Numerical modelling of unsaturated flow in multilayer soil covers

When dealing with the closure of waste disposal sites, multilayer soil cover systems with various type of soils are often use to secure the area and to control fluid motion. The hydraulic conditions in the cover, which usually involve different grain size materials and unsaturated flows are quite difficult to evaluate because of the non-linearity of the constitutive laws involved. This paper presents the results of a numerical study of unsaturated flow conditions in systems that comprise 2 (silt over sand) and 3 (sand -silt -sand) distinct layers and a simulation of the flow conditions using a commercially available finite-element code (SEEP/W). Five and two different cases were modelled with the 2 and 3 layers systems, respectively. The results demonstrate the importance of using materials with very different hydraulic properties. The laboratory and field works are briefly described. (J.S.). 51 refs., 12 figs., 1 tab