Research on the Criteria for Identifying Damage Zones during Excavation of High Stress Brittle Hard Rock Caverns

The deep buried large underground powerhouse cavern group of Shuangjiangkou Hydropower Station is arranged in the left bank mountain, and the geological lithology is brittle hard rock granite. The measured ground stress reaches 37.82 MPa, which is a high to extremely high stress zone. Research has found that the relaxation depth of underground power plants ranges from 2.2 m to 4.4 m, and the overall damage to surrounding rock shows an increasing trend with layered blasting excavation. However, the relaxation depth variation is small, and the average fragmentation variation of the relaxation layer is less than 10%. The lag effect of surrounding rock fracture is shortened. The GEDZ distribution in high stress brittle hard rock caverns can be evaluated using acoustic detection as the main method, supplemented by innovative semi quantitative indicators such as "rupture morphology"（new cracks, residual blasting hole half hole rate, rock burst failure depth）, and quantitative indicators such as permeability to reasonably evaluate the distribution of excavation damage areas in surrounding rock. This can better guide on-site design and construction, and provide reference for similar hydropower underground power plants and Sichuan Tibet Railway projects in the future.