Stability analysis and reinforcement evaluation of high-steep rock slope by microseismic monitoring

The stability of excavated high-steep rock slopes is most significant in the long-term safety of large-scale hydropower projects. Dagangshan rock slope had an unloading fractured zone (XL-316) and a fault (f231) during excavation, which resulted in a high risk of slope instability. Anti-shear tunnels were constructed for enhancing the overall shear resistance and reinforcing the slope at six different elevations. The microseismic technique was employed to investigate microseismic activities during excavation and after reinforcement. An integrated method of microseismic energy density and the magnitude-frequency relation based on microseismic monitoring was proposed to analyse the stability and reinforcement effect of the slope. During excavation, a large number of microseismic events took place with few low-magnitude events and numerous high-magnitude events. The aggravated damage occurred in the major discontinuities during excavation. The number of low-magnitude microseismic events increased after reinforcement, and the b value obviously increased, which means the slope stability was substantially enhanced. Microseismic activities were evidently reduced, and the accumulated microseismic energy increased slowly. The stresses were transferred towards the edge of the anti-shear tunnel, and a small number of low-energy events occurred. The targeted reinforcement has served well for its purpose and improves the mechanical performance of the discontinuities. The application of the proposed method was verified by 3D RFPA-Centrifuge software. The proposed method can be considered as an effective way to evaluate the reinforcement effect and stability of high-steep rock slopes.