Abstract: Rainfall has induced many landslides of soft rock in Northwest China. To reduce the loss caused by this kind of disaster, based on the old landslide of Caijiapo town, two groups of centrifuge model tests with different hydraulic actions were conducted through the combination of geological analysis and simulated rainfall centrifuge model test, and the influence of hydraulic action on the initiation mechanism of the slope was discussed. The results show that: i) The soft rock slope is destructed by hydraulic action in a multi-staged and progressive way, and the deformation process includes the initial deformation stage, the accelerated deformation stage, and the flowing failure stage. ii) The pore water pressure obviously accumulates due to the seepage and diffusion of water towards the structural plane and the surface. Water mainly accumulates in the tensile cracks of steepened micro-geomorphologic area and areas with severe compressional deformation at the foot of slope. iii) In a short time, the increment of pore water pressure increases with time, causing the sliding mass fluidized. Therefore, in the process of disaster risk prevention and control, it is necessary to strengthen the monitoring of pore water pressure growth rate in fractured area.

Key words: soft rock, landslide, hydraulic action, startup mechanism, centrifugal model test