Rainfall-induced Slope Failure Patterns Controlled by Seepage Processes: Insights from Flume Experiments

The hydrological evolution within slopes is the root cause of rainfall-triggered landslides. Natural slope heterogeneity in soil and structure leads to variable hydrological behavior and complex failure patterns, while relevant control mechanisms are not fully clarified. This study employed flume experiments on rainfall-induced landslides to monitor the wetting and failure processes of three model slopes with distinct soil and structural characteristics. Results indicate that, compared to single-layer slope, the two-layer slopes experienced a transition from vertical infiltration to lateral flow and developed a perched water table at the soil interface. The presence of fractures alters the shape of the wetting front while influencing local moisture response rates. After shallow sliding occurred, two-layer slopes transition to deep shear failure, shifting the failure patterns compared to single-layer slopes. Surface fractures define failure boundaries. The altered seepage patterns and formation of a perched water table under soil heterogeneity provide the stress and hydrodynamic conditions enabling the transition to deep-seated cross-layer sliding. Preferential flow in cracks creates local high water heads in the perched water layer, enabling fractures to govern failure scale. This study reveals that seepage changes in heterogeneous soils dominate slope failure, offering important insights for landslide hydrological modeling and accurate stability analysis.