Constitutive model for unsaturated soils: Validation on a silty material

A unified approach to model the behaviour of saturated and unsaturated soils has already been developed and an elastoplastic model initially developed for saturated soils has been extended to the case of unsaturated soils (Modaressi et al. 1994). The effective stress in unsaturated soils is defined using the capillary pressure. As a first approximation, this pressure is supposed to be not only a function of the pore pressure but also of the void ratio and the size of grains. Introducing a hardening parameter which depends on this capillary pressure, the elastoplastic model is generalized to unsaturated materials. The model is able to reproduce the most important features of the behaviour of unsaturated soils such as the collapse phenomenon on a wetting path. The model being validated qualitatively, it is applied to the Jossigny loam and the results are compared to experimental data.