Comprehensive evaluation of excavation-damaged zones in the deep underground caverns of the Houziyan hydropower station, Southwest China

The disturbance of a rock mass by blasting or stress redistribution can significantly influence the overall performance of an underground excavation. The characteristics of excavation-damaged zones (EDZs) during the excavation of underground caverns at the Houziyan hydropower station in Sichuan Province, China, were investigated using various in situ tests. This study presents a comprehensive evaluation of the evolution of EDZs in the surrounding rock mass in the underground powerhouse caverns using microseismic (MS) monitoring and conventional testing methods, including multi-point extensometers, acoustic wave testing and borehole TV. First, by analyzing a series of conventional testing and MS monitoring results, the deformation and failure characteristics of the surrounding rock mass were determined. Next, the formation mechanisms of fractures in the surrounding rock mass subjected to excavation-induced unloading in the underground powerhouse caverns were determined. The relationships between the EDZs of the surrounding rock mass, crack evolution and construction status were then analyzed to investigate the crack formation, development and coalescence processes. Finally, the thicknesses of the EDZs were quantitatively determined, the relationships between the fracture evolution and construction progress were established, and the EDZ formation and evolution mechanisms were evaluated. The results not only provide direct data for geological exploration but also contribute to optimizing excavation design and support for analyzing the deformation behaviors of underground powerhouse caverns.