A HYDRO-MECHANICAL MODEL FOR PREDICTING INFILTRATION-INDUCED LANDSLIDES

Infiltration induced landslides are common in hillslope environments and are one of the most deadly and costly natural hazards in these areas. Therefore, development of a tool to account for both hydrological and mechanical processes in hillslopes leading to landsliding is critical for the accurate prediction and study of such hazards. We describe a two-dimensional coupled hydro-mechanical numerical model that implements a rigorous, yet simple framework for simulating stress, deformation, and variably-saturated flow. The model simulates the effects of slope morphology, transient hydrology, and stress-strain deformation on stability by computing the distribution of effective stress and implements a new definition of the factor of safety calculated at each point. The factor of safety is based on the potential stress path of the first invariant of the stress tensor that occurs at each point under an infiltration loading condition. Finite element methods are used to couple the governing equations for variably saturated flow with classical linear elasticity equations for analyzing the hydrologic and mechanical behavior of the slope. The state of effective stress at each point is calculated by accounting for its two components, total stress and suction stress. Slope geometry, boundary conditions, and hydrologic initial conditions are specified by the user. Results from a case study of a steep coastal bluff in the Seattle, WA area are presented. Contour maps with the distribution of principle effective stresses, angle of potential failure, and the factor of safety are comparable with field observations. This model provides a comprehensive tool for understanding and predicting the physical processes driving the onset of infiltration-induced mass movement in hillslope environments.