ABSTRACT
ABSTRACT: The main patterns of unsaturated fine soils are first described on the basis of literature results and tests carried out on a remoulded silt. After a short introduction on existing elastoplastic models dedicated to unsaturated soils, a new model, 8,,msat is proposed. This model makes use of two independent stress variables: the "saturated effective stress" a-uv, and the suction s. Si _unsa, is an improvement and extension of an existing model originally developed for saturated soils (HISS-81). It is able to reproduce the principal features of unsaturated soils: (a) existence on a drying path of a saturated domain with non-zero suction where plastic (irrecoverable) strains appear, (b) elastic behaviour on a drying path when the suction is greater than the air entry value, (c) wetting-induced collapse, (d) influence of mechanical stress state on the hydric behaviour, (e) increase of preconsolidation pressure with suction, (f) evolution of ultimate strength with suction. An extension to undrained conditions is also presented. The coupled hydro-mechanical formulation is deduced from the application of the theory of continuum mechanics to porous media. Finally, the model is modified in the framework of the disturbed state concept (DSC). This extension of Si_unsa, permits the prediction of the important softening behaviour commonly observed for unsaturated soils under deviatoric loading.
