khalid ibrahim ahmed

302 Pages·2014·4.5 MB·English

by  Khalid Ibrahim Ahmed

EFFECT OF GYPSUM ON THE HYDRO-MECHANICAL
CHARACTERISTICS OF PARTIALLY SATURATED
SANDY SOIL

KHALID IBRAHIM AHMED

Geoenvironmental Research Centre
Cardiff School of Engineering
Cardiff University

Thesis submitted in candidature for the degree of Doctor of Philosophy
at
Cardiff University
September 2013
DECLARATION
This work has not been submitted in substance for any other degree or award at this
or any other university or place of learning, nor is being submitted concurrently in
candidature for any degree or other award.
Signed ………………………. (Khalid Ibrahim Ahmed)
Date …… 04 / 09/2013

STATEMENT 1
This thesis is being submitted in partial fulfilment of the requirements for the degree
of Doctor of Philosophy (PhD).
Signed ………………………. (Khalid Ibrahim Ahmed)
Date …… 04 / 09/2013

STATEMENT 2
This thesis is the result of my own independent work/investigation, except where
otherwise stated. Other sources are acknowledged by explicit references. The views
expressed are my own.
Signed ………………………. (Khalid Ibrahim Ahmed)
Date …… 04 / 09/2013

STATEMENT 3
I hereby give consent for my thesis, if accepted, to be available for photocopying and
for inter-library and for the title and summary to be made available to outside
organisations.
Signed ………………………. (Khalid Ibrahim Ahmed)
Date …… 04 / 09/2013

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ABSTRACT
Gypsum rich soils are of wide occurrence in the Middle East. They cover large
areas of Iraq. Gypsum is one of the moderately soluble salts that can have significant
effect on the engineering properties of soils. The effect of gypsum content and the
stress state on the main hydraulic functions, volume change, shear strength and
deformation characteristics of unsaturated silty clayey sand were experimentally
examined. Statically compacted specimens of synthetic sand-gypsum mixtures were
used. A new stress controllable pressure plate device was developed. The modified
device was used to establish simultaneously both the stress-dependent soil-water
characteristic curves (SD-SWCCs) and the stress-dependent hydraulic conductivity
functions (SD-HCFs) during drying and wetting paths.
The test results revealed that the parameters of the drying SWCC such as the
water holding capacity, the air-entry suction, the air-entry water content, and the
residual suction are clearly increased with increasing gypsum content. Same effect of
gypsum was noticed on the wetting SWCC parameters. A clear decrease in saturated
water content, desorption rate, absorption rate, and water holding capacity with
increasing the applied net normal stress was noticed. Transient outflow methods
were used to measure the SD-HCFs. An increase in the SD-HCFs with increasing
gypsum content was found. Clear hysteresis effects on k(ψ) and minor hysteresis on
k(w) were noticed. It was found that the outflow methods can be applicable between
the air-entry suction and residual suction only.
Direct shear tests were carried out on saturated and unsaturated specimens. The
unsaturated specimens were air-dried and tested under constant water content
conditions. Matric suction values were evaluated by incorporating the SD-SWCC test
results. The friction angle related to matric suction (b), the effective stress parameter
(χ), and the suction stress ( ′) were found clearly decrease with increasing gypsum
s
content and with increasing the net normal stress level. However, test results of
saturated specimens revealed that the effective shear strength parameters (′, c′) are
noticeably increased with increasing gypsum content in the soil mixture.

