Microseismicity and focal mechanism of blasting-induced block falling of intersecting chamber of large underground cavern under high geostress

Block falling is a rock mass damage disaster that is easily encountered during the excavation of underground caverns. To objectively assess the microseismicity and focal mechanism of block falling of underground intersecting chamber induced by blasting excavation, an array of six uniaxial accelerometers and eight uniaxial geophones were installed around the busbar chamber of underground cavern group of the Baihetan Hydropower Station in China. In the time domain, the seismicity response to production blasting reveals that within 3 h after blasting, microseismicity is in an active phase. In the spatial domain, with the advance of working face, the concentrated stress is distributed around the excavation region, and the damage and deterioration of the rock mass are gradually intensified. The active area of microseismic (MS) events is consistent with the stress concentration region. By analyzing the fracture mechanism based on the moment tensor inversion method, it can be seen that the fracture mechanisms of block falling of the intersecting chamber are dominated by tensile fracture. The research results could provide crucial guiding reference for stability analysis, as well as for rethinking the blasting excavation and support optimization of rock masses in similar large underground cavern.