Unsaturated Soils A fundamental interpretation of soil behaviour

by Murray, E. J.; Sivakumar, V.

• ISBN13: 9781444332124
• ISBN10: 1444332120
• Edition: 1st
• Format: Paperback
• Copyright: 2010-08-23
• Publisher: Wiley-Blackwell

Summary

This book examines the mechanical properties of unsaturated soils. It provides students and researchers in geotechnical engineering with a framework for understanding soil behaviour at a fundamental level and a model for interpreting experimental data. It also offers practitioners a deeper appreciation of the important characteristics of unsaturated soils. Chapter 1 provides a basic introduction to soil variables, the phases, the phase interactions and the relevance of soil structure to subsequent discussions. Particular reference is made to Mercury Intrusion Porosimetry (MIP) testing in describing the aggregated, bi-modal structure of unsaturated soils.An up-to-date review of laboratory testing techniques is presented in Chapters 2 and 3 including suction measurement and control techniques in laboratory triaxial cell testing. The basis of the testing is important if the ideas subsequently developed are to be properly applied. Chapter 4 introduces the stress state variables, critical state and theoretical models in unsaturated soils. This review of current ideas provides a background to subsequent analyses, which differ principally in the description of unsaturated soils as controlled by a dual stress regime with the relative volumes of the phases playing an essential role in defining the volumes through which the stresses act.Chapters 5 and 6 dive into a detailed description of thermodynamic principles as applied to multi-phase materials under equilibrium conditions. In particular, the significance of the thermodynamic potentials, including enthalpy, is described. It is shown that it is possible to deal with anisotropic stress conditions as the thermodynamic potentials are extensive variables. The significance of the minimisation of the thermodynamic potentials at equilibrium and the meanings of equilibrium and meta-stable equilibrium are outlined.Chapters 7 and 8 use the thermodynamic principles established earlier to develop an alternative theoretical basis for analysing unsaturated soils. Soil structure is broken down into its component parts to develop an equation(s) 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 extended in Chapter 9 to the work input into unsaturated soils and the development of conjugate stress, volumetric and strain-increment variables. These are used to examine experimental triaxial shear strength data on kaolin. The formulation for energy dispersion allows not only the anisotropic stress-strain behaviour on a macromechnical level to be appraised, but also the stress-strain behaviour of the aggregated packets of soil particles and water on a micromechanical level to be examined. Analysis of the experimental data highlights phenomena that cannot be explained by other means.Unsaturated Soils draws on analogous behaviour in physics and chemistry to explain important phenomena and the authors have kept the theoretical part of the book interesting but thorough. The behaviour of soils is influenced by many factors but is compliant with

Author Biography

Edward J. Murray is Director of Murray Rix Geotechnical, UK

Vinayagamoothy Sivakumar is Senior Lecturer at Queen's University Belfast, UK

Table of Contents

Preface	p. viii
Acknowledgments	p. x
Introduction	p. xi
Symbols	p. xiii
Properties of Unsaturated Soils	p. 1
Nature and genesis of unsaturated soils	p. 1
Soil variables	p. 3
Particle properties	p. 7
Phase properties and interactions	p. 9
Soil structure	p. 22
Experimental techniques for examining pore size distribution	p. 23
Pore size distribution	p. 25
Conclusions	p. 32
Suction Measurement and Control	p. 34
Introduction	p. 34
Techniques for measurement of suction	p. 35
Control of suction in laboratory tests	p. 52
Conclusions	p. 56
Laboratory Techniques	p. 57
Introduction	p. 57
Material selection and specimen preparation	p. 58
Experimental techniques for volume change and strength measurements	p. 64
Essential measurements	p. 69
Further details of triaxial and stress path testing techniques	p. 71
Conclusions	p. 85
Background to the Stresses, Strains, Strength, Volume Change and Modelling of Unsaturated Soil	p. 87
Introduction	p. 87
Stresses in soils	p. 88
Strains in soils	p. 90
Constitutive modelling	p. 92
Critical state framework for saturated soils	p. 98
The constitutive Barcelona Basic Model for unsaturated soils	p. 107
Extended constitutive and elasto-plastic critical state frameworks for unsaturated soils	p. 112
Concluding remarks	p. 123
Thermodynamics of Soil Systems	p. 127
Introduction	p. 127
Outline of thermodynamic principles and systems	p. 128
Introduction to equilibrium and meta-stable equilibrium	p. 129
Variables of state	p. 130
Extensive and intensive variables	p. 131
The laws of thermodynamics	p. 131
Thermodynamic potentials	p. 135
Thermodynamic potentials in practice	p. 138
Conjugate thermodynamic pairings	p. 142
Influence of a gravitational field	p. 144
Concluding remarks	p. 145
Equilibrium Analysis and Assumptions in Triaxial Testing	p. 147
Introduction	p. 147
The minimum principles for the potentials	p. 147
Isotropic loading conditions	p. 149
Anisotropic loading conditions	p. 152
Work input and the thermodynamic potential	p. 155
The thermodynamic potential and axis translation	p. 156
The thermodynamic potential and an aggregated soil structure	p. 157
Conclusions	p. 158
Enthalpy and Equilibrium Stress Conditions in Unsaturated Soils	p. 160
Introduction	p. 160
Role of enthalpy	p. 160
Enthalpy and Terzaghi's effective stress for saturated soils	p. 162
Enthalpy of unsaturated soils	p. 163
The significance of ¿	p. 167
Stress state in unsaturated soils	p. 171
Alternative equilibrium analysis	p. 172
Graphical representation of stress state in unsaturated soils	p. 173
Stress state variables and conjugate volumetric variables	p. 174
Hysteresis, collapse and discontinuities in soil behaviour	p. 176
Conclusions	p. 179
Shear Strength and Compression Characteristics of Unsaturated Soils	p. 180
Introduction	p. 180
Shear strength and critical state characteristics of unsaturated soils	p. 181
Equivalent strength parameters	p. 200
Compression and critical state characteristics of unsaturated kaolin	p. 200
Modelling of unsaturated kaolin	p. 206
Structure, variables and parameters	p. 208
Conclusions	p. 210
Work Input, Conjugate Variables and Load-Deformation Behaviour of Unsaturated Soils	p. 213
Introduction	p. 213
Work input under triaxial stress conditions	p. 213
Components of the deviator stress	p. 218
Work input to unsaturated soils	p. 218
Analysis of the mobilised stress ratios	p. 220
Continuity relationship between strain-increments	p. 221
Stress state variables and conjugate volumetric and strain-increment variables	p. 223
The meaning and interpretation of stresses and strains	p. 224
Analysis of triaxial experimental data on kaolin	p. 232
Conclusions	p. 251
References	p. 254
Index	p. 273
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