Abstract: The mechanism and effectiveness of reinforcing the right bank slope of Dagangshan hydropower station by replacing weak zones with anti-shear galleries during water storage are investigated. According to microseismic monitoring, the major damage regions in the right bank slope are identified; microseismic activities concentrates in the vicinity of anti-shear galleries at 1 240 m, 1 210 m, 1 180 m, and 1 150 m, mainly induced by tention fractures. Moreover, the stress field and displacement field during impounding are obtained by numerical simulation in RFPA (realistic failure process analysis) code to explain the microseismic activities of anti-shear galleries: stress concentration and failure are prone to occur around the anti-shear galleries which is in tension state. In association with the numerical results together with the microseismic-monitoring data, macro-shear and micro-tension are found to be the failure mode of anti-shear galleries. In the early stage of impounding, anti-shear gallery affects the stress distribution in the bank slope, and refrains from penetrative plane of fracture. Meanwhile, anti-shear gallery could enhance the anti-shear ability of bank slope; however such effect attenuates with the decline of elevation. In general, anti-shear galleries are conducive to the stability of bank slope during impoundment.

Key words: anti-shear gallery, reinforcement effect, microseismic monitoring, numerical simulation, impoundment, Dagangshan hydropower station