Evaluation and Prediction of Surrounding Rock Stability During the Construction Period in the Underground Powerhouse of Kala Hydropower Station

Ensuring the stability of the surrounding rock is the primary objective in the construction of an underground powerhouse at a hydropower station. Real-time monitoring, stability assessment, and evolutionary trend prediction of surrounding rock deformation and support structure stress are essential for maintaining rock mass stability. Using safety monitoring data and numerical simulation, the evolutionary behaviour of surrounding rock deformation and rock bolt stress during construction of the Kala Hydropower Station underground powerhouse was analysed. Surrounding rock stability and its future state were evaluated. Deformation in the first to third layers was mainly controlled by excavation disturbance and local geological conditions. The crown within the influence zone of the F152 fault exhibited the maximum deformation of 14.60 mm, whereas deformation in other areas was relatively small. Surrounding rock deformation in the cavern remained safe. Rock bolt stress showed spatio-temporal consistency with deformation, with maximum values concentrated in fault-cutting areas. The proportion of anchor bolts with stress below 200 MPa was 96.3%, indicating that the overall stress on the rock bolts in the cavern was in a safe state. Numerical simulation results predict that significant deformation during subsequent excavation and support will be concentrated between faults F152 and F75. The maximum surrounding rock deformation may occur in the fifth-layer sidewall affected by the F75 fault. Relatively high rock bolt stress is expected in the fifth to seventh layer sidewalls influenced by the F152 fault. This study identifies potential locations and development characteristics of stability deterioration during subsequent construction, providing guidance for construction design. The results serve as a reference for surrounding rock stability evaluation and prediction in similar underground powerhouse projects.