Abstract:A model that reproduces the coupled deformation and two-phase flow(with special interest to gas migration) through a waste containment engineered barrier system has been developed. The simulation presented in this paper is novel because variable permeability interfaces that depend on deformation are introduced to model the contacts between backfill materials and solid rock or concrete structures. Calculated results of pressures,stresses and volumetric water contents are compared with measurements showing an encouraging agreement which permits to conclude that the model is quite accurate in representing the actual processes that take place in a large-scale in-situ test.