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

•The influence of effective stress and suction on bifurcation in partially saturated soils is accounted for in a new thermodynamics-based model.•The cross-coupling terms in the tangent stiffness allow the model to capture the coupled effects of suction and effective stress on the on the onset and inclination of the shear bands.•The model parameters are determined considering the experimentally observed bifurcation characteristics.•The interdependence of all internal variables, and the use of a single yield surface in stress-suction space facilitate the bifurcation analysis for the onset and orientation of localisation bands in various loading and hydraulic states.•The model is sensitive to conditions that favour bifurcation under the effect of hydro-mechanical coupling and dilation.