A numerical simulation of the hydro-mechanical behaviour of an unsaturated porous medium is presented. The coupled hydro-mechanical model used is based on the continuum theory of mixtures and treats the unsaturated soil as a three phase porous medium (solid, liquid and gas). Principal variables are the solid deformation, the liquid pressure and the gas pressure. The two fluid phases are in motion and a non-linear pore pressure - saturation relation is used. The resulting system of equations is discretized in space using the finite element technique and in time by the - method. The comparison of numerical results and experimental test data shows that this hydro-mechanical model is capable to reproduce the principal phenomenon in the case of a hydric solicitation. The three phase formulation is compared to a simplified version considering only a two phase medium with static air phase. Merits and shortcomings of the two approaches are shown.