Abstract: The intense geological structure and complex rock mass conditions in western China pose significant challenges to the construction of large underground cavern groups, including sudden changes in surrounding rock deformation and diverse failure modes. To address this issue, this study focuses on the underground cavern group of the Yingliangbao hydropower station in the Dadu River Basin, summarizing the typical stress-structure type failure modes of underground cavern groups under medium to high stress conditions, analyzing the impact of the September 5, 2022 Luding earthquake on the stability of the surrounding rock, and proposing engineering control strategies for stress-structure type rock mass failure. The study reveals that: 1) after excavation, 90% of the monitoring points showed surrounding rock deformation values less than 100 mm, with the deformation following a log-normal distribution; 2) under excavation unloading, the surrounding rock deformation curve of the Yingliangbao underground cavern generally exhibits a gentle step-like growth pattern, but rock mass deterioration can lead to a sudden increase in deformation, with a daily deformation exceeding 90 mm, highlighting the hard, brittle, and heterogeneous deformation characteristics of the Yingliangbao granite; 3) the overall anchorage load exhibits a normal distribution, with areas of higher anchorage load corresponding to areas of greater deformation; 4) the September 5 Luding earthquake had a relatively minor overall impact on the three major caverns, but may have adverse effects on the support structures near stress concentration zones or discontinuities; 5) the excavation of underground caverns faces challenges such as frequent shallow failures and high costs for addressing deep failures, with failure modes including stress-type, structure-type, and stress-structure type failures, dominated by stress-structure type failures. To address the surrounding rock failure issues at the Yingliangbao underground cavern group, this study proposes the “pressure maintenance-reinforcement” principle for underground cavern support, and verifies the effectiveness of “precision blasting + rapid shotcrete + timely pre-stressed anchors” in inhibiting shallow rock mass deterioration and “fine layering + high-tonnage pre-stressed anchors” in inhibiting mid-deep rock mass deterioration, providing a reference for the construction of large underground caverns in western China.

Key words: underground cavern, seismic response, surrounding rock deformation, failure mode, control strategy