The underground powerhouse of Houziyan hydropower station is a typical deep-buried powerhouse, with the depth of 280m~510m horizontally and 400 m~660m vertically. The ground stress is high and the geological conditions are very complicated. In order to monitor and analyze the surrounding rock mass stability during continuous excavation of the underground powerhouse and locate the potential instability failure areas, an ESG (Engineering Seismology Group) microseismic monitoring system manufactured in Canada was installed in April, 2013. The wave velocity range of the rock mass in the underground powerhouse was measured by the digital acoustic instrument. The overall equivalent wave velocity of the monitoring system was determined through the blasting tests. The seismic source location error was less than 10 m. The microseismic event waveforms were manually processed to acquire high position accuracy and the interference events were filter out. Combining the temo-spatial distribution regularity of the seismic events with field observation, micro-fracture clusters and potential instability failure areas of the underground powerhouse were identified and delineated. The results could provide references for later excavations and supports of the underground powerhouse. Furthermore, a new research idea is opened up for the stability analysis of the deep-buried underground powerhouse subjected with excavation-induced unloading.

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