Abstract: The geological conditions of the left abutment slope of Yangfanggou Hydropower Station are complex, and the unloading effect in the rock mass developing with slope-oriented steep-gentle-dipped fractures is strong. During the excavation of the slope, the deformation and the cracking response in the rock mass on the upstream side of the arch dam foundation are observed, the stability of the slope and personnel safety have been significantly affected. Based on the engineering geological survey and monitoring data analysis, a discrete element simulation model is established for the deformation mechanism and the crack cause analysis of the left abutment slope. The numerical analysis results show that: the fault f27 and the slope-oriented structural plane with gentle dip are the main factors that influencing the deformation response during excavating the slope. During the excavation of the slope above E.L.2000 m, the f27 has an obvious influence on the local stress at the toe of the slope. The stress will be concentrated in the upper part of f27 firstly and then unloading and relaxed under the combined action of the slope-oriented structural plane. The shear deformation happens along with the fault f27, and the subsidence of its hanging wall caused the crack of the rock mass. The slope stability will be significantly reduced with the f27 exposed on the excavation face, there is a large risk of slip and instability. The pre-stressed ground anchors are used to establish the toe and strengthen the middle of the slope, which can effectively improve the stability of the slope and control the shear deformation of f27. After the prestressed ground anchors are applied, the safety factor of the slope is increased from 0.98 to 1.20, and the monitoring data show that the deformation is controlled successfully.

Key words: Yangfanggou Hydropower Station, High Rock Slope, Deformation and Failure Mode, Crack Cause, Reinforcement Design, Stability Analysis