Microseismic monitoring and stability analysis of the right bank slope at Dagangshan hydropower station after the initial impoundment

The right bank slope of the Dagangshan hydropower station in China has suffered from reservoir water pressure and seepage effects since the initial impoundment process. This paper describes the microseismic monitoring system and impoundment process of the Dagangshan hydropower station. Microseismic activity was detected in the right bank slope after the initial impoundment by the microseismic monitoring system. The spatiotemporal characteristics of the microseismic events and the piezometer monitoring results are used to confirm the conductive seepage pathways, the porous rock mass and the water recharge source in the right bank slope. Based on the geological conditions of the porous rock mass identified by microseismic and piezometer monitoring, a simplified two-dimensional (2D) finite element model is developed. A 2D finite element analysis is then applied to explore the damage mechanisms of local regions of the right bank slope after the initial impoundment. In addition, the load/unload response ratio theory is used to predict the failure of the slope based on the seismic source information obtained by the microseismic monitoring system. According to the actual geological conditions of the right bank slope, a simplified 3D numerical model is developed for the stability analysis of the right bank slope after the initial impoundment. Based on the porous rock mass identified by the microseismic monitoring, the effective stress is considered in the stability analysis. The safety factor of the right bank slope including the effective stress is 1.645, which indicates that the slope was stable after the initial impoundment. The microseismic monitoring technique can record disturbances caused by seepage effects in deep rock masses after the initial impoundment process in real time.