Deformation Mechanism and Crack Cause Analysis of the Left Abutment Slope of Yangfanggou Hydropower Station

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 slope, the deformation and cracking response in rock mass on the upstream side of the arch dam foundation have been found successively, the stability of slope and personnel safety has been significantly influenced. Based on engineering geological survey and monitoring data analysis, a discrete element simulation model is built for deformation mechanism and crack cause analysis of the left abutment slope. The calculation results show that: the fault f27 and slope-oriented structural plane with gentle dip are the main factors that influence the deformation response during excavating the slope. During the excavation of the slope above E.L.2000m, f27 has an obvious influence on the local stress at the foot 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 f27 exposed on the excavation face, there is a large risk of slip and instability. Pre-stressed anchor cables are used to stablish the foot and strengthen the slope half, which can effectively improve the stability of the slope and control the shear deformation of f27. After the pre-stressed anchor cables 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.