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.