Modele de comportement a l'etat limite des sols satures et non satures

An elasto-plastic model describing the behaviour at yielding, which would apply to saturated and unsaturated soils is developed. First, a bibliographic synthesis of unsaturated soils behaviour is presented. It consists in describing water in unsaturated soils, in particular the phenomenon of suction and the water retention curve, and to present and discuss the most important existing models of yielding for unsaturated soils. In a second part an experimental programme was performed on reconstituted clay from Sainte-Rosalie both in saturated and unsaturated conditions. This programme consisted in: a set of compression tests performed under isotropic and anisotropic one-dimensional conditions, at different values of suction; a set of shearing tests at different values of confining stress and of matric suction. A set of tests for the determination of the water retention curve has also been performed on the Sainte-Rosalie clay at different void ratios. From the experimental results obtained on the Sainte-Rosalie clay and some from the literature, a new model based on the Leroueil and Barbosa (2000) model is proposed. This model, called GFY-2, takes in account the effect of anisotropy and kinematic hardening in addition to the non saturation. It assumes that the soil remains saturated until the air entry value is exceeded and its behaviour is then controlled by effective stresses. Beyond this particular point, the soil becomes unsaturated and the model then makes use of two independent stress variables: "modified net stress" sigma* = (sigma - ua) + chi* (ua - uw) and matric suction. The model represents, in a consistent and unified manner, most of the fundamental features of the behaviour of partially saturated soils which had been considered separately in previously proposed models. It also considers that the behaviour in compression is linked to the shear strength behaviour and both of them depend of water retention curve. The GFY-2 model presents most compression and shearing features of the behaviour at yielding of saturated and unsaturated soils. After that a subroutine has been developed in order to solve the constitutive equations of GFY-2 model. The application of this model to a virtual soil as well as to Sainte-Rosalie clay confirms the possibilities for the model to reproduce the most important features of saturated and partially saturated soil behaviour.