Abstract: This study aims at revealing the deformation and evolution characteristics, formation mechanism and stability of slope under rainfall infiltration condition. A slope in the north stope of Taihe mine in Xichang city, Sichuan province was analyzed in detail as a research object by adopting various methods such as field geological survey and mapping, in-situ test, laboratory test and numerical simulation. The results show that: 1) Both landslides in 2018 and 2019 occurred in rainy season and stabilized again with the end of rainy season. 2) The formation of the landslide is the result of the comprehensive action of multiple factors: the fault provides the boundary for the formation of the landslide, which is the external condition; the diabase with high content of chlorite and montmorillonite is easy to soften and disintegrate when exposed to water, which is an internal condition; the mining and rainfall are the inducing factors. Mining forms an ultra-high slope and exposes the diabase rock layer, while rainwater infiltrates from the slope surface and fault to erode and soften the whole diabase rock layer, resulting in local sliding of the diabase layer under the action of high potential energy, and then pulling it to the overall sliding. 3) Rainfall greatly impacts on the factor of safety and failure mode of slope. The slope is in a stable state before rainfall, and the potential failure mode is overall sliding. After 5 days of rainfall, the factor of safety for the slope drops to 0.842, and two steps of local sliding occurs in the diabase layer. After that, the factor of safety continues to decrease, and the damage range further expands, which is confirmed by the actual observations.

Key words: mine slope, diabase, deformation evolution law, formation mechanism, unsaturated seepage