content of
bentonite fractions (Table 5.5) was accounted for. The hygroscopic moisture
content was determined according to AS 1289.2.1.1, 1992.
Table 5.5 Variation of hygroscopic moisture content.
Bentonite fraction,
%
Hygroscopic moisture content,
% 0 0
16 1.35
24 1.82
32 2.50
100 11.0
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Chapter 5
104
5.6 Compaction behaviour
As mentioned in Chapter 2 and 3, it was decided to study the influence of recycled
EPS beads on the swell-shrink of expansive soils at soils optimum moisture
content. For that purpose, compaction characteristics of the reconstituted soils
were studied. The influence of EPS on compaction characteristics of soils will be
described in Chapter 6. The typical compaction curves of sand-bentonite (SB)
mixes are shown in Figures 5.8, 5.9 and 5.10 for SB16, SB24 and SB32,
respectively.
SB16
Zero air voids line
Compaction curve
14
15
16
17
18
0 5 10 15 20 25 30 35Moulding moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 5.8 Compaction curve for SB16.
As expected, in each compaction curve, the dry unit weight of the composite
increases with increasing moulding moisture content and after attaining optimum
moisture content, the dry unit weight decreases with further increase in moisture
content. The resulting Optimum Moisture Content (OMC) and Maximum Dry
Density (MDD) are presented in Table 5.6.
Chapter 5
105
SB24
Zero air voids line
Compaction curve
14
15
16
17
18
0 5 10 15 20 25 30 35Moulding moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 5.9 Compaction curve for SB24.
SB32
Zero air voids line
Compaction curve
14
15
16
17
18
0 5 10 15 20 25 30 35
Moulding moisture content, %
Dry
uni
t wei
ght,
kN/m
3
Figure 5.10 Compaction curve for SB32.
It has been frequently reported elsewhere that noticeable change in compaction
characteristics of sands can result with the inclusion of bentonite. Ambrosanio
(1955, as cited in deMagistris, 1998) and Kenny et al. (1992) reported that for
Chapter 5
106
uniform fine sands, as used in the present study, there is an increase in dry unit
weight with an increase in bentonite content up to a certain optimum percentage
and then dry unit weight starts to decrease. deMagistris (1998) attributed the
increase in dry unit weight to the reduction of voids in uniform sand by bentonite
addition up to a certain extent. The result from the current study is also in
agreement with the above observation and shown in Figure 5.11.
Table 5.6 Maximum dry unit weight and optimum moisture content of SB mixes.
Flyash9 Rubber and bentonite Decreased No much variation
Black cotton soil, India (CH)10
Geotextile woven fabric (0.5 mm diameter) Fibre glass pieces (0.1 mm diameter)
Increase Decrease
Clay11 Polypropylene fibres No much variation
No much variation
Decomposed granite12
Heat compressed and crushed EPS (HCCE)
Decreases No variation
1Setty and Rao (1987); 2Setty and Murthy (1990); 3Fletcher and Humphries (1991); 4Maher and Ho (1994); 5Al-Wahab and El-Kedrah (1995); 6Kumar et al. (1999); 7Kaniraj and Gayathri, (2003); 8Zhang et al. (2003); 9Cocka and Yilmaz (2004); 10Gosavi et al. (2004); 11Miller and Rifai (2004); 12Yasufuku et al. (2002).
Chapter 6
124
Figure 6.7 Compaction curves of decomposed granite mixed with HCCE
(after Yasufuku et al., 2002).
In the present investigation, the decrease in dry unit weight with the addition of
recycled EPS beads is in agreement with other lightweight recycled materials or
fibres. However, in terms of OMC, the results of the current study show that
OMC is not sensitive to the change of material composition. This is because EPS
is very light in weight than the other recycled materials.
6.8 Volumetric proportions
It was expected that with the addition of recycled EPS beads there would be
reduction in the volume of soil in the composite. To understand the volumetric
proportions of soil and EPS within the composite material, tests were conducted
on the dry EPS beads to find the dry unit weights of EPS in loose and compacted
(with standard energy) conditions.
It was observed that in a loose state the dry unit weight of recycled EPS beads
alone was 0.16 kN/m3, whereas after compaction in a standard compaction mould,
the dry unit weight increased to 0.19 kN/m3. This increase in unit weight could be
attributed to the compression of EPS beads and reduction in voids during
compaction. These values indicated that the method of placing and compacting
influenced the dry unit weight of the EPS beads. These values further indicated
that the standard compaction produced a decrease in the volume of EPS beads of
13.5%.
Chapter 6
125
The calculation of volumetric proportions were based on the assumption that the
mass of each component of the composite would have reached their respective
unit weight had they been individually compacted using standard compaction as
illustrated in the Figure 6.8. That means that the maximum dry unit weight of the
soil is at its corresponding optimum moisture content and the dry unit weight of
EPS beads could at its compacted state.
The reduction in dry unit weight of the composite with the addition of recycled
EPS beads was therefore calculated based on the following considerations.
• The maximum dry unit weight of compacted EPS was achieved.
• The maximum dry unit weight of soil at its optimum moisture content under
standard compaction was considered. It varied with the bentonite content
added to the soil (Table 5.5).
• Compactive effort was the same for both soil and SWEPS mix. Standard
compactive effort was followed as per standard.
• The volume of soil was calculated based on its mass in the SWEPS mix. Then
EPS volume was the difference between composite volume and soil volume.
(a) Composite (b) Individual material
Figure 6.8 Soil – EPS volumes (a) as a composite (b) as individual components.
Volume of EPS in all the soils is based on the following equations
SoilCompEPS VVV −= (6.1)
Chapter 6
126
Where VEPS is volume of EPS, %
Vcomp is volume of SWEPS mix, % (this is expressed as 100%)
Vsoil is volume of available soil, %, it is calculated based on Equation 6.2
Soil
SoilSoil
WV
ρ= (6.2)
Where Wsoil is the dry mass of soil in the composite, kg
soilρ is the maximum dry density of soil at its optimum moisture content,
kg/m3
Figure 6.9 shows the volume occupied by the EPS in SWEPS mix at 0.3, 0.6 and
0.9% of EPS for soils with bentonite contents of 16% (SB16), 24% (SB24) and
32% (SB32).
0
5
10
15
20
25
30
0 0.2 0.4 0.6 0.8 1EPS, %
Vol
ume
of E
PS
in S
WE
PS
mix
es, %
SB16SB24SB32
Figure 6.9 Generalised volumes of EPS in SWEPS mix at different % of EPS by
dry weight of soil.
The fitting line is linear and passes the origin. The regression coefficient (r2) is
0.998. At 0.3 % by dry weight of soil the EPS occupies 7.5% of the volume and at
Chapter 6
127
0.6% it occupies nearly 15.5% and finally at 0.9% by dry weight it occupies
22.25% of the total volume.
This addition of EPS will decrease the unit weight of the SWEPS mix as
discussed earlier. However, the strength of the mix has to be carefully considered
in the design of mix proportions for the SWEPS mix. If required, stabilisers may
be used to compensate the loss of strength due to the addition of EPS.
6.9 Predictive model for dry unit weight
The dry unit weight behaviour of SWEPS mixes was examined by focussing on
the influence of the soil type (PI of 22, 38 and 53%) and EPS content (0.0, 0.3, 0.6
and 0.9%).
The experimental data was quantitatively analysed by multiple regression models
by correlating dry unit weight with PI and EPS. The equation obtained from the
multiple regression analysis is
EPSPId 91.4013.068.17 −−=γ (6.3)
Where dγ is dry unit weight, kN/m3,
PI is plasticity index, %
EPS is quantity of EPS, %
This equation is valid only for the range of soils tested and for EPS contents
evaluated. The validity of this equation was checked and a comparison was made
between the measured and predicted values for the dry unit weight as shown in
Figure 6.10. Figure 6.11 shows the experimentally obtained dry unit weight vs.
the predicted values. The regression analysis of this prediction models gives R2
value of 0.9858.
Chapter 6
128
12
13
14
15
16
17
18
19
15 20 25 30 35 40 45 50 55
Plasticity index, %
Dry
uni
t wei
ght,
kN/m
30.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
Figure 6.10 The relation between the PI and the measured and predicted values of
dry unit weight.
R 2 = 0.9858
10
15
20
10 15 20Actual dry unit weight, kN/m3
Pre
dict
ed d
ry u
nit w
eigh
t, kN
/m3
Figure 6.11 The relation between measured and predicted dry unit weights.
