Abstract: Many faults propagate near the underground powerhouse of Dagangshan power station. Rockmass stability of the underground powerhouse is controlled by two steep angle faults which are extended through the middle and rear parts of the powerhouse. The collapse area near the fault was found when the fault extended through the vault was excavated. So it is necessary to monitor the stability of the powerhouse and collapse area near the faults. The integrated seismic system(ISS) of South Africa is established to monitor the area in October 2010. The unattended system run automatically, which also can be controlled and diagnosed remotely. Four methods such as spatiotemporal distribution method, magnitude level method, energy index method and dislocation method are used to analyze the stability of the collapse area, side walls and the rock mass near the structure plane. The research results show that the underground plant is overall stable and safe. Few seismic events and low magnitude near the collapse area can be got from seismic monitoring data. Two side walls are stable because the number of the seismic events and dislocation slip of the rock mass are small. The slide displacement between the structural planes is scattered and small. And the rock of the fault plane is inactive. Therefore, the stability of collapse area is increased and less influenced by faults after the rock is reinforced by the anchor. It is of guide significance to use microseismic monitoring to assess the stability of power house during the running and construction stages.

Key words: microseismic monitoring, hydropower project, underground powerhouse, collapse empty area, fault, stability