An elastoplastic model for unsaturated soils

A number of elastoplastic models have been proposed for unsaturated soils over the past three decades. These models have generally taken the form of simple extensions of elastoplastic models previously proposed for saturated soils. Laboratory testing programs have given rise to several unanswered questions regarding the acceptability of these models for unsaturated soils. There are questions related to: 1.) the variation of the yield stress with soil suction, 2.) the modeling of soils prepared from slurry conditions, and 3.) the existence of a smooth transition between saturated and unsaturated soil conditions. The model proposed in this paper addresses each of these questions by re-formulating the elastoplastic model for unsaturated soils through use of independent stress state variables. The re-formulation provides a smooth transition between the elastoplastic model for saturated and unsaturated soil conditions.