6.10 Summary
The overall compaction behaviour of SWEPS mixes is presented in this chapter.
Three EPS contents of 0.3%, 0.6% and 0.9% were added to the test soils and
compacted according to standard Proctor compaction method. It was observed
that the addition of EPS reduced the dry unit weight. This reduction in dry unit
weight can be attributed to the specific gravity of the recycled EPS beads. In
Chapter 6
129
addition, the resistance offered by EPS (elastic rebound) can reduce the
compactability of the mix at higher EPS contents.
It was also observed that the shapes of SWEPS compaction curves were similar to
that of the control soils but with reduced maximum dry unit weight values. On
volumetric proportions it has been shown that for the given soil at the maximum
possible mixing rate of 0.9% by dry weight, recycled EPS occupy 22.25% of the
total volume of the mix.
Increasing the compaction energy can increase the dry unit weight of the SWEPS
mixes owing to the compression of EPS beads and also due to the limitation in the
inclusion of the EPS beads due to reduced moisture content at higher compactive
energies.
It has been demonstrated that the inclusion of EPS into a soil can significantly
reduce the dry unit weight of the composite thus formed. In the field, EPS mixing
and compaction can be performed at optimum moisture content of the soil. The
lightweight characteristics of the SWEPS suggest that the material may be
suitable for use as a lightweight backfill. The use of SWEPS behind a retaining
wall is expected to reduce the lateral thrust on the wall, which will in turn result in
a more economical wall design.
Following these compaction studies, keeping in view with the main focus of this
research, a series of swelling and shrinkage tests were performed on the SB and
SWEPS mixes at their respective MDD and OMC conditions. The following
chapter discuss the outcome of those experiments.
Chapter 6
130
131
CHAPTER 7 – SWELLING AND SHRINKAGE STUDIES ON SWEPS MIXES
As discussed in Chapter 3, the prominent feature of expansive soils is their swell-
shrink potential due to moisture changes. This feature is considered as an
important factor in geotechnical design because it often causes unpredictable
ground movements. The swell of soil is due to formation of a moisture film
around the soil particles as a result of reaction between the clay particles and
water (Low, 1992). Even though swelling can occur due to load reduction, the
problem of swelling is more severe with water imbibition (Sivapulliaiah et al.,
1996).
As mentioned in Chapters 1 and 2, an attempt was made to mix recycled EPS
beads with reconstituted expansive soils in assessing their potential as a swell-
shrink modifier. Based on the compaction characteristics described in Chapter 6, a
series of free swell tests, swell pressure tests, and shrinkage tests were performed
to investigate the relationships between swell-shrink characteristics and EPS
contents of the SWEPS mixes at their maximum dry unit weights and optimum
moisture contents. The three test soils (SB16, SB24 and SB32) and four EPS
contents (0%, 0.3%, 0.6% and 0.9%) were investigated further in this study.
In this chapter, the specimen preparation techniques and test procedures are
outlined together with the test results and discussion on swelling, cyclic swelling
and reduction in swelling. Furthermore, the effects of recycled EPS beads on the
axial, diametral and volumetric shrinkage of expansive soils are also described.
7.1 Compaction of SWEPS specimens
While EPS block can be cut using either a fine-blade saw or a hot-wire apparatus
(Horvath, 1995), the nature of sand and bentonite mixes in the present research
does not allow sawing following compaction. Furthermore, it is also very difficult
to perform hot-wire trimming. Hence, static compaction method was selected for
preparing specimens for swelling, consolidation, suction, desiccation and
hydraulic conductivity tests.
Chapter 7
132
In static compaction, the soil sample is compacted by a gradually applied
monotonic force. Venakatarama Reddy and Jagadish (1993) have described two
types of static compaction. They are the constant peak stress – variable stroke
compaction method and the variable peak stress – constant stroke compaction
method.
In the constant peak stress – variable stroke compaction method, the applied stress
is gradually increased at a defined rate until a specific peak stress is reached. The
thickness of the compacted specimen depends on the moisture content. While the
resulting compaction curves are similar to those of dynamic compaction
procedure, the energy input varies with the moisture content.
In the variable peak stress – constant stroke compaction method, a static force is
gradually applied until a specific final thickness corresponding to the required
volume is achieved. In this case the energy input is variable but can be derived
indirectly and specified if necessary (Montanez, 2002).
The variable peak stress – constant stroke compaction method was used in the
current research to obtain specimens with constant initial thickness. A layer of
cling film (plastic wrap) was placed over the piston during the compaction process
in order to stop the compacted material from adhering to the top piston.
7.2 Swelling Characteristics of SWEPS mixes
7.2.1 Common test procedures
The most common methods for determining the magnitude of swell in soils
involve the use of conventional one-dimensional consolidation (oedometer)
apparatus. A wide variety of test procedures have been used in the past as
summarised by Nelson and Miller (1992). However, basically there are two test
types available for finding the free swell and swell pressure of the soil. They are
referred to as the “free swell” (also called “vertical swell” or “swell deformation”
or “swell strain”) test; and the “swell pressure” (also called “constant volume”)
test (Sridharan et al., 1986). In this thesis, the terms “free swell” and “swell
pressure” as prescribed in ASTM D 4546-96 are used.
Chapter 7
133
In the free swell test, the specimen is allowed to swell under a seating pressure,
generally 6.9 kPa (1 psi), by submersion in distilled water. After attaining an
equilibrium condition, the specimen is then loaded and unloaded following the
conventional oedometer test procedure. Through this procedure the magnitude of
both free swell and swell pressure can be obtained from the same soil specimen.
In contrast, in the constant volume test, the applied load is gradually increased in
order to keep the specimen’s volume unchanged after being submerged in distilled
water. The final load at which no further deformation occurs is taken as the swell
pressure.
Gilchrist (1963, cited in Nishimura, 2001) stated that the swell pressure obtained
from the free swell test was different from that obtained from the constant volume
test. However, other researchers (Borgesson, 1990; El-Sohby, 1994) obtained
comparable results in magnitude of swell especially at high density.
Notwithstanding this discrepancy, both the free swell and the swell pressure tests
were performed in the current study to reflect the two different test conditions.
7.2.2 Specimen preparation
According to El-Sohby and Rabba (1981), Yevnin and Zaslavsky (1980), initial
moisture content and initial dry unit weight are important factors affecting the
swell behaviour of expansive soils. In the present investigation, the specimens
were produced at their estimated maximum dry unit weight and at their
corresponding optimum moisture content as obtained in Chapter 6. The required
amount of SWEPS mixes were compacted statically in a conventional oedometer
ring using variable peak stress – constant stroke compaction method as described
in Section 7.1, until the desired dry unit weight corresponding to the standard
Proctor compactive effort was achieved.
The stainless steel oedometer ring was 70 mm in diameter and 19 mm in height.
Silicone grease was smeared on the inside of the ring before compaction to reduce
the side friction between the ring and soil mix specimen. To control the dry unit
weight, the specimens were compacted statically using a hydraulic jack as shown
in the Figure 7.1.
Chapter 7
134
Figure 7.1 Diagrammatic representation of static compaction of oedometer
specimen.
The oedometer ring with top clamping ring was positioned and screwed on to a
base plate (fixed ring type). Then the desired amount of SWEPS mix was placed
inside the ring and the assembly was positioned under the hydraulic jack. The
specimen was compacted in three equal layers to maximise the overall uniformity
and each layer was scarified before compacting the next layer for proper bonding.
After compaction, the ring was released and placed in the oedometer cell with air-
dry porous stones on top and bottom of the specimen. To protect the porous stones
from soil contamination, a filter paper was placed between the specimen and the
porous stone on both ends. Subsequently, the entire assembly was positioned in
the loading frame and the deflection reading was adjusted to zero. The specimen
was subsequently inundated with distilled water.
7.2.3 Test procedure
Vertical loading was applied using a Wykeham-Farrance oedometer loading frame
(Bishop type, rear loading, lever arm bench model). The free swell test method
was used to determine the swelling deformation of the specimens (AS 1289.7.1.1-
2003) and constant volume test was chosen for swell pressure studies (ASTM D
4546, 1996).
