Abstract: The right bank underground caverns of Wudongde hydropower station are dense and large-scale, and the geological stratification is complex, which results in severe deformation and failure problems during excavation. Based on the analysis of the characteristics of geologic framework, in-situ stress data and excavation consequence of underground caverns, a numerical model was established to investigate the stability of the right bank underground powerhouse during excavation unloading by using the discrete element method (DEM). In the numerical modelling, we studied the principal stress fields and deformation fields, and analysed the deformation mechanism of the structural planes with a steep dip angle. Then, a high-precision microseismic (MS) monitoring system was established to evaluate the stability of the surrounding rock during excavation. Their assembling rules of MS events and energy ratio Es /Ep were analysed to identify the potential failure regions and deformation mechanism. The combined numerical simulation and MS monitoring indicated that under the excavating unloading, the failure of rock masses was observed near the layered rock with the steep dip angle where MS events assembled and the energy released, which results in surrounding rock failure. The deformation of surrounding rock was largely induced by stress-driven tensile failure which was controlled by structural planes. The results provide important references for excavation and reinforcement of the right bank underground caverns at Wudongde hydropower station.

Key words: underground powerhouse, distinct element, layered rock mass, microseismic monitoring, deformation