Stability analysis of surrounding rock mass in underground powerhouse considering damage effect of microfractures

A high-precision microseismic(MS) monitoring system was built to monitor surrounding rock microfractures in the underground powerhouse on the left bank of Shuangjiangkou Hydropower Station. The surrounding rock damage area with spatiotemporal clustering of MS activities was studied for qualitative analysis of the damage mechanism of surrounding rock microfractures, based on the source parameters of MS events. The surrounding rock microfracture scale characterized by the source radius of MS events was considered to establish the constitutive relation. MS information was imported into the model for numerical analysis using fast Lagrangian analysis of continuain 3 dimensions(FLAC3D). The results indicated that the numerical simulation results considering MS damage can better reflect the actual situation of the field. The surrounding rock microfractures mainly showed mixed failure characteristics.Shear failures appeared in localized areas while the fracture scale of sections from K0-33 m to K0-15 m on the vault was large. The deformation increment caused by microfracture damage in the shallow surrounding rock of the top arch accounted for 10%-13%, and the stress decrement in the surrounding rock caused by microfracture damage accounted for about 10%.