Unsaturated Soils. A fundamental interpretation of soil behaviour

  • ID: 2177176
  • Book
  • 304 Pages
  • John Wiley and Sons Ltd
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An understanding of the mechanical properties of unsaturated soils is crucial for geotechnical engineers worldwide, as well as to those concerned with the interaction of structures with the ground. This book deals principally with fine–grained clays and silts, or soils containing coarser sand and gravel particles but with a significant percentage of fines.

The study of unsaturated soil is a practical subject, linking fundamental science to nature. Soils in general are inherently variable and their behaviour is not easy to analyse or predict, and unsaturated soils raise the complexity to a higher level. Even amongst practicing engineers, there is often lack of awareness of the intricacies of the subject. This book offers a perspective of unsaturated soils based on recent research and demonstrates how this dovetails with the general discipline of soil mechanics.

Following an introduction to the basic soil variables, the phases, the phase interactions and the relevance of soil structure, an up–to–date review of laboratory testing techniques is presented. This includes suction measurement and control techniques in triaxial cell testing. This is followed by an introduction to stress state variables, critical state and theoretical models in unsaturated soils. 

A detailed description of the thermodynamic principles as applied to multi–phase materials under equilibrium conditions follows. These principles are then used to explore and develop a fundamental theoretical basis for analysing unsaturated soils. Soil structure is broken down into its component parts to develop equations describing the dual stress regime. The critical state strength and compression characteristics of unsaturated soils are examined and it is shown how the behaviour may be viewed as a three–dimensional model in dimensionless stress–volume space. The analysis is then extended to the work input into unsaturated soils and the development of conjugate stress, volumetric and strain–increment variables. These are used to examine the micromechanical behaviour of kaolin specimens subjected to triaxial shear strength tests and lead to observations not detectable by other means.

Unsaturated Soils: a fundamental interpretation of soil behaviour covers a rapidly advancing area of study, research and engineering practice and offers a deeper appreciation of the key characteristics of unsaturated soil. It provides students and researchers with a framework for understanding soil behaviour and demonstrates how to interpret experimental strength and compression data.

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Preface viii

Acknowledgements x

Introduction xi

Symbols xiii

1 Properties of Unsaturated Soils 1

1.1 Nature and genesis of unsaturated soils 1

1.2 Soil variables 3

1.3 Particle properties 7

1.4 Phase properties and interactions 9

1.5 Soil structure 22

1.6 Experimental techniques for examining pore size distribution 23

1.7 Pore size distribution 25

1.8 Conclusions 32

2 Suction Measurement and Control 34

2.1 Introduction 34

2.2 Techniques for measurement of suction 35

2.3 Control of suction in laboratory tests 52

2.4 Conclusions 56

3 Laboratory Techniques 57

3.1 Introduction 57

3.2 Material selection and specimen preparation 58

3.3 Experimental techniques for volume change and strength measurements 64

3.4 Essential measurements 69

3.5 Further details of triaxial and stress path testing techniques 71

3.6 Conclusions 85

4 Background to the Stresses, Strains, Strength, Volume Change and Modelling of Unsaturated Soil 87

4.1 Introduction 87

4.2 Stresses in soils 88

4.3 Strains in soils 90

4.4 Constitutive modelling 92

4.5 Critical state framework for saturated soils 98

4.6 The constitutive Barcelona Basic Model for unsaturated soils 107

4.7 Extended constitutive and elasto–plastic critical state frameworks for unsaturated soils 112

4.8 Concluding remarks 123

5 Thermodynamics of Soil Systems 127

5.1 Introduction 127

5.2 Outline of thermodynamic principles and systems 128

5.3 Introduction to equilibrium and meta–stable equilibrium 129

5.4 Variables of state 130

5.5 Extensive and intensive variables 131

5.6 The laws of thermodynamics 131

5.7 Thermodynamic potentials 135

5.8 Thermodynamic potentials in practice 138

5.9 Conjugate thermodynamic pairings 142

5.10 Influence of a gravitational field 144

5.11 Concluding remarks 145

6 Equilibrium Analysis and Assumptions in Triaxial Testing 147

6.1 Introduction 147

6.2 The minimum principles for the potentials 147

6.3 Isotropic loading conditions 149

6.4 Anisotropic loading conditions 152

6.5 Work input and the thermodynamic potential 155

6.6 The thermodynamic potential and axis translation 156

6.7 The thermodynamic potential and an aggregated soil structure 157

6.8 Conclusions 158

7 Enthalpy and Equilibrium Stress Conditions in Unsaturated Soils 160

7.1 Introduction 160

7.2 Role of enthalpy 160

7.3 Enthalpy and Terzaghi s effective stress for saturated soils 162

7.4 Enthalpy of unsaturated soils 163

7.5 The significance of 167

7.6 Stress state in unsaturated soils 171

7.7 Alternative equilibrium analysis 172

7.8 Graphical representation of stress state in unsaturated soils 173

7.9 Stress state variables and conjugate volumetric variables 174

7.10 Hysteresis, collapse and discontinuities in soil behaviour 176

7.11 Conclusions 179

8 Shear Strength and Compression Characteristics of Unsaturated Soils 180

8.1 Introduction 180

8.2 Shear strength and critical state characteristics of unsaturated soils 181

8.3 Equivalent strength parameters 200

8.4 Compression and critical state characteristics of unsaturated kaolin 200

8.5 Modelling of unsaturated kaolin 206

8.6 Structure, variables and parameters 208

8.7 Conclusions 210

9 Work Input, Conjugate Variables and Load–Deformation Behaviour of Unsaturated Soils 213

9.1 Introduction 213

9.2 Work input under triaxial stress conditions 213

9.3 Components of the deviator stress 218

9.4 Work input to unsaturated soils 218

9.5 Analysis of the mobilised stress ratios 220

9.6 Continuity relationships between strain–increments 221

9.7 Stress state variables and conjugate volumetric and strain–increment variables 223

9.8 The meaning and interpretation of stresses and strains 224

9.9 Analysis of triaxial experimental data on kaolin 232

9.10 Conclusions 251

References 254

Index 273

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E. J. Murray
V. Sivakumar
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