Abstract: The Dagangshan hydropower station dam abutment slope stability has been studied based on the theory of unloading rock mass. Based on the large-scale universal finite element program ADINA, for the conditions of different earthquake accelerations, different anchoring lengths and tonnages of unloading dam abutment slope, the displacements of key points, stresses and plastic zones change rule are comparatively analyzed; and it is pointed out that the slope deformations are composed of two parts; one part is unloading rebound, the other part is the compressive deformation of inner facing slope induced by applying large tonnage anchors. Research shows that because of the cable through the V-shaped rock bottom line, in the possible shear zone of landslide there formed a strong resistance sliding key, so that increasing cable length or tonnage can effectively reduce the plastic zone of the abutment; for accelerations of 0.1g and 0.15g in the earthquake, in different reinforcements of tonnages, may form transfixion of plastic zone. Under different earthquake accelerations effected by different anchorage length and anchoring force, the horizontal displacements of different key points presented linearly and nonlinearly changing; inflection point in the nonlinear relationship should be paid attention to. To reduce the plastic zone of rock mass, it is better to increase anchorage length in the same proportion. In order to effectively reduce the plastic zone development during strong earthquake, the 120% increase in anchor length is suggested.

Key words: slope excavation, earthquake acceleration, unloading rock mass theory and method, anchor optimization, anchor length and tonnage