An anisotropic elasto-plastic model for unsaturated soils

A new anisotropic elasto-plastic constitutive model for unsaturated soils (ABBM) has been developed, by combining features of the conventional Barcelona Basic Model (BBM) for unsaturated soils and the anisotropic S-CLAY1 model for saturated soils. In addition, the possibility of a non-linear variation of cohesion intercept with suction is introduced for both the BBM and the ABBM. Simulations with the ABBM and the BBM have been compared with experimental data from tests on compacted Jossigny silt reported by Cui & Delage (1996). The ABBM is able to provide a much better match than the BBM to the observed shape and size of the yield surface produced by one-dimensional compaction. In addition, the ABBM is able to provide improved predictions of yield stresses and volumetric strains during constant suction shearing, particularly if a non-linear variation of cohesion intercept with suction is incorporated. The current version of the ABBM can, however, sometimes result in unrealistic predictions of immediate post-yield softening, and further work is required to refine and fully validate the model.