Stability analysis and reinforcement scheme of a deformation rock mass for Xigu hydropower station based on NMM

The deformation rock mass No. 2 locating at the left bank of plunge pool at outlet of diversion tunnel of Xigu hydropower station on the Jiulong river in Sichuan Province, China, is about 155 m in transverse width, 445 m in slope length and 41 m in average thickness, failure of which will fatally affect on the station operation. The NMM with the mathematical mesh and the physical mesh is a newly developing and promising approach, having a big advantage in calculating the continuous, discontinuous or large deformation. By use of the numerical manifold method (NMM), the limit friction angle of the deformation rock mass, is calculated by the intension-reduce method, and the failure mechanism is analyzed and demonstrated. Then the safety factors of slope stability are obtained under the normal working condition, earthquake working condition and rainstorm working condition. Considering the engineering measures, such as excavation unloading, pre-stressed anchor ropes and anti-slide holes, etc., the effects of several different reinforcement schemes on the slope stability are analyzed and compared. Finally the reasonable reinforcement scheme, which combines anti-slide holes with prestressed anchor ropes and some other measures for preventing the rainfall infiltration, is offered for reinforcing the deformation rock mass. After reinforcement, the stability of the deformation rock mass No. 2 can meet the design requirement according to analysis.