Microseismic Monitoring of Rock Mass Fracture Response to Blasting Excavation of Large Underground Caverns Under High Geostress

Large underground caverns are characterized by high geostress, high sidewalls and complex geological conditions, which make the rock masses suffer a series of failures in the process of excavation. The excavation of the large underground powerhouse of the Baihetan Hydropower Station in China is based on the drilling and blasting method with small steps and weak-vibration blasting. To thoroughly understand the mechanism of blasting excavation on the surrounding rock, in situ microseismic (MS) monitoring system was established to analyze the blast-induced microseismicity of the large underground powerhouse of the Baihetan Hydropower