Analyze of the Affection of Excavation Unloading of the Rock Mass of the Spillway Tunnel of a Hydropower Station on the Slope’s Stability

After the excavation of the rock , the rock mass stress state changes and the quality of rock mass damage deterioration. Rock excavation of spillway tunnel of the hydropower station may have some influence on the stability of the tunnel-face side slope. In this paper, combined with the engineering practice, based on the unloading rock mass theory and through two dimensional finite-difference method. Selected seven feature points near the excavation surface as monitoring points for calculation ,then calculated the effect on the stress and strain of the slope caused by the excavation of the spillway tunnel and analysed the changes in the distribution of the slope rock mass plastic zone and the point factor of safety. The results show that spillway tunnel excavation in excavated slope have some impact on the excavated slope stability, and it is more obvious for the effect on stability of excavated slope in considering rock mass unloading effect than do not consider the rock mass unloading effect.