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ACKNOWLEDGMENTS

In the Name of Allah, the All- Merciful, the All-Compassionate.
The praise is due to Allah, the All-Powerful, the All-Knowing, the All-Wise and the
Compassionate for giving me the strength, health, patience and perseverance to
complete this work in its best.
I would like to express my sincere gratitude to my senior supervisor Prof. Hywel
Thomas and the co-supervisors Dr. Snehasis Tripathy and Dr. Talib Mahdi for all
continuous support, motivation and invaluable academic guidance. Special thanks are
extended to the examination panel, Prof. Chris Clayton, Prof. David Barrow, and Dr.
Steve Rees for their worth comments, guidance and careful review of this thesis.
I would like to especially thank the Embassy of the Republic of Iraq / Cultural
attaché for financial support during my study. My gratitude is also extended to all
Professors of the University of Baghdad / College of Engineering for teaching me the
principles of engineering through (1978-1986).
Great thanks also to the Geotechnical technician Mr. Len Czekaj and all the technical
staff in Cardiff School of Engineering for their assistance in the lab. My special
thanks also extended to all academic staff especially Dr. Michael Harbottle for his
annual reviews of my research. I would like to express my gratitude also to all admin
staff in the research office and the Geoenvironmental research centre especially Mrs
Pauline Welsh, Mrs Chris Lee, Mrs Jeanette Whyte, Mrs Aderyn Reid. My sincere
thanks also extended to my colleagues and friends in the Geoenvironmental Research
Centre and other School Departments for their friendship and kindness.
Finally, and most of all, I would like to express my deepest gratitude and
appreciation to my wife and my children Dhuha, Ibrahim and Ahmed for their help,
sacrifices, and patience during my studies.
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TABLE OF CONTENTS
DECLARATION ii
ABSTRACT iii
ACKNOWLEDGMENTS iv
TABLE OF CONTENTS v
LIST OF TABLES xi
LIST OF FIGURES xiii
1: INTRODUCTION 1
1.1. General background 1
1.2. Objectives and scope of the research 4
1.3. Thesis organization 7
2: LITERATURE REVIEW 9
2.1. Introduction 9
2.2. Gypsiferous soils 10
2.2.1. Gypsum properties 11
2.2.2. Effect of gypsum on soil behaviour 13
2.2.3. Effect of soaking on mechanical properties of gypsiferous soils 15
2.3. Unsaturated soil state 16
2.3.1. State variables and material variables 16
2.3.2. Stress state variables 17
2.3.2.1. The variable effective stress state single approach 18
2.3.2.2. The two independent stress state variable approach 19
2.3.2.3. The true effective stress state variable approach 20
2.3.3. Total head as a state variable 22
2.4. Soil suction and soil-water characteristic curve 23
2.4.1. Soil suction and potential energy 23
2.4.2. Components of soil suction 25
2.4.3. Overview of soil suction measurement techniques 26
2.4.4. Chilled mirror hygrometer 28
2.4.5. Suction controlling techniques 29
2.4.6. Axis translation techniques 31
2.4.6.1. Pressure plate extractor 32
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2.4.6.2. Tempe pressure cells 34
2.4.6.3. Volumetric pressure plate extractor 36
2.4.6.4. Stress-controllable volumetric pressure plate 38
2.4.7. Soil-water characteristic curve 41
2.4.8. Hysteresis of soil-water characteristic curve 44
2.4.9. Influence of stress state on SWCCs 47
2.4.10. Influence of compaction water content on soil structure 50
2.5. Unsaturated hydraulic conductivity 51
2.5.1. Basic definitions 51
2.5.2. Overview of measuring methods of unsaturated conductivity 51
2.5.3. One-dimensional transient flow governing equation 53
2.5.4. Outflow methods 54
2.5.4.1. The multistep method 55
2.5.4.2. The one-step method 56
2.5.5. Ceramic disc impedance 58
2.6. Shear strength and failure criteria 59
2.6.1. The extended Mohr-Coulomb criterion 60
2.6.2. Single stress state Mohr-Coulomb criterion 62
2.6.3. True effective stress failure criterion 64
2.6.4. Shear strength prediction using constitutive models 66
3: MATERIALS, EQUIPMENT AND METHODOLOGY 68
3.1. Introduction 68
3.2. Materials and samples preparation 69
3.3. Soil classification parameters 70
3.4. Experimental programme 73
3.4.1. Compaction tests 73
3.4.2. Consolidation tests 74
3.4.3. Soil-water characteristic tests 76
3.4.3.1. Testing device 77
3.4.3.2. Specimen preparation 77
3.4.3.3. Testing procedure and calculations 78
3.4.4. Chilled mirror hygrometer tests 81
3.4.4.1. Testing device 81
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3.4.4.2. Specimen preparation and testing procedure 82
3.4.4.3. Representation of test results 83
3.4.5. Soil shrinkage characteristic tests 83
3.4.5.1. Testing procedure for SCCs 84
3.4.5.2. Calculations of CLOD tests 86
3.4.5.3. Mathematical modelling of SCCs 87
3.4.6. Stress-dependent soil-water characteristic tests 88
3.4.7. Stress dependent-unsaturated hydraulic conductivity function tests 89
3.4.8. Direct shear tests on saturated specimens 90
3.4.8.1. Overview 90
3.4.8.2. Direct shear testing device 91
3.4.8.3. Device calibration 92
