Stability analysis and movement process determination of rock masses under open-pit to underground mining conditions

Underground mining under an open-pit slope results in movement and instability of rock masses. However, most rock mass movement prediction methodologies are empirical and only suitable for underground mining. In this paper, a new theoretical methodology is proposed to predict the movement and instability of rock masses caused by open-pit to underground mining, combining two influences, open-pit slopes and underground mining. Considering the influence of open pit on damage patterns, a double-slip surface deflection failure model is proposed and compared with the rock mass movement model under underground mining conditions. The critical value of sliding body area and double-slip surface location were derived based on the limit equilibrium state determined using the vector sum method, and verified by a particle flow program. Additionally, base friction model tests were used to assess the suitability of the theoretical model in rock mass damage processes. The rock mass moving boundary under open-pit to underground mining conditions were discovered to be deflected and sliding body area larger than under underground mining conditions. The movement process was bottom goaf collapse-middle deflection-top cracking, and the damage pattern a traction landslide passing from goaf to surface, which differed from uneven subsidence caused by underground mining. These results revealed that the proposed failure model was most reasonable for predicting rock mass movement under open-pit to underground mining conditions.