Unification of plastic compression in a coupled mechanical and water retention model for unsaturated soils

In 2003, Wheeler, Sharma, and Buisson presented an elastoplastic constitutive model for unsaturated soils that represents both the mechanical behaviour and water retention behaviour, including the coupling between them. A crucial feature of the model is that the occurrence of plastic compression during all types of stress path is unified as a single process, with plastic compression during loading, plastic compression during wetting (collapse compression), and plastic compression during drying (irreversible shrinkage) all represented by yielding on a single loading-collapse yield curve. This paper explains how the model is able to predict the possible occurrence of plastic compression during each type of stress path and, in each case, links this to a physical explanation of the process involved. A simulation of an experimental test demonstrates the capability of the model to accurately predict the variation of both the void ratio and degree of saturation during successive stages of drying, loading, and wetting, where large magnitudes of compression occurred in all three test stages.