Suction Stress–Based Rainfall Intensity–Duration Method for Slope Instability Prediction

A method directly using rainfall records to predict a slope’s potential instability is devised. The method consists of three sequential steps: identifying the critical suction stress (pore water pressure when soil is saturated) profile of a given slope, developing a rainfall intensity–duration threshold curve for the slope, and using rainfall record to determine if the threshold is reached (failure occurs) or not (no failure). It innovatively uses a slope’s strength parameters and slope angle to develop the critical suction stress (tensile) or compressive pore water pressure profile where, at each depth within the slope, the effective stress reaches the failure state. Hydromechanical numerical modeling is then conducted under various rainfall intensities to identify their corresponding duration for slope failure, thus, the rainfall intensity–duration threshold curve of the slope. Two previously well-documented and studied rainfall-induced slope instability cases; one near the town of Edmonds, Washington State, and the other near the village of Rüdlingen in northern Switzerland are used to validate the method. Excellent predictions of the slope failure depth and timing are demonstrated, indicating the effectiveness of the proposed method. Because the suction stress–based rainfall intensity–duration curve is characteristic of a given slope and it can be determined a priori, the method provides a practical way to conduct real-time rainfall monitoring and predict instability for a specific slope, and a pathway to forecast instability of natural slopes in a region.