Chapter 7
135
In the free swell test, the specimen was firstly loaded with a seating pressure of
6.9 kPa (AS 1289.7.1.1-2003 recommends a seating load of 25kPa. However, as
suggested by Sridharan et al., 1986, 6.9 kPa seating pressure was used in the
present study) and then inundated with distilled water. Under this constant
pressure, the axial deformation was measured with a dial gauge of 0.002 mm
precision. Each test was continued for at least 15 days to establish the relationship
between the free swell and the elapsed time from the start of the inundation. The
swell was observed to be increasing even after two weeks as shown in Figures 7.2
to 7.4, hence hyperbolic curves were fitted to the test data as described in ensuing
section.
In the constant volume test (AS 1289.7.1.1 (2003)) not specifies this type of test
hence ASTM D 4546-96, Method C was followed) after placing the specimen in
the oedometer loading frame, water was supplied and the swelling was contained
by periodically increasing the load on the specimen with due care to avoid
compression of specimen. This test was continued until there was no further
volume change in the specimen in between two successive readings.
7.2.4 Results and discussion
7.2.4.1 Free swell
Figures 7.2, 7.3 and 7.4 show the relationships between free swell and elapsed
time for the three soils (SB16, SB24 and SB32), with and without EPS bead
inclusion. Free swell is the ratio of the amount of swell to the original thickness of
the specimen, expressed as percentage. It can be observed from the figures that the
magnitude of free swell is affected by the EPS content in the soil.
It can be observed from the Figures 7.2 to 7.4 that the magnitude of free swell
decreases as the EPS content increases from 0.0% to 0.9%. In absolute terms,
when compared with the free swell of control soil, the increase in EPS content
from 0.3% to 0.9% caused a reduction in free swell ranging 10 to 63% for SB16,
13 to 50% for SB24 and 13 to 48% for SB32 respectively. Furthermore, following
the commencement of the test, the magnitude of free swell was found to be
relatively low especially for higher EPS contents across all soil types.
Figure 8.7 Direct shear results for SB16 at 25 kPa normal stress, Figure 8.8 Direct shear results for SB16 at 50 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.
Figure 8.9 Direct shear results for SB16 at 100 kPa normal stress, Figure 8.10 Direct shear results for SB24 at 25 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.
Figure 8.11 Direct shear results for SB24 at 50 kPa normal stress, Figure 8.12 Direct shear results for SB24 at 100 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.
7 (b) 8 (b) Figure 8.13 Direct shear results for SB32 at 25 kPa normal stress, Figure 8.14 Direct shear results for SB32 at 50 kPa normal stress, (a) Shear stress vs. shear displacement and (a) Shear stress vs. shear displacement and (b) Vertical displacement vs. shear displacement. (b) Vertical displacement vs. shear displacement.
Figure 8.31 Stress-strain response of SB24 at different confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.
Chapter 8
208
SB32, 0.0% EPS
0
100
200
300
400
500
600
700
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25kPa 50 kPa100 kPa 200 kPaLine of peaks
SB32, 0.3% EPS
0
100
200
300
400
500
600
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25kPa 50 kPa100 kPa 200 kPaLine of peaks
(a) (b)
SB32, 0.6% EPS
0
100
200
300
400
500
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25kPa 50 kPa100 kPa 200 kPaLine of peaks
SB32, 0.9% EPS
0
50
100
150
200
250
300
350
0 5 10 15 20Axial strain, %
Dev
iato
r st
ress
, kP
a
25 kPa 50 kPa100 kPa 200 kPaLine of peaks
(c) (d) Figure 8.32 Stress-strain response of SB32 at different confining pressures for EPS contents of (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.
Chapter 8
209
Table 8.4 Deviator stress ( ) f31 σσ − and strain ( fε ) at failure for SB16
Figure 8.33 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB16.
SB24
25 kPa
50 kPa
100 kPa
200 kPa
0
50
100
150
200
250
300
350
400
450
500
0 0.2 0.4 0.6 0.8 1
EPS, %
Initi
al ta
ngen
t you
ngs
mod
ulus
, kP
a
Figure 8.34 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB24.
Chapter 8
211
SB32
200 kPa
25 kPa
50 kPa
100 kPa
0
50
100
150
200
250
300
350
0 0.2 0.4 0.6 0.8 1
EPS, %
Initi
al ta
ngen
t you
ngs
mo
dulu
s, k
Pa
Figure 8.35 Variation of Initial tangent Young’s modulus with confining pressure
and EPS content for SB32.
It can be observed from the Tables 8.4, 8.5 and 8.6 for SB16, SB24 and SB32
soils respectively, that for the same soil type with a specific EPS content,
increasing the confining stress results in an increase in peak deviator stress.
It is known that the initial tangent Young’s modulus increase with an increase in
confining pressure. The same trend was noticed in the present case for all SWEPS
specimens. However, this increase is more pronounced at 0.0% EPS content and
the difference in initial tangent Young’s modulus decreases with increasing EPS
content and confining pressure (Figures 8.33 to 8.35). This could be due to the
compression of EPS beads with increasing confining pressure.
Composite modulus was calculated based on the volume fraction of the EPS in
SWEPS mix from the equation of proportionality as per the following equations
Upper bound
EPSEPSSoilSoilc VEVEE += (8.1)
Lower bound
SoilEPSEPSsoil
EPSSoilc EVEV
EEE
+= (8.2)
Chapter 8
212
Where Ec is the initial tangent Young’s modulus of the composite, kPa
ESoil is the initial tangent Young’s modulus of soil, kPa
EEPS is the initial tangent Young’s modulus of EPS, kPa (in this case 6200
kPa)
VSoil is the volume fraction of soil in SWEPS mix,
VEPS is the volume fraction of EPS in SWEPS mix.
The resulting graph for SB16 at 25 kPa confining pressure is shown in Figure
8.36. However, it can be observed from Figures 8.33 to 8.35 that the experimental
values are lower than the lower bound values. It indicates that the composite
modulus based on the equation of proportionality is not suitable for the SWEPS
mixes. Each mix case has to be observed independently based on the mix design.
Figure 8.36 Calculated composite modulus for SB16 at 25 kPa confining pressure.
The composite modulus based on the Equations 8.1 and 8.2 are shown in Figures
8.37, 8.38 and 8.39 for SB16, SB24 and SB32 respectively.
Chapter 8
213
SB16, 25 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
SB16, 50 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
(a) (b)
SB16, 100 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa
Data points
SB16, 200 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa
Data points
(c) (d)
Figure 8.37 Calculated composite modulus for SB16 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
Chapter 8
214
SB24, 25 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
SB24, 50 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa
Data points
(a) (b)
SB24, 100 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa
Data points
SB24, 200 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
(c) (d)
Figure 8.38 Calculated composite modulus for SB24 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
Chapter 8
215
SB32, 25 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
SB32, 50 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
(a) (b)
SB32, 100 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
SB32, 200 kPa Upper bound
Lower bound
0
500
1000
1500
0 0.05 0.1 0.15 0.2 0.25Volume fraction of EPS
Mod
ulus
of
Ela
stic
ity, k
Pa Data points
(c) (d)
Figure 8.39 Calculated composite modulus for SB32 at confining pressures of (a) 25 kPa, (b) 50 kPa, (c) 100 kPa and (d) 200 kPa.
Chapter 8
216
8.2.2.1 Predictive model for initial tangent Young’s modulus
The multiple regression analysis of initial tangent Young’s modulus, EPS content
and soil type produced the following equation for the initial tangent Young’s
modulus.
3547.07.23621.015.171 σ+−+= EPSPIEti (8.3)
Where Eti is the initial tangent Young’s modulus in kPa,
PI is plasticity index of the soil in %,
EPS is EPS content in % and
3σ is the confining pressure in kPa.
Figure 8.40 The relation between measured and predicted initial tangent Young’s
modulus.
The Equation 8.3 is applicable for the range of soils tested in the present study. A
plot between the measured initial tangent Young’s modulus and the predicted
initial tangent Young’s modulus is shown in Figure 8.40.
8.2.3 Shear strength parameters
Peak major principal and minor principal stresses were used for the determination
of the total stress shear stress parameters from the UU triaxial tests. For each soil
type, an s-t plot (Whitlow, 2000) was used to determine the cohesion (c) and angle
of internal friction (φ), where
Chapter 8
217
( ) fs 3121 σσ += (8.4)
( ) ft 3121 σσ −= (8.5)
where 1σ = peak major principal stress, kPa
3σ = minor principal stress, kPa
At the point of failure, the Mohr circle touches the Mohr-Coulomb failure
envelope and thus alternative failure criteria is given by
αtansat += (8.6)
The parameters of this stress point failure criteria, a and α are related to those of
the Mohr-coulomb criteria as follows
αφ tansin = (8.7)
ac =αcos (8.8)
Figures 8.41 to 8.43 present the s-t plots for the UU tests showing the alternative
failure envelope. The variation of cohesion mobilized (cuu) and angle of internal
friction (φuu) with and without the addition of EPS beads for different soils is
shown in Figure 8.44. The subscript “uu” refers to the parameters derived from
UU test. Note that φuu > 0 as the test specimens were not saturated.
