Stability Analysis of Fault and Free-Surface Cut Rock Blocks at the Vault of Large Underground Powerhouses

To address the safety concerns of vault surrounding rock damage induced by rock blocks under high-stress conditions of underground powerhouses, a microseismic (MS) monitoring system was established. This study investigates the spatiotemporal evolution of MS events in the vault, the associated fracture patterns, and the correlation between MS events and surrounding rock damage during the excavation of the underground powerhouse. The spatial evolution patterns of the stress field, displacement field, and fracture field during the process of vault surrounding rock damage were revealed. The research results indicate that: 1) The presence of fault and free-surface cut rock blocks at the vault of the main powerhouse enhances the disturbance effect of excavation on the surrounding rock; 2) MS events exhibit localized clustering characteristics in space, with certain clusters highly coinciding with the location of the vault rock blocks. The MS activity characteristics in the regional rock mass, can serve as a qualitative indicator for early warning of surrounding rock deformation; 3) The combination of MS monitoring and numerical simulation effectively identifies surrounding rock damage information in the rock block areas of underground powerhouses. The research findings can serve as a reference for analysing surrounding rock damage and stability in similar engineering projects.