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 the general laws of thermodynamics that provide broad principles to which all material behaviour adheres. The theoretical analyses are based on sound thermodynamic principles and provide a rigorous methodology, justified by comparison with soil test data, by which to predict and investigate the mechanical behaviour of unsaturated soils.
- provides engineers with a deeper appreciation of key characteristics of unsaturated soils
- covers a rapidly advancing area of study, research and engineering practice
- provides students and researchers a framework for understanding soil behaviour
- shows how to interpret experimental data on strength and compression
- the limited number of books on the subject are all out of date