Adaptation of existing behaviour models to unsaturated states : Application to CJS model

This paper proposes a general formulation of an elastoplastic model adapted to unsaturated soils. This formulation enters within the framework of two independent state variables descriptions. The choice of a particular effective stress combined with suction is made. The definition of this effective stress is based on the formulation of an equivalent pore pressure which is an essential point of this type of models. It will be discussed in this paper. This general formulation can be seen as a methodology allowing to adapt in a straightforward way most of elastoplastic behaviour models classically used in saturated soils mechanics to unsaturated states. It is shown that this synthesis can include most of recent models developed within the same framework. The last part of this paper is devoted to the adaptation of an existing complex elastoplastic model (CJS model) to unsaturated states using the methodology previously exposed. The model thus obtained is validated on various loading paths including œdometric, isotropic or triaxial compressions and also wetting tests simulating collapse phenomenon. This model extension shows the easiness introduced by the proposed methodology to adapt a given elastoplastic model to unsaturated states. Its validation illustrates by the way the abilities of the extended model to reproduce complex volumetric responses of an unsaturated soil.