Wetting induced instabilities in layered slopes: A Material Point Method analysis

The increase of pore water pressure due to rainfall infiltration or upstream recharge is among the primary triggers of landslides, and soil layering has a significant effect on the hydromechanical behavior of the slope. The failure and post-failure behavior of heterogeneous layered slopes triggered by these phenomena are investigated in this study. In particular, a low permeability layer is embedded in a reference slope with different inclinations, and the impact of different saturation mechanisms on the post-failure behavior is assessed. To this aim, an unsaturated formulation of the Material Point Method (MPM) is used to reproduce the whole deformation process of a layered slope. The results show different failure and post-failure mechanisms and kinematics for both upstream recharge and rainfall infiltration (i.e., bottom-up and top-down saturation processes, respectively). Bottom-up saturation mechanism triggers deep failure mechanisms that barely evolve during the instability process. On the contrary, top-down saturation mechanism induces an anticipated shallow semi-planar failure limited by the location of the low permeable layer. These failures are characterized by high velocities and by a deepening of the slip surface during the post-failure process. Final displacements in both wetting mechanisms are of the same order of magnitude. The subsequent reactivation movements are observed as a result of the continuous injection of water in the system.