Failure mechanism of the slope containing coarse particle enrichment zones located at the soil–rock interface under the heavy rainfall

Internal erosion caused by seepage at the soil–rock interface with local coarse particle enrichment zones (CPEZ) is a significant factor contributing to geological disasters during rainfall events. The mechanism of landslides induced by internal erosion at the soil–rock interface within CPEZ with high permeability remains unclear. This study incorporated a degradation model of bonding strength and a viscous force model into the discrete-element software MatDEM to analyze the evolution of seepage erosion at the soil–rock interface. The numerical simulations investigated the impact of the number and spacing distance of CPEZ on erosion characteristics within the interface seepage. Subsequently, the study analyzed the infiltration process and stability of the Gendakan slope during heavy rainfall to understand the failure mechanism of rainfall-induced landslides with local CPEZ at the soil–rock interface. The findings suggest that the seepage erosion process can be divided into three stages: initial, development transition, and destruction stages. Moreover, the overall permeability of the numerical model strengthens with the increase in CPEZ scale and permeability difference. A higher number of CPEZ distributed throughout the sample increases susceptibility to seepage erosion, while wider spacing between CPEZ reduces their impact on overall permeability. The numerical analysis of the Gendakan landslide highlights the importance of instability at the foot of the slope due to internal erosion of CPEZ in triggering traction landslides across the accumulation mass. This paper delves into the failure mechanism of seepage erosion at the soil–rock interface, offering theoretical support for the prevention and control of landslide geological disasters.