Modelling Transition Between Fully and Partially Saturated Porous Media via a New Implicit Formulation of Interface Evolution

Air and water flows occurring in a porous material modify its mechanical properties. Evolution of the interface between saturated and partially saturated layers of a soil is of concern in this paper. In particular, the description of a drainage/imbibition front is developed gathering the two classical saturated and partially saturated poromechanical problems, with pressures of both fluids and solid displacement as unknowns. The presented model enables saturated and partially saturated layers to coexist without considering gaseous air dissolving into liquid water. Nucleation or collapse of the drainage/imbibition front moving from or reaching an air connected boundary is characterised considering the Signorini contact conditions on the liquid phase. The model abilities are confirmed numerically, via finite element simulations, showing among other that this new description of interface motion does not imply hysteresis phenomena. Parametric investigation developed with respect to drainage kinetics and thickness of the layer which regularises the interface between the saturated and the partially saturated domain are also provided.