SMP-based representation of a constitutive model for unsaturated soils

The constitutive models for unsaturated soils are usually developed within the framework of the modified Cam-clay model, and with the generalized von Mises criterion, they are used to describe the constitutive behaviors of the unsaturated soils at general stress states. In using the generalized von Mises criterion, the yield surface is assumed to be a cycle in the plane. This assumption overestimates the strength of soils except that under the triaxial compression condition, yielding an incorrect estimation for the ratio of intermediate principal stress. The spatially mobilized plane (SMP) criterion takes into account the effect of the third stress invariant, and the shape of the resulted yield surface is a curved triangle in the plane, so that the resulted constitutive model is capable of describing very well the yielding and failure of soils. In this paper, a newly developed constitutive model for unsaturated soils, which is developed in the triaxial stress state, is generalized to the general stress space based on the SMP criterion. Comparisons between the model simulations and experimental results show that the new model can describe very well the behaviors of unsaturated soils without introducing any new parameters.