SB16
0.6% EPS0.9% EPS
0.0% EPS
0.3% EPS
0
100
200
300
400
500
600
0 100 200 300 400 500 600
s, kPa
t, kP
a
Figure 8.41 s-t plots for SB16.
Chapter 8
218
SB24
0.6% EPS0.9% EPS
0.0% EPS0.3% EPS
0
100
200
300
400
500
600
0 100 200 300 400 500 600
s, kPa
t, kP
a
Figure 8.42 s-t plots for SB24.
SB32
0.9% EPS
0.0% EPS
0.3% EPS0.6% EPS
0
100
200
300
400
500
600
0 100 200 300 400 500 600s, kPa
t, kP
a
Figure 8.43 s-t plots for SB32.
Chapter 8
219
(a)
(b)
(c)
Figure 8.44 Variation of cohesion (c) and angle of internal friction (φ) for different soils (a) SB16, (b) SB24 and (c) SB32.
Chapter 8
220
Figure 8.45 Typical failure modes of SWEPS mixes.
It can be observed from the Figure 8.44 that by increasing the EPS content, both
cohesion and angle of internal friction decrease for all SWEPS mixes. However,
the changes in c and φ for SB32 are relatively small, indicating that the effect of
EPS on the shear strength of highly plastic soil is not significant.
Typical failure modes of soils with and without EPS beads are shown in Figure
8.45. From the figure it can be observed that with increasing EPS content the
shape, inclination and roughness of the failure plane changes. Without EPS beads
the failure plane is fairly linear and short. However, with the addition of EPS
beads the failure plane increased in length. The inclination was observed to vary
from 62° to 56° for SB16, 60° to 57° for SB24 and 58° to 53° for SB32 from 0.0%
EPS to 0.9% EPS contents. The roughness of the failure plane increases with
increasing EPS content because the failure has to occur along the soil-EPS
interfaces.
Variation of cohesion and angle of internal friction for all SWEPS mixes at
different plasticity indices corresponding to the respective bentonite contents is
presented in Figures 8.46 and 8.47, respectively. It is known that cohesion
increases with increasing plasticity index and angle of internal friction decreases
with plasticity index. The similar trend was observed in the present study across
all EPS contents.
Chapter 8
221
0
10
20
30
40
50
60
70
80
90
100
15 20 25 30 35 40 45 50 55Plasticity Index, %
Coh
esio
n, k
Pa
0.0% EPS0.3% EPS0.6% EPS0.9% EPSRegression model
Figure 8.46 Variation of cohesion with EPS for different soils.
0
10
20
30
40
50
15 20 25 30 35 40 45 50 55
Plasticity Index, %
Ang
le o
f int
erna
l fric
tion,
o
0.0% Measured0.3% Measured0.6% Measured0.9% MeasuredRegression model
Figure 8.47 Variation of angle internal friction with EPS for different soils.
The nature of cohesion and angle of internal friction variations in SWEPS mixes
can be explained in the light of EPS characteristics. The tensile strength of EPS at
Chapter 8
222
a density of 20 kg/m3 is 200 kPa whereas compressive strength (based on 10%
strain criterion) is 100 kPa (Horvath, 1995). Furthermore, Zou (2001) observed
the angle of internal friction and cohesion for an EPS specimen of 20 kg/m3 under
UU test. The values were 8.6° and 42.6 kPa respectively. Therefore, it is not
surprising that this present study has found that as EPS replaces the soil fraction;
the cohesion decreases proportionally with %EPS because of the lower strength of
EPS beads when compared with the control soils. Since the EPS beads form weak
links within the soil matrix, failure has to occur either through compression,
slippage or tensile failure of the beads along the failure plane.
Similar behaviour was observed by Puppala et al. (2000) while carrying out
unconfined compressive strength (UCS) tests on specimens of expansive soils
reinforced with polypropylene fibres. It was observed that the use of a large
amount of fibres reduced the cohesive strength since the volume of soil was
decreased and the loss of cohesive strength was not compensated by the
polypropylene fibres reinforcement. Another reason was related to the lowering of
the compacted unit weight of the soils associated with the increase in fibre
dosages.
In a different study, while discussing the shear strength characteristics of clay-tyre
chip mixture, Edil (2004) mentioned that the strength of the clay was not
increased with the addition of tyre chips. He also stated that, in fact, adding tyre
chips resulted in a lower shear strength values at low normal stresses. It was
suggested that poor bonding between clay and tyre chips was the cause of the
problem. While the bond between the soil and EPS mixes in the present case may
have played a role, the compressibility of EPS beads has clearly reduced the shear
strength of the composite.
Minegashi et al. (2002) conducted a series of static loading UU triaxial
compression tests on a loam mixed with EPS beads and cement at confining
pressures of 50, 100, 150 and 200 kPa. They observed that the deviator stress or
the mobilised compressive strength increased with an increase in confining
pressure on, or after reaching an axial strain of about 5%. No noticeable peak
strengths were observed. They further observed that at confining pressures of
Chapter 8
223
more than 100 kPa, there was no distinct difference in the peak deviator strength
with the increase in beads content. Contrary to this observation, in the present
case there was a decrease in deviator strength with increasing EPS contents. This
could possibly be due to variation in soils moisture content, the type of EPS beads
used and EPS gradation.
In addition, as EPS beads are impermeable, excess pore water pressure may
develop more easily within the specimen. In a similar case, Ingold and Miller
(1983) mentioned that reinforcing clay specimens with continuous horizontal
layers of aluminium foil caused reductions in undrained compressive strength to
about 50%. Thus, in the present case, with increasing EPS contents there could be
a significant increase in pore water pressure in the SWEPS mix which eventually
leads to failure.
8.2.3.1 Predictive models for cohesion and angle of internal friction
The cohesion and angle of internal friction of SWEPS mixes was examined by
focussing on the influence of the soil type (PI of 22, 38 and 53%) and EPS content
(0.0, 0.3, 0.6 and 0.9%).
The experimental data was quantitatively analysed by multiple regression models
by correlating cohesion and angle of internal friction with PI and EPS. The
equation obtained from the multiple regression analysis is
EPSPIc 48.2694.045.32 −+= (8.9)
EPSPI 54.917.02.37 −−=φ (8.10)
Where c is cohesion, kPa,
φ is angle of internal friction, °
PI is plasticity index, %
EPS is quantity of EPS, %
These equations are valid only for the range of soils tested and for EPS contents
evaluated. The validity of this equation was checked and a comparison was made
between the measured and predicted values for the cohesion and angle of internal
Chapter 8
224
friction as shown in Figures 8.46 and 8.47. Figures 8.48 and 8.49 show the
experimentally obtained cohesion and angle of internal friction vs. the predicted
values respectively.
R 2 = 0.8852
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70 80 90
Measured cohesion, kPa
Pre
dict
ed c
ohes
ion,
kP
a
Figure 8.48 The relation between measured and predicted cohesion.
R 2 = 0.8188
0
5
10
15
20
25
30
35
40
0 10 20 30 40Measured angle of internal friction
Pre
dict
ed a
ngle
of i
nter
nal f
rict
ion
Figure 8.49 The relation between measured and predicted angle of internal friction.
8.2.4 Failure envelopes
Figure 8.50 shows the failure envelopes in principal stress space, namely the
variation of axial stress at failure �1f , with confining stress, �3, for SB16, SB24
and SB32 at different EPS contents.
Chapter 8
225
Generally, published results (Maher and Gray, 1990; Ranjan et al., 1996; Kaniraj
and Havanagi, 2001) showed that the addition of fibres resulted in a bilinear
failure envelope. This was attributed by Maher and Gray (1990) and Ranjan et al.
(1996) to the existence of a critical confining stress, critσ ; below and above which
there are two linear portions. They further noticed that the slope of the initial
linear portion is steeper than the second portion above the critσ . According to
Maher and Gray (1990), the initial linear portion was characterised by the pullout
failure of the fibres and the second linear portion was characterised by tensile
failure of the fibres.
