Abstract: Rainfall-induced accumulation landslide is one of the most widespread geo-hazards. In recent years, due to more extreme rainfall events brought on by climate change, the scale and frequency of the rainfall-induced accumulation landslides have further increased. Centering on the slope failure mechanisms due to the extreme rainfalls, this research carries out a series of model tests in order to explore the influence of different gradations of the slope materials on the slope failure mechanism. A series of large-scale triaxial tests is carried out first, where three different colluvium materials are remolded, with the clay content fixed at 10% and the rock contents at 30%, 50%, and 70%, respectively, so that stress-strain relationships of the samples considering different gradations can be obtained. Thereafter, three slope models are built, consisting of the designed gradations. Extreme rainfalls are then applied to cause the slopes to fail, aiming to reveal different slope failure modes. Meanwhile, the changes of the water content, soil pressure, and pore water pressure inside the slope during the slope failure process are also monitored and analyzed, and the changes of fines content and its moving trajectories during the rainfall infiltration process are also illustrated. Finally, the failure mechanism of the accumulation landslide under extreme rainfall is summarized, which can hopefully provide some theoretical basis for the early warning of the accumulation landslide.

Key words: accumulation, landslide, rainfall, soil matrix, rock content, model test