3.4.8.4. Specimens preparation 94
3.4.8.5. Testing procedure and calculations 95
3.4.8.6. Stresses and strains 96
3.4.9. Direct shear tests on unsaturated specimens 98
3.4.9.1. Overview 98
3.4.9.2. Experimental programme 99
3.4.9.3. Specimens preparation 101
3.4.9.4. Device adjustment 102
3.4.9.5. Testing procedure for unsaturated soil specimens 105
3.4.9.6. Calculations of unsaturated shear strength functions 106
4: MODIFIED DEVICE FOR MEASURING TWO STRESS DEPENDENT-
UNSATURATED HYDRAULIC FUNCTIONS 109
4.1. Introduction 109
4.2. The modified stress controllable pressure plate device 110
4.2.1. Background 110
4.2.2. Uses and features of the modified device 110
4.2.3. Design and construction details 111
4.2.3.1. The base plate of the cell 113
4.2.3.2. The cell ring 114
4.2.3.3. The dual grooved spacers 115
4.2.3.4. The pneumatic compartment cap 117
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4.2.3.5. The cell assemblage 118
4.2.3.6. The pressurized air panel 118
4.2.4. Specimen preparation and testing procedures 120
4.2.4.1. Specimen compaction and saturation 120
4.2.4.2. Testing procedure for SD-SWCCs determination 121
4.2.4.3. Testing procedure for SD-HCF determination 122
4.2.4.4. Diffused air removal 123
4.3. Testing programme 124
4.3.1. SD-SWCCs tests 125
4.3.2. SD-HCFs tests 126
4.4. Calculations 126
4.4.1. Calculations of SD-SWCCs 126
4.4.2. Calculations of SD-HCFs 128
4.5. Summary 132
5: RESULTS AND DISCUSSION OF BASIC TESTS 134
5.1. Introduction 134
5.2. Effect of gypsum content on compaction characteristics 134
5.3. Effect of gypsum content on compressibility characteristics 139
5.4. Soil-water characteristics 143
5.4.1. Same specimen approach-SWCC tests 144
5.4.2. Separate specimens approach-SWCC tests 145
5.4.3. Effect of gypsum content on SWCC parameters 146
5.4.4. Matric suction-volumetric water content relationships 148
5.4.5. Applied suction and volume change 149
5.5. Water content-total suction relationships 152
5.6. Shrinkage characteristics 155
5.7. Concluding remarks 158
6: STRESS-DEPENDENT SOIL-WATER CHARACTERISTICS 160
6.1. Introduction 160
6.2. Test results preview 161
6.3. Effects of gypsum content on the SD-SWCCs parameters 169
6.3.1. Effects of gypsum content on SD-SWCCs-water content parameters 169
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6.3.2. Effects of gypsum content on the SD-SWCCs-suction parameters 170
6.3.3. Effects of gypsum content on the slope of the SD-SWCC 171
6.3.4. Effects of gypsum content on hysteresis phenomenon 172
6.3.5. Effect of gypsum content on suction-water content equalization time 173
6.4. Effects of net normal stress on SD-SWCCs parameters 174
6.4.1. Effect of net normal stress on initial water content of SD-SWCC 174
6.4.2. Effect of net normal stress on characteristic zones of SD-SWCC 175
6.4.3. Effects of net normal stress on SD-SWCCs characteristic points 176
6.4.4. Effect of net normal stress on the slope of SD-SWCCs 176
6.4.5. Effect of net normal stress on hysteresis phenomenon 176
6.5. Mathematical modelling of SD-SWCCs 177
6.6. Comparison of SWCCs obtained from different equipment 180
6.7. Combined SWCCs of different sand-gypsum mixtures 184
6.8. Summary and concluding remarks 188
7: STRESS DEPENDENT-UNSATURATED HYRAULIC CONDUCTIVITY
FUNCTIONS 189
7.1. Introduction 189
7.2. Effect of gypsum content on SD-HCFs 189
7.2.1. Hydraulic conductivity-matric suction relationships 190
7.2.2. Hydraulic conductivity-gravimetric water content relationships 196
7.3. Comparison of Doering's approach with Gardner's approach 201
7.4. Effect of net normal stress on SD-HCFs 204
7.4.1. Hydraulic conductivity-matric suction relationships 204
7.4.2. Hydraulic conductivity-gravimetric water content relationships 208
7.5. Summary and concluding remarks 211
8: SHEAR STRENGHTH AND DEFORMATION CHARACTERISTICS 213
8.1. Introduction 213
8.2. Results of direct shear tests on saturated specimens 213
8.2.1. Stress-strain characteristics 214
8.2.2. Effect of gypsum content on saturated shear strength 220
8.2.3. Mohr-Coulomb failure envelopes and shear strength parameters 221
8.3. Results of direct shear tests on unsaturated specimens 223
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8.3.1. Shear strength-water content relationships 224
8.3.2. Failure envelopes in plane of net normal stress-shear stress 226
8.3.3. Apparent cohesion and friction angle versus water content 230
8.3.4. Failure envelopes in plane of matric suction-shear stress 231
8.3.5. Effect of gypsum content on and χ 236
8.3.6. Prediction of unsaturated failure envelopes 239
8.3.7. Suction stress characteristic curves 242
8.3.8. Shear strength failure envelopes in terms of intergranular effective stress 247
8.4. Concluding remarks 249
9: CONCLUSIONS AND RECOMMENDATIONS 251
9.1. Conclusions from conventional, standard tests 252
9.2. Conclusions from developed-stress dependent-hydraulic tests 254
9.3. Conclusions from shear strength tests 257
9.4. Recommendations for future works 259
REFERENCES 262
APPENDIX: A 278
APPENDIX: B 279

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