Deformation characteristics and damage evolution analysis of weak interlayer zone in fractured underground cavern

The stability of surrounding rock is deteriorated due to the characteristics of Weak Interlayer Zone (WIZ) in underground caverns. To address the deformation and small-scale collapse issues during the construction of a hydropower station’s underground caverns, this study combined on-site investigations with theoretical analyses. A comprehensive multi-parameter monitoring system was established, including microseismic monitoring, multi-point extensometers, bolt stress meters, and borehole television, to elucidate the deformation characteristics and damage of the weak interlayer zone. First, the distribution characteristics of multi-parameter of WIZ in tailrace surge chamber during small-scale collapse were analyzed. The internal relationship between this multi-parameter and the WIZ instability process was discussed. Second, fracture characteristics, microseismic source characteristics, and local stress of the rock mass during deformation and failure of WIZ were presented based on moment tensor inversion. Then, the correlation between multi-parameter before and after WIZ collapse was investigated through coupling analysis. Finally, the failure mode of the rock mass within the WIZ range was determined, and the deformation characteristics of WIZ were explored. The research results can provide some references for understanding surrounding rock mass damage and failure mechanisms in underground caverns with WIZ. It can also guide the design and optimization of excavation and support systems for similar projects.