Equivalent stress approach in creation of elastoplastic constitutive models for unsaturated soils

This paper introduces an equivalent stress for elastoplastic modeling of unsaturated soils. This equivalent stress unifies various models for unsaturated soils with regard to the stress variables used and allows for a simple separation of the saturated and unsaturated phases of behavior. Moreover, the equivalent stress computed for a given model for unsaturated soil can be used in an existing model for saturated soil so it will gain the ability to model the former. The unsaturated plastic volumetric behavior of the new model is inherited mostly from the parent model for unsaturated soil. The behavior upon shearing depends on both models: the shape of the yield locus is inherited from the original model and the increase of the elastic zone (and possible shift of the elastic zone) from unsaturation depends on the model for the unsaturated soil from which the equivalent stress was taken.