ABSTRACT
Constitutive modelling of unsaturated soils has progressively incorporated a number of features that are deemed to be necessary to achieve a satisfactory reproduction of their mechanical behaviour. Among them, the following can be mentioned: a central role of matric suction in the description of behaviour, the use of more then one stress variable in the formulation, the recognition that collapse behaviour (i.e. the compression of the soil upon wetting) is irreversible and the increase of shear strength with suction. Another important characteristic is the requirement that a model for unsaturated soils should be compatible with existing models for saturated materials.
