Failure Mechanism of the Toppling Rock Slope with Different Numbers of Free Faces Caused by Excavation: a Case Study in Jiacha Hydropower Station (China)

Toppling failure is a widespread failure mode in natural and excavated rock slopes and threatens the construction and operation of important infrastructure, such as hydropower and transportation corridors in southwest China. Therefore, comprehending the mechanisms underlying toppling is essential for predicting and preventing relevant landslides. In this study, external deformation monitoring equipment, multipoint deep displacement meter and data acquisition equipment were conducted on the study area to explore the failure model and deformation characteristic of the toppling rock slope with different numbers of free faces. The field monitoring results suggested that the groundwater and unloading effect caused by excavation initiated this slope with one free face, which subsequently deformed gradually at a constant velocity. Thereafter, the displacement vectors progressed toward the free face, and the rock layers gradually slanted downslope. After the slope failed, it was separated into two sections with double and three free faces, respectively. The failure models of these two sections were analyzed numerically, and the results show that the deformation of the double free faces rock slope is primarily caused by wedge sliding along the intersection line of two discontinuities; the three free faces rock mass slope may bend first and then slide along a discontinuity. The study deepens the understanding of toppling rock slopes and provides a theoretical framework for anticipating and avoiding the deformation trends of such slopes.