Various types of sedimentary deposits are widely distributed in the mountainous areas of northern Guizhou, among which landslide deposits are the most common. A landslide deposit on the inner side of a highway in the region was analyzed. The mechanism and evolution mode of rainfall disasters in the deposit was studied through refined investigation and measurement, numerical simulation and other techniques. The landslide accumulation body was affected by multiple rounds of rainfall in the early stage, and the shallow surface of the slope has experienced multiple local instability and damage, resulting in cracks in the mortar retaining wall, burial of the concrete retaining wall, severe damage to the road surface structure, and difficulty in passage. Under later rainfall conditions, there is still a possibility of local instability or even overall instability. The numerical simulation results of rainfall show that the accumulation body is in an unsaturated state in its natural state. Continuous heavy rainfall will promote the development of the soil from unsaturated to saturated state. During the rainfall process, the transient saturation zone gradually expands and deepens from the slope surface, and by the end of the rainfall, the entire slope soil body has almost reached saturation state. Affected by the water barrier effect of bedrock, infiltrated rainwater collects at the interface between the foundation and the cover, and pore water continuously migrates towards the foot of the slope under the action of gravity, resulting in high pore water pressure at the interface and foot of the slope. On the one hand, the lubrication and softening of gravel soil by pore water promote the structural weakening and mechanical strength attenuation of the soil. On the other hand, high pore water pressure plays a role in reducing the effective stress of the soil, resulting in a decrease in the anti sliding force of the slope, which in turn leads to overall sliding along the foundation cover interface. However, the process of accumulation body developing into landslide under heavy rainfall can be divided into four stages, namely: ①full rainfall infiltration, ②partial saturation of slope surface, ③expansion of saturated area, local instability, ④overall instability and damage. In the early stage, multiple local instability and damage only developed to stage ③. In the later stage, if such heavy rainfall or even extreme rainstorm occurs, the colluvial accumulation body is very likely to have overall damage, which will cause complete road blocking and threaten pedestrians and vehicles in the process.

colluvial deposits  /  heavy rainfall  /  seepage field  /  failure mechanism  /  evolution mode