Constitutive Laws
Constitutive laws for unsaturated soils under nonisothermal conditions are presented in this Chapter. The development of the models is carried out in a progressive manner. First the Cam-clay constitutive law for saturated soils is briefly described. Using
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CONSTITUTIVE LA WS
A. Gens Technical University of Catalunya, Barcelona, Spain
ABSTRACT
Constitutive laws for unsaturated soils under nonisothermal conditions are presented in this Chapter. The development of the models is carried out in a progressive manner. First the Cam-clay constitutive law for saturated soils is briefly described. Using net stress and suction as independent stress variables, the Cam-clay model is generalized to include the effect of partial saturation. Some consequences of the model are reviewed and its prediction capabilities are tested in relation to some selected experimental results. Finally, the model is extended to include temperature effects. A suite of constiturive laws is therefore obtained capable of reproducing increasingly complex features of soil behaviour. Important advantages ensue from the fact that they can be regarded as progressive developments within a shared strain-hardening elasto-plastic framework.
A. Gens et al. (eds.), Modern Issues in Non-Saturated Soils © Springer-Verlag Wien 1995
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A. Gens
2.1. INTRODUCTION Modelling geotechnical problems involving thermo-hydro-mechanical coupled phenomena affecting partially saturated soils requires the development of appropriate constitutive laws that take into account the different aspects of behaviour and their interactions. The experimental evidence is still not sufficient to per mit the development of a comprehensive constitutive law which can be quantitatively validated in its entirety. It is probably more rewarding at this stage to try to establish a basic framework of behaviour which can accommodate different levels of complexity, from basic saturated soil behaviour to behaviour that includes the effects of unsaturation and temperature changes. In this way it will be possible to use in each case the simplest model compatible with the problem under exarnination. Moreover the relationship between the most complex framework and simpler weil known behaviour models will be more easily established. In this respect the framework provided by hardening plasticity should be potentially useful, especially the concepts of a yield surface as a locus of points where irreversible deformations take place and of the motion of this locus as a direct consequence of the occurrence of irrecoverable strains. These have been key in understanding saturated soil behaviour. Since saturated soil must be considered as a 'boundary condition' for the behaviour of partially saturated soils, it is very attractive to incorporate the effects of unsaturation and temperature into a framework that has proved successful in the simpler case of saturated soil under isothermal conditions. To do this, the Cam-clay models, the simplest members of the farnily of Critical State formulations, has been selected. It is recognized that it does not provide on accurate description of the detailed features of real soil behaviour although it is able to reproduce qualitatively a good number of the main characteristics of the mechanical behaviour of soils. If a more c
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