The instability mechanism of slab-shaped hazardous rock masses with pedestal damage—A case study of the Xueziyan hazardous rock mass

The combined effects of self-weight， karst erosion， and weathering-induced unloading accelerate differential degradation in the hazardous rock mass with pedestal damage in the Three Gorges Reservoir area. When a damaged pedestal undergoes fracturing under extreme conditions， the hazardous rock mass may fail in multiple modes， posing a significant threat to downstream reservoir areas. To investigate the influence of pedestal damage conditions on the failure modes of hazardous rock masses， this study takes the Xueziyan (XZY) hazardous rock mass in the Three Gorges Reservoir area as a geological prototype. Initially， a 3D reality model of the XZY hazardous rock mass with 0.15 m resolution was established， and the development characteristics of pedestal fissures were examined. Subsequently， the potential collapse process of the XZY hazardous rock mass was simulated using UDEC. Finally， the failure modes of the hazardous rock mass and its respective controlling factors were analyzed， and a methodological framework for stability assessment was proposed. The results indicate that: (1) The XZY hazardous rock mass initially exhibits a settlement-bulging failure mode， transitioning to sliding-toppling failure with progressive collapse. (2) The failure modes of slab-shaped hazardous rock masses are primarily governed by stress redistribution resulting from crack propagation. (3) Stability assessment of hazardous rock masses with a damage pedestal requires a dual-mechanical-index system integrating tensile/shear stability coefficients for comprehensive evaluation.