In the present investigation, SWEPS mixes exhibited a single linear trend instead
of bilinear trend (Figure 8.43). Regression analysis of all the data points of each
envelope in the present case showed that for all the confining pressure ranges the
measured data points fitted well on a straight line which can be expressed as
1311 cmf += σσ (8.11)
where m1 and c1 are the slopes of the straight line and the intercept of the straight
line with the f1σ axis, respectively (Kaniraj and Gayathri, 2003). The results of
the regression analyses are presented in Table 8.7.
There are some reports in the literature where a linear relationship is observed.
For example, Foose et al. (1996) showed that failure envelopes for sand-tyre chip
mixtures are linear for loose sands and non-linear for dense sands. Similarly,
Tatlisoz et al. (1997) reported a linear failure envelope for the sandy silt-tyre chip
mixtures and non-linear envelope for sand-tyre chip mixtures. From these results
it may be inferred that fine grained soil composites tend to show a linear failure
envelope as what has been observed with the SWEPS composite of the current
study.
Andersland and Khattack (1979) performed tests on kaolinite clay reinforced with
cellulose pulp fibre. The shear strength under various testing conditions
(undrained, consolidated-drained and consolidated-undrained) increased with
increasing fibre content. The ductility of the specimen was also found to increase
Chapter 8
226
with increasing fibre content. The load transfer mechanism on the fibre soil
interface was explained as an attraction between soil particles and fibres.
SB160.3% EPS
0.6% EPS0.9% EPS
0.0% EPS
100
300
500
700
900
0 50 100 150 200 250Confining stress, kPa
Maj
or p
rinc
ipal
st
ress
, kP
a
(a)
SB240.3% EPS0.6% EPS0.9% EPS
0.0% EPS
100
300
500
700
900
0 50 100 150 200 250
Confining stress, kPa
Maj
or p
rinc
ipal
st
ress
, kP
a
(b)
SB32
0.6% EPS
0.9% EPS
0.0% EPS0.3% EPS
100
300
500
700
900
0 50 100 150 200 250Confining stress, kPa
Maj
or p
rinc
ipal
st
ress
, kP
a
(c)
Figure 8.50 Failure envelopes of (a) SB16, (b) SB24 and (c) SB32
at various EPS contents.
Chapter 8
227
Table 8.7 Regression coefficients from failure envelopes.
Soil EPS m1 c1 R2 value
SB16
0.0 3.600 177.82 0.999
0.3 3.008 161.02 0.993
0.6 2.564 129.61 0.992
0.9 2.277 108.84 0.987
SB24
0.0 3.102 257.13 0.998
0.3 2.721 211.52 0.999
0.6 2.639 152.18 0.992
0.9 2.508 107.21 0.998
SB32
0.0 2.608 262.24 0.999
0.3 2.539 239.14 0.995
0.6 2.323 198.11 0.996
0.9 1.802 173.77 0.986
Even though kaolinite was not used in the present case, the results showed that the
addition of EPS beads decreased the shear strength. However, ductility was
increased with the addition of EPS as was noticed with fibre added soils from the
previous study.
While stabilising expansive (black cotton) soils with fly ash mixes, Pandian et al.
(2001) have found that there was an optimum fly ash content, above which there
would be strength reduction with the addition of fly ash to the soil. In contrast, for
the present investigation, the optimum EPS content was not found because a
consistent decrease in the strength of the SWEPS mixes occurs with the addition
of EPS.
The shear strength of fibre-reinforced clay was more difficult to predict than that
of fibre-reinforced sand (Li, 2005). This was because of the difficulty in
quantifying the pore water pressure and consequently, the interface shear strength.
Chapter 8
228
Limited past research conducted on fibre-reinforced clay showed inconsistent
results regarding the shear strength increase due to fibre reinforcement (Li, 2005).
The fibre-clay interaction, investigated by Li (2005) using five fine grained soils
was found to be more complex than fibre-sand interaction. The shear strength was
found to be influenced by factors such as volume change, unit weight, compaction
water content, degree of saturation and strain levels. Even though these factors
were considered specifically in the present study, the above limitations could be
the reasons for the random variation of shear strength in the present results. For
example, unit weight, compaction water content and volume changes due to
compression of EPS beads might have influenced the shear strength results.
8.3 Effect of lime on the shear strength of SWEPS
As mentioned in Chapter 7, the effect of lime as a chemical stabiliser on the shear
strength of a SWEPS mix was investigated in addition to its effects on the
swelling characteristics. Due to the time constraint, only one reconstituted soil
was considered (SB24). The lime content was at optimum lime content and the
tests were conducted on the specimens after undergoing accelerated curing
conditions as described in Section 7.4. The variation of deviator stress with axial
strain and percentage of EPS for three different confining pressures is shown in
Figure 8.51. In addition, the variation of deviator stress with axial strain and
confining pressure for various EPS contents is shown in Figure 8.52.
The shear strength characteristics are similar to those of unstabilised SWEPS.
However, as expected, a significant increase in peak deviator stress was achieved
with the addition of lime as chemical stabiliser. In addition, it can also be
observed from the figures that by increasing the EPS contents the ductility of the
lime stabilised soils increased significantly. The lime stabilised soils took more
strain to reach failure with the EPS inclusion.
The s-t plots (Figure 8.53) were drawn for the lime stabilised SWEPS mixes.
Based on the y-intercept and slope of the modified failure shear envelopes, the
cohesion and angle of internal friction were calculated and compared with those
without lime in Figure 8.54 and 8.55, respectively.
Chapter 8
229
SB24, 50kPa, with lime
0
200
400
600
800
1000
1200
1400
0 2 4 6 8 10 12 14Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks
SB24, 100 kPa, with lime
0
300
600
900
1200
1500
1800
0 2 4 6 8 10 12 14Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks
(a) (b)
SB24, 200 kPa, with lime0
500
1000
1500
2000
2500
0 2 4 6 8 10 12 14Axial strain, %
Dev
iato
r st
ress
, kP
a
0.0% EPS 0.3% EPS0.6% EPS 0.9% EPSLine of peaks
(c)
Figure 8.51 Stress - strain curves at different EPS contents for lime-stabilised SB24 at confining pressures of (a) 50 kPa, (b) 100 kPa and (c) 200 kPa.
Chapter 8
230
SB24, 0.0% EPS, with lime
0
500
1000
1500
2000
2500
0 1 2 3 4 5Axial strain, %
Dev
iato
r st
ress
, kP
a
50 kPa100 kPa200 kPaLine of peaks
SB24, 0.3% EPS, with lime
0
200
400
600
800
1000
1200
1400
1600
0 1 2 3 4 5 6 7Axial strain, %
Dev
iato
r st
ress
, kP
a
50 kPa100 kPa200 kPaLine of peaks
(a) (b)
SB24, 0.6% EPS, with lime
0
200
400
600
800
1000
1200
0 2 4 6 8 10 12Axial strain, %
Dev
iato
r st
ress
, kP
a
50 kPa100 kPa200 kPaLine of peaks
SB24, 0.9% EPS, with lime
0
100
200
300
400
500
600
700
0 2 4 6 8 10 12 14Axial strain, %
Dev
iato
r st
ress
,kP
a
50 kPa100 kPa200 kPaLine of peaks
(c) (d)
Figure 8.52 Stress-strain response of lime-stabilised SB24 at different confining pressures with (a) 0.0% EPS, (b) 0.3% EPS, (c) 0.6% EPS and (d) 0.9% EPS.
Chapter 8
231
SB24 with lime
0.3% EPS
0.6% EPS
0.9% EPS
0.0% EPS
0
300
600
900
1200
1500
0 300 600 900 1200 1500
s, kPa
t, kP
a
Figure 8.53 s-t plots for SB24 with lime.
SB24
With lime
Without lime
0
50
100
150
200
250
0 0.2 0.4 0.6 0.8 1EPS, %
Coh
esio
n, C
uu, k
Pa
Figure 8.54 Variation of cohesion with and without lime for SB24.
Chapter 8
232
SB24
With lime
Without lime
0
5
10
15
20
25
30
35
40
45
50
0 0.2 0.4 0.6 0.8 1
EPS, %
Ang
le o
f int
erna
l fric
tion,
o
Figure 8.55 Variation of angle of internal friction with and without lime for SB24.
As expected, addition of lime has increased the cohesion in the soil due to
pozzolonic reactions for the same EPS content. Similar trend was also observed
with respect to angle of internal friction. However, with increased EPS content,
even though lime was added, the cohesion and friction angles were decreased. As
described earlier this can be attributed to the replacement of soil particles by the
EPS beads which eventually reduced the shear strength of the composite.
