Deformation Mechanism of an Intermittent Rainfall-Induced Gently Dipping Accumulation Landslide

Numerous slope failures have been observed in deep-cutting gorges in Southwest China triggered by rainfall events. In this study, model-based experiments were conducted to investigate the failure mechanism of a gently dipping accumulation slope subjected to intermittent rainfall. The physical model was constructed using soil samples prepared according to similarity theory and direct shear test data. Intermittent rainfall conditions were simulated through controlled surface runoff and basal water pressure applied at the slope’s base. Throughout the experiment, deformation, earth pressure, and pore pressure were monitored using an array of transducers.

The findings indicate that slope failure initiated at the toe region. This was followed by staged sliding that progressively extended the unstable zone toward the trailing edge. Continued rainwater infiltration led to increased pore pressure, reduced matric suction, and decreased effective stress along the bedrock interface, ultimately contributing to slope failure.

A numerical simulation was also conducted under various intermittent rainfall scenarios. The results reveal that intermittent rainfall significantly affects slope stability even during non-rainy seasons, with slope stability weakening notably after rainfall cessation. Under equivalent total rainfall during the rainy season, longer intermittent periods correlate with greater slope instability. The first rainfall event after a prolonged dry interval markedly reduces slope strength.

Rainwater tends to accumulate along the gently sloping bedrock surface, forming transient groundwater levels and influencing the slope’s seepage field. The infiltration process primarily weakens soil strength parameters, while seepage thrust within the saturated zone exerts minimal influence on the slope’s safety factor. As groundwater levels rise, the sensitivity of the safety factor to rainfall gradually diminishes. Rainfall accumulation on gentle slopes leads to localized regions of high pore water pressure, enhancing the slope’s water retention capacity. Moreover, the stability coefficient of gently dipping landslides exhibits minor fluctuations under intermittent rainfall, rendering them prone to creep-slip deformation.