Abstract: Erguxi toppling slope is located in the reservoir area of Shiziping hydropower station in Sichuan Province. On September 2013 the storage water level was raise up to 2 540 m and the slope deformed strongly and then blocked G317 road. Preliminary analysis shows that during the rapid cutting of valley, the stress release in rock mass leads to displacement towards the free face, and because of hard rock and soft rock, the deformation is uncoordinated. The deformation of soft rock is lager than that of hard rock, resulting in the stress concentration in hard rock, and when the stress is larger than the hard rock strength, hard rock failure happens. The 5.12 Wenchuan earthquake together with highway excavation and rainfall further exacerbated the toppling slope, and then the slope gradually reached a state of stress balance. According to field geological survey, we analyzed the formation mechanism of the toppling slope by means of drilling core and monitoring. Results reveal that the slope is in the early stage of toppling of interbedded soft and hard rocks. The damage of slope rock mass was caused by earthquake and was intensified by water storage and rainfall. At present the slope is in stress adjustment and the deformation will continue for a long period, and also water level rise will no doubt exacerbate its deformation.

Key words: Shiziping hydropower station, toppling slope, Erguxi slope, earthquake, storage, monitoring, formation mechanism