Consoli et al. (1998) reported that fibre reinforcement increased the peak and
residual shear strength of cement treated soils, and reduced the brittleness. In the
present case, EPS beads increased the ductility as exhibited by the line of peaks.
However, the strength was not improved.
8.4 Summary
An experimental study was carried out to investigate the influence of recycled
EPS beads on the shear behaviour of reconstituted expansive soils by using both
direct shear test and triaxial shear tests.
Chapter 8
233
Direct shear apparatus was used to determine the influence of recycled EPS beads
on the shear response of the reconstituted soils. Three soil types and four EPS
contents by dry mass of soil were investigated. It was noticed that EPS beads
increased the initial settlement of the specimen under normal load. Dilation was
observed in soil-EPS mixes at high normal loads.
The SWEPS mixes are composed of two contrasting materials in terms of their
particle size and strength. The reconstituted soil is a clayey sand with high
plasticity whereas recycled EPS beads are coarser but have a smaller internal
friction angle. By their nature EPS beads are compressible. Hence, by combining
these two materials a different composite is produced. In this case, the addition of
EPS beads does not contribute a strength increase as was provided by some
fibrous compounds in soils.
EPS is different from other materials such as fibres, tyre chips etc., in the sense
that the latter materials have reasonably high tensile strength and consequently
can take care of much of the tensile stresses in the soil. However, EPS has a low
tensile stress. Moreover, with its elasticity, EPS can easily deform under loads,
therefore, reducing the strength of the composite considerably.
When used in the context of expansive soils, strength is not the only criterion. In
addition to strength, swelling also is a predominant factor to be considered. It has
been demonstrated that the while strength is not increased, inclusion of EPS beads
can reduce shrinkage and swelling potential of soil.
The range of results produced shows the high dependency of the behaviour of the
SWEPS mixes on the EPS content at the soils’ optimum moisture content. Hence,
each situation needs to be considered separately to arrive at a SWEPS mix
suitable for the site and soil conditions.
Following this shear behaviour of SWEPS mixes, another very important aspects
of expansive soils, suction and desiccation, were briefly investigated with the
inclusion of EPS beads. This is described in Chapter 9.
Chapter 8
234
One particularly useful property of SWEPS is its relatively high ductility, which
suits certain earth structure applications. Compacted soil liners used in final cover
systems, for example, must be sufficiently ductile to accommodate differential
settlement and must be resistant to cracking caused by moisture variations e.g.
desiccation (Qian et al., 2002). Chapter 10 will discuss the application of SWEPS
technology in landfills.
235
CHAPTER 9 - SUCTION AND DESICCATION STUDIES Since soil is a very complex material, the inclusion of additive(s) can cause
substantial, and sometimes unpredictable, alterations of its properties. In the
foregoing chapters, the influence of recycled EPS beads on the swelling (Chapter
7) and the strength characteristics of the reconstituted expansive soils (Chapter 8)
were discussed. In this chapter, the influence of EPS on suction and desiccation is
described.
9.1 Suction studies
Suction controls different properties of unsaturated soils such as strength, stiffness
hydraulic conductivity and desiccation. In order to understand the behaviour of
partially saturated soils, the suction in the soil must be measured (Bulut et al.,
2000; Skinner, 2000). The section describes the limited study performed in order
to assess the influence of recycled EPS beads on the suction of the reconstituted
expansive soils.
In engineering practice, soil suction consists of two components viz., osmotic
suction and matric suction (Fredlund and Rahardjo, 1993). Osmotic suction is
caused by the chemical activity and mineralogy of the soil. Specifically, osmotic
potential arises from variations in the salt content in the pore fluid from one point
to another. In contrast to osmotic suction, matric suction is usually ascribed to
capillary forces, soil texture and the air-water interface that exist in an unsaturated
soil. It is therefore strongly related to geometrical factors such as pore size and
shape (Houston et al., 1994). Total suction is a function of both osmotic and
matric suction.
Ridley (1993) defined matric suction as a measure of the energy required to
remove a water molecule from the soil matrix without the water changing its state
and total suction was defined as a measure of the energy required to remove a
water molecule from a soil matrix through evaporation.
Chapter 9
236
There are many direct and indirect measurement techniques available to establish
matric and total suctions in soils. For matric suctions, the direct methods include
the instruments used actually to measure the pore water suction, as in the case of
suction plate, the pressure plate, the pressure membrane apparatus, tensiometers,
the osmotic tensiometer and the Imperial suction probe. On the other hand, the
indirect techniques measure the intermediate parameter that can be related to
suction through a separate calibration or theoretical support, as in the case of filter
paper (in contact), porous blocks and thermal conductivity sensors (Ridley, 1993;
Montanez, 2002).
The total suction can be determined by measuring relative humidity. Measurement
techniques suitable to determine the total suction are the transmitter psychrometer,
the thermocouple psychrometer and the non-contact filter paper method (Ridley,
1993).
More thorough discussions on the concept, measurement and use of the suction
components have been presented by Fredlund and Rahardjo (1993). Additional
discussions on the use of suction in expansive soils are also available from
Johnson and Snethen (1978) and Snethen and Huang (1992)
Bulut et al. (2000) studied the comparison of total suction values from
psychrometer and filter paper methods for three different soils compacted well
above the optimum moisture content. They observed that both methods were
sensitive to suction changes at high moisture contents. However, from the
standard deviation results they concluded that the filter paper method gave more
consistent results.
Suction testing using filter paper on a routine basis is relatively inexpensive
(approximately the same cost as for natural moisture content) and provides
additional means of laboratory quality control (Houston et al., 1994).
Furthermore, Thompson and McKeen (1995) observed that in normal commercial
laboratories where the work is usually performed by engineering technicians,
reliable and consistent test data are obtained using the filter paper method. A
Chapter 9
237
thorough discussion on the use and calibration of filter papers for suction
measurements was presented by Leong et al. (2002).
The basic principle in this method is that the moisture content of the filter paper
comes into equilibrium with that of the soil specimen either through vapour flow
or liquid flow. Here the filter paper may be regarded as a suction sensor. At
equilibrium, the filter paper is allowed to absorb water through vapour flow from
the atmosphere surrounding the soil specimen in a non-contact method to measure
the total suction. However, if the filter paper is allowed to absorb water through
fluid flow by capillary effect, as in a contact method, then matric suction is
measured (Bulut et al., 2000). At equilibrium, soil suction is equal to filter paper
suction.
Based on their test results, Sibley and Williams (1990) suggested that Whatman
No. 42 filter paper was the most appropriate for use over the entire range of
suction investigated (0 to 100 MPa). Furthermore, Leong et al. (2002) stated that
the performance of Whatman no.42 filter paper was more consistent than other
types of filter papers. This filter paper was also found to be more consistent in
quality and have less hysteresis.
In the current research, soil suction determinations were made on reconstituted
soils with and without EPS beads through an indirect means by using ash-free
quantitative type Whatman No. 42 filter papers from the same batch, since it is the
only known technique which covers the full range of suction measurement (from
zero to perhaps 100 MPa) (Houston et al., 1994). Whatman No.42 filter paper has
shown to be a suitable adsorbent although other grades and types of filter papers
are also used (Gourley and Schreiner, 1995). Both total and matric suction
measurements are possible with this method. The test procedure is simple,
straightforward and does not require any special equipment (Leong et al., 2002);
however, proper care must be exercised in measurement.
9.1.1 Filter paper calibration relationships
The calibration curves relating soil suction moisture content of filter papers have
been established using filter papers, salt solutions, pressure plates and membranes,
Chapter 9
238
and tensiometers (Bulut et al., 2000). The salt solutions are usually used for high
suction ranges and the pressures plates and tensiometer are used for low suction
ranges.
Several relationships between filter paper (absorbent material) moisture content
and suction have been established for various types of filter papers such as Fisher
quantitative filter papers, Schleicher and Schuell filter paper, and Whatman filter
papers (McQueen and Miller,1968; Al-Khafaf and Hanks, 1974; Hamblin, 1981;
Chandler et al., 1992; Houston et al., 1994 and Leong et al., 2002).
For the Whatman No. 42 filter paper a number of calibration curves are presented
in Table 9.1. Leong et al. (2002) attributed the differences in calibration equations
to several factors viz., quality of filter paper, suction source used in calibration,
hysteresis and equilibration times. Based on the use of soil sample of ‘known’
suctions for calibration purposes, they suggested a set of equations for Whatman
No. 42 filter paper for different moisture contents. These equations were selected
for the current study to determine the matric and total suctions.
