The effect of hydro-mechanical coupling on the onset and orientation of localisation bands in partially saturated soils

Constant suction triaxial tests on partially saturated soils demonstrate the dependence of the onset and orientation of localisation bands upon different mechanical loading and saturation conditions, in addition to the material properties of soils. This effect of hydro-mechanical coupling, via the combination of effective stress and suction, on the onset and inclination of the shear bands is investigated in this paper using a model with a single yield surface dependent on both stress and suction. The cross-coupling terms in the asymmetric tangent stiffness allow the model to capture the coupled effects of suction and effective stress on the behaviour upon yielding and hence facilitate the bifurcation analysis for the onset and orientation of localisation bands in various loading and hydraulic states. The model parameters are determined with its experimental bifurcation characteristics, showing the sensitiveness of conditions that favour bifurcation under the effect of hydro-mechanical coupling and dilation.