Abstract: To investigate the stability of the surrounding rock during excavation process of the underground caverns at the Baihetan hydropower station, effects of excavation unloading on the deformation and failure of the surrounding rock using the numerical simulation software 3DEC based on DEM (discrete element method) are analyzed. The microseismic monitoring technology is introduced to monitor and analyze micro-fracture evolution inside the surrounding rock of the caverns in real time, and the numerical simulation results are compared with the microseismic monitoring data. In order to verify the accuracy of numerical simulation and microseismic monitoring results, the spatiotemporal evolution law of the macro-deformation of the surrounding rock is studied by conventional displacement monitoring. The results show that the damage of surrounding rock is closely related to the on-site construction state and also affected by various geological structures. The deformation characteristics of the surrounding rock obtained by numerical simulation are basically consistent with the aggregation rules of microseismic events obtained by microseismic monitoring, and the results are in good agreement with the conventional monitoring results. The comprehensive research method combining the three-dimensional discrete element numerical simulation and microseismic monitoring technology can better describe the mechanical behavior of the surrounding rock under excavation unloading, and effectively evaluate the damage characteristics and potential risk areas of surrounding rock.

Key words: stability of surrounding rock, discrete element method, numerical simulation, excavation unloading, microseismic monitoring