Table 9.1 Calibration curves for Whatman No.42 filter papers (after Leong et al., 2002).
Figure 10.8 Variation of average annual percolation rate with EPS content.
Chapter 10
290
The variations in the present study may also be due to the limitations in HELP
model in considering the physical processes that control unsaturated water
movement such as matric potential in soil barrier layers (Dwyer, 2003).
According to Dwyer (2003) HELP consistently under predicts the surface runoff
using SCS runoff method. Further, this method does not take into account a
rainstorm’s intensity or duration. Hence, actual field testing by considering the all
parameters are needed in understanding the accrual outcome with the SWEPS
landfill cover materials.
10.4 Summary
The results of hydraulic conductivity, compressibility and water balance analysis
are presented for one of the reconstituted expansive soil (SB24) with 0.0%, 0.3%
and 0.6% EPS contents. The addition of recycled EPS beads increased the
hydraulic conductivity in the soil. It was observed that the hydraulic conductivity
of the SWEPS mixes increases slightly with 0.3% EPS when compared with the
control soil, but with 0.6% EPS a moderate increase (one order of magnitude) is
observed. As previously mentioned, it is generally accepted that hydraulic
conductivity for a landfill liner or cover materials should be around 10-9 m/s or
less. While the control soil and soil with 0.3% EPS content may satisfy this
criterion, soil with 0.6% EPS content may only be used as a cover material e.g.
evapotranspiration cover.
Similarly, on compressibility characteristics it is noted that EPS beads inclusion
can make a SWEPS mix compressible. Hence, the addition of EPS to a soil may
potentially result in greater consolidation settlement. However, being a
lightweight material, SWEPS mixes exert less overburden pressure on the
underlying soils consequently resulting in less settlement.
Water balance analysis was performed using Visual HELP software with
statistically significant weather data. It revealed that the leakage or percolation
increases with increasing EPS content in the barrier soil owing to the increased
hydraulic conductivity of the SWEPS mix. Even though addition of EPS for
landfill cover applications shows an advantage in terms of desiccation control, the
increase in leachate rate needs consideration for its application. It needs further
analysis from field studies.
291
CHAPTER 11 - CONCLUSIONS AND RECOMMENDATIONS
The principal endeavour of this research was to assess the feasibility of reusing
waste EPS beads in geotechnical applications. Assessing the suitability of
recycled EPS beads for mass applications is of paramount importance for the
efficient and cost effective recycling of these waste products. Efforts have been
made to recycle the waste EPS products in various ways. However, it is rather
ironic that some valuable attributes of EPS products are also impediments to their
widespread recycling.
The use of pre-puff EPS beads in geotechnical applications is being practiced in
Japan for applications involving dredged soils at high moisture contents. In the
current research, the use of recycled EPS beads for geotechnical applications, for
controlling swell-shrink of expansive soils in particular, has been investigated.
This last chapter of the thesis concerns with the scientific contributions of the
research, the applicability of SWEPS mixes in geotechnical engineering and the
mix design criteria followed by conclusions of the various investigative exercises
undertaken during the course of this research program. The possible topics for
further research are also discussed.
11.1 Scientific contribution from this research
The following significant achievements may be claimed for this study:
• This research contributed to the minimisation of waste reaching to the landfill
thus promoting the quality of environment. It also promotes the sustainability
in construction through the recycling and reuse of waste materials.
• This research fulfilled the aim of developing Soil with EPS (SWEPS) mixes
and demonstrating its effectiveness in controlling of swell-shrink potential of
expansive soils.
• It demonstrated that EPS inclusion is influenced by the moulding moisture
content of the soil, and for optimum strength it is necessary to mix and
compact EPS beads at optimum moisture content of the soil.
Chapter 11
292
• It identified that EPS inclusion reduces the shear strength of soils and hence,
there is a need to incorporate chemical admixers. The combined lime-EPS
stabilisation has been found to be very effective in controlling the expansive
soil behaviour.
• This research is a significant step forward in the development of SWEPS
mixes for their bulk utilisation in geotechnical applications. This research
opens up further avenues for reuse of EPS beads in construction activities.
• The data generated in this research can form a basis for further research and
improvements in the development of SWEPS mixes. Furthermore, a modified
flowchart for lime-EPS stabilisation is suggested for engineering applications.
11.2 Engineering applications of this technique It is well known that for compacted clayey soils, compaction conditions affect the
swelling, shrinkage and desiccation behaviour of the soil. To reduce the swelling,
compaction on wet side of optimum is recommended (Holtz and Kovacs, 1981).
However, this wet side compaction contributes to the shrinkage and desiccation.
Hence, to reduce the cracking potential, compaction on the dry side is preferred
(Daniel and Wu, 1993). Because of the changing weather patterns around the
world, both compaction cases can produce unfavourable behaviour. Hence, there
is need to find other suitable alternatives.
Use of recycled EPS beads has been found to be an alternative admixer in
expansive soils to control the swell-shrink potential. To optimise the strength, if
no chemical stabiliser is added, EPS beads should be added to the soil at optimum
moisture content until a uniform and consistent mix is achieved. The mixing can
be done on-site using a concrete mixer or through a mixing plant using a pug mill.
However, it was observed that plant mixing is more effective than on-site mixing
(Miki, 1996) Field compaction can be done in the usual way, no additional
equipment is needed. While the EPS beads are compressed during compaction,
they can still have an influence on swelling and shrinkage due to its elastic
properties as demonstrated in Figure 11.1 for recycled EPS beads. It can be
inferred from the figure that when the bead is compressed the air inside the bead
Chapter 11
293
is decreased in volume but increased in pressure to maintain load equilibrium.
When the load is removed, the air void expands.
Figure 11.1 Compression and elastic rebound of recycled EPS beads upon loading and
unloading respectively. The potential application of this SWEPS mix can include backfill behind a
retaining wall, fill at the shoulder of pavements, and fill below concrete slabs
when there is a possibility of differential settlements. This technique is especially
suitable if differential swelling and settlements are expected. This technique may
also be used in landfill cover systems.
11.2.1 Backfill behind a retaining wall
The significant advantage gained because of the addition of EPS to the soil is the
considerable reduction in the dry unit weight of the composite thus formed for the
same moisture content. Thus it is suitable as a lightweight backfill material.
Furthermore, this reduction is particularly important in retaining walls as the
composite can be expected to produce less lateral force on the retaining wall. This
will allow the retaining wall to be made thinner.
The low value of compacted dry unit weight of SWEPS mix can result in greatly
increased stability for embankments built on weak soils. While it may not be
Chapter 11
294
relevant for Australian climatic conditions, the use of recycled EPS beads may
also result in reduced frost penetration due to their favourable thermal
characteristics when compared to other soils.
11.2.2 Pavements and shoulders
In pavements, equilibrium conditions will eventually be reached under the
pavements with respect to moisture content. However, because of the exposure to
weather elements, the pavement shoulders experience differential swelling and
shrinkage which can be cyclic in nature. In this situation, if soil mixed with EPS
beads is used for the shoulder, the movements can be taken care of.
Similarly, applications under for paving slabs where extreme movements due to
moisture variation can happen, this technique can prove to be a good option.
In paving applications, precaution should be taken in placing the SWEPS mix.
This composite material should not be placed as a top layer by itself. There should
be a sufficient cover above the SWEPS mix to take care of any chemical spillages
and UV degradation.
11.3 SWEPS Mix design criteria
Soils from one place may differ in imperative aspects from the soils tested at other
locations, climatic conditions and soil type (Basha et al., 2005). The complexity in
soil conditions and the differences in soil properties make it necessary in each
case to resolve the problem by adopting some form of mix design instead of
adopting a generic approach. Because of the variabilities in the index properties of
different soils it was not possible to produce a stand-alone model or equation
which is applicable to all soil types across all EPS contents. Furthermore, it was
noticed in scoping studies (Chapter 5) that the addition of EPS beads depends on
the moulding moisture content of the soil. Hence, instead of a design formula, a
mix design procedure is provided for the application of this technique to a much
broader range of situations.
A mix design criteria modified from Thomspon (1970) is suggested. It is basically
used in the mix design of lime stabilised soils for pavements. The same was
modified by incorporating EPS content as another factor.
Chapter 11
295
Figure 11.2 Flow chart for the mix design of SWEPS mixes (modified after Thompson, 1970).
