Dynamic analysis of rock mass deformation in large underground caverns considering microseismic data

The underground powerhouse of a hydropower project is one of the most significant structures that will be permanently in use. Large scale excavation induced rock mass damage may pose a threat to the stability of the underground powerhouse. In the present study, a microseismic (MS) monitoring system was established to capture microcracks induced by excavation of the underground powerhouse caverns at the Houziyan hydropower station. Based on tempo-spatial characteristics of the MS events, the relation between MS activities and field construction was analyzed and the main damage regions were revealed. A damage-driven model considering the effect of MS source sizes is adopted for dynamic analysis of rock mass deformation of the underground caverns. The rock mass damage is simulated by a micro-mechanics-based constitutive model described by the fracture density determined by the MS source radius. A numerical model of a typical profile of the underground powerhouse was established. The MS data monitored in each bench excavation period of the underground powerhouse caverns was imported to the numerical model for dynamic analysis of deformation. The results showed that the effect of rock damage played a significant role in the rock mass deformation of the underground powerhouse during each bench excavation. The displacements of rock mass considering MS data obtained from the numerical analysis can provide better predictions for real conditions on site.