Simulation of subsurface flows associated with rainfall-induced shallow slope failures

Modeling transient subsurface flow along the soil-bedrock interface and the subsequent mounding of porewater pressure head in the slope toe zone is key to a successful prediction of rainfall-induced shallow slope failure and debris flow initiation. To this end, finite element analyses are performed on some model slopes subjected to artificial rainfall using calibrated soil-water characteristic curves (SWCCs) and soil permeability functions (SPFs). Analytical results highlighted the importance of lateral subsurface flow in modeling rainfall-induced shallow slope failure, which cannot be adequately simulated using one-dimensional seepage models. Analytical results also revealed that the formation of a saturated zone and an outward subsurface flow over the entire length of the soil-bedrock interface signals rapid slope mass wasting. Results of a comparative study showed that an accurate modeling of time-dependent subsurface water table development requires modifications to the analytical boundary conditions induced by the wash-away of the slope toe. An accurate physical model of shallow slope failures requires further works to address this issue.