The primary objective of this mixture design is to identify an optimum EPS and
stabiliser content based on the strength criteria that is a function of the how the
Determine clay content
Determine optimum moisture content
Select binder type
Find optimum lime content
Select between 2 to 6%
Determine EPS content based on
homogeneous mixture at OMC
Fix EPS content and/or binder content
Determine density of the composite
Determine CBR and/or UCS
Find swelling and shrinkage
Accept binder content and EPS application rate
depending up on field application
Change binder content
Increase moisture
content until workability is
achieved
Strength Requirement
No Yes
Lime Cement
OK
Not OK
OK
Not OK
Chapter 11
296
composite will be used; as a backfill material, a compacted fill material or a
landfill cover material. Blending recycled EPS beads with chemical admixer can
produce even more significant effect while still providing a cost effective solution.
To optimise the density and strength with the addition of EPS beads and lime,
density tests, California Bearing Ratio (CBR) and Unconfined Compressive
Strength (UCS) tests can be performed. Figure 11.2 shows the mix design
approach, which depends on the strength criteria. The selection of the material
depends on the strength to be gained, which is a function of the optimum moisture
content and optimum lime content. The addition of EPS beads at optimum
moisture content needs to be considered prior to testing for the strength criteria.
11.4 Conclusions from this research
As an original research, this investigation was unavoidably exploratory in nature
and primarily conceived based on a hypothesis that recycled EPS beads can be
used for geotechnical applications as a swell-shrink modifier of expansive soils or
as a landfill cover material. More than just focussing on the modification of the
soil’s swell-shrink characteristics, the influence of recycled EPS beads on the
overall behaviour of the soil was also investigated by performing compaction,
strength, desiccation, hydraulic conductivity and compressibility tests.
This research is a step forward in the significant use of recycled EPS beads in
geotechnical applications. This research opens up other possible avenues for the
reuse of EPS in bulk quantities. The following conclusions can be drawn from this
study.
• The most advantageous properties of EPS (lightweight and non-
decomposable) create a major hindrance in recycling. Most of the EPS
recycling efforts have been focussed on mechanical, chemical and thermal
methods. However, the current system in practice for collection, sorting and
reclamation of EPS products are too costly, mainly because they are small in
scale and extremely labour intensive. Furthermore, these methods require
energy to a greater extent while the rate of recycling is low. Hence, in this
research, possible large scale recycling options for geotechnical applications
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such as swell-shrink modifier, desiccation crack controller were evaluated
using a dredged soil and reconstituted expansive soils by mixing EPS beads.
• This research evaluated the recyclability and miscibility factors that control
the mixing of EPS beads with soils through preliminary studies with a dredged
soil at optimum moisture content. Among other things, how the moulding
moisture content influences the addition of EPS beads was investigated. It was
observed that with higher moisture content, more EPS can be added into the
soil. For example, at 39% of moulding moisture content (which is optimum
moisture content for this soil) a maximum quantity of 1.25% of EPS can be
added. Whereas increasing the moulding moisture content to 50% resulted in
3% EPS content as the maximum possible quantity. In addition, the influence
of EPS on the unit weight and strength of the dredged soil was also
investigated. It was noticed that EPS inclusion reduces the unit weight but
decreases the strength of the soil. The results established the technical
feasibility and the potential beneficial use of recycled expanded polystyrene as
a soil modifier.
• In continuation, the influence of recycled EPS beads on the swell-shrink
properties of expansive soils was investigated through the use of artificially
reconstituted expansive soils made by mixing fine sand and sodium bentonite.
Three different soils notated as SB16, SB24 and SB32 representing 16%, 24%
and 32% of bentonite contents respectively were selected. These soils also
represent soils of low, medium and high plasticity indices. It was observed
that the use of recycled EPS beads as an admixer leads to the reduction in
magnitude of swelling and shrinkage of expansive soils. For example, in
absolute terms, when compared with the free swell of control soil, the increase
in EPS content from 0.3% to 0.9% caused a reduction in free swell form 10 to
63% for SB16, 13 to 50% for SB24 and 13 to 48% for SB32 soils
respectively. Furthermore, this research also demonstrated that the reduction
of swelling and shrinkage is primarily caused by replacement of soil particles
as well as the elasticity of the EPS beads.
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• The strength characteristics of the test soils with the addition of EPS beads
were studied using unconsolidated-undrained triaxial tests. It was observed
that strength reduces with the addition of recycled EPS beads because of the
compressible nature of EPS beads. Hence, for improving the strength of the
composite, chemical stabilisers are needed.
• Limited studies on suction, hydraulic conductivity, desiccation of the SWEPS
mixes were conducted to investigate their overall behaviour. Based on the
results, it can be concluded that suction and hydraulic conductivity increase
whereas desiccation decreases with the addition of EPS beads.
• Water balance analysis was performed using Visual HELP software with
statistically significant weather data. It revealed that the leakage or percolation
increases with increasing EPS content in the barrier soil owing to the
increased hydraulic conductivity of the SWEPS mix. Even though addition of
EPS for landfill cover applications shows an advantage in terms of desiccation
control, the increase in leachate rate needs consideration for its application. It
needs further analysis from field studies
11.5 Recommendations for further studies
Considering that this research is the first in the use of EPS to control swell-shrink
potential of expansive soils, there is ample scope for further investigations or
development. Based on the results of the present investigation, the following
recommendations are made for further research and advancement in the use of
recycled EPS beads in geotechnical applications.
• In the present investigation the recycled EPS beads selected were in the range
of 3 to 9 mm in size. Hence, the effect of EPS gradation variation on the
swell-shrink behaviour of expansive soils should be investigated in the future.
• There is research going on in many parts of the world to study the use
industrial by-products such as fly ash, slag etc. for their bulk utilisation in
geotechnical applications. Research can therefore be conducted by mixing
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recycled EPS beads with those industrial by-products to enhance or
compliment their behaviour for their mass use in geotechnical applications.
• Influence of virgin EPS beads on the swelling properties of expansive soils
can also be investigated in lieu of recycled EPS beads. The recycled EPS
beads are irregular shape whereas virgin beads are circular in shape.
Consequently, it is important to compare the performance of these two types
of beads.
• The influence of sand fraction and recycled EPS beads on the swell-shrink
behaviour of expansive soils can also be evaluated.
• Large scale field investigation can be conducted to test for an effective field-
scale mixing techniques and also to observe the behaviour of SWEPS mixes
for desiccation control of landfill cover systems.
• At this juncture it is important to note that although limited small-scale
experimental investigations can provide useful observations in comparative
analysis for the variabilities observed; these smaller scales did not replicate
the heterogeneities that can dominate performance such as the case in natural
expansive soils or actual landfill covers. Hence, SWEPS mix technique needs
to be tested on pilot scale before embarking on further applications.
• Even though the use of EPS as geofoam blocks in geotechnical engineering
spanning over 20 years shows its durability, the long term behaviour as
affected by chemical and other environmental factors have not been fully
investigated in this study. These issues should be investigated in the future.
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301
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Matlab program Matlab® image processing program used for extracting the Crack Intensity Factor (CIF)in desiccation studies. Function Image_Processing(picture_no) % Reading Input File tue = num2str(picture_no) tue1 = '.jpg' tue2 = [ tur tue1 ]; f = imread(tue2); imshow(f); I = rgb2gray(f); % Converts to Black and White Image threshold = graythresh(I); bw = im2bw(I,threshold); imshow(bw) % Detects Centre of the Image bw = bwareaopen(bw,30); se = strel('disk',2); bw = imclose(bw,se); bw = imfill(bw,'holes'); imshow(bw) c = [43 185 212]; r = [38 68 181]; BW2 = bwselect(bw,c,r,4); imview(bw), imview(BW2) % Counts Number of Pixel outside of the Central Image tec = 0; for i = 1:480 for j = 1:640 if (BW2(i,j)==0) tec = tec + 1; end; end; end; tec BW2 = ~BW2; imshow(BW2) % Superimposing of the images to Eliminate Unwanted Portions of the Image figi=imoverlay(f,BW2,[1 1 1]); imshow(figi) figi1 = im2bw(figi); imshow(figi1) tec1 = 0; for i = 1:480
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for j = 1:640 if (figi1(i,j)==0) tec1 = tec1 + 1; end; end; end; % Calculates the Percentage of Crack Area crc = 0; crc = ((tec1)/((640*480)-tec))*100; 342 341 341