Abstract: This paper presents a numerical model for the finite element analysis of transient deformation and seepage problems in unsaturated soils. A definition of the generalized effective stress for unsaturated soils is proposed on the basis of the two stress variable formula. The Alonso constitutive model to simulate the nonlinear mechanical behavior of unsaturated soils is integrated into the model. With introduction of the natural coordinates in the stress space a consistent algorithm for the non smooth multi surface pressure dependent plasticity is derived.