Objective During the 2024 flood season, Zigui County in Hubei Province experienced multiple episodes of intense rainfall, resulting in 111 significant geological hazard incidents. Among them, the Wanshuitian landslide on July 17 was particularly severe. Rainfall monitoring data showed that the slope was subject to two consecutive heavy rainfall events separated by only 4 days —an exceptionally rare pattern. A systematic investigation of the mechanisms through which intense rainfall triggers landslide is therefore crucial for effective disaster prevention and mitigation.

Methods Based on detailed field geological investigations and finite-element numerical simulations using Geo-Studio, a multi-field seepage–stress–displacement coupled model of the Wanshuitian landslide was developed. The model was used to reconstruct and analyze the hydrological response of the landslide to the short-interval, multi-peak rainfall events. Combined with the regional geological environmental conditions, the causative mechanisms and failure modes of the landslide were clarified.

Results The results indicate that: (1) The superimposed rainfall sequence of “intense rainfall - short interval (4 days) - subsequent rainfall” within 17 days prior to the failure was the primary external cause leading to instability. (2) The lag effect of rainfall infiltration, together with water accumulation within the slip zone and the consequent softening-induced sudden unlocking of the rock–soil mass, constituted the key triggering mechanism. (3) Under two consecutive rounds of persistent heavy rainfall, pore water pressure in the slope increased continuously, while effective stress declined progressively, ultimately causing a significant reduction in the shear strength along the sliding surface and resulting in failure. The maximum increase in pore pressure reached 184.8 kPa, the maximum drop in effective stress was 161.39 kPa, and the overall reduction in shear strength reached 149.8 kPa. (4) The deformation evolution of the Wanshuitian landslide exhibited both progressive and abrupt movements, with the failure mode being a combination of wedge-shaped sliding formed by the mutual cutting of multiple joint sets and rock layers.

Conclusion Based on these findings, targeted prevention and mitigation strategies are proposed for the Wanshuitian landslide and similar types of rainfall-induced landslides. The research findings provide theoretical support and scientific guidance for monitoring, early warning, and engineering control of analogous geological hazards.