The present paper deals with the development and validation of an elasto-plastic material model for partially saturated soils.
A cap model originally proposed by DiMaggio and Sandler [
] for drained conditions, allowing control of dilatancy by means of a strain hardening cap, which intersects a shear failure surface in a non-smooth fashion, serves as starting point for the development of a constitutive model for partially saturated soils. In contrast to constitutive models for fully saturated soils, which are usually formulated in terms of a single effective stress variable, some of the most fundamental features of partially saturated soils can only be taken into account using two stress state variables. In the present case the material model is formulated in terms of the average soil skeleton stress tensor and matric suction, which is consistent with thermodynamic considerations.
Accounting for the evolution of both, the shear failure surface and the hardening law of the cap in terms of matric suction as well as including the third invariant of the deviatoric stress tensor in the formulation of the yield surfaces allows to predict the behavior of partially saturated soils. The capability of the developed model is demonstrated by the numerical simulation of a series of suction controlled tests, published in [
] and [
], involving hydrostatic compression, consisting of loading and unloading at several constant values of matric suction, triaxial compression tests, conventional triaxial compression tests, triaxial extension tests and simple shear tests at different values of matric suction and different values of hydrostatic net stress, i.e. total stress in excess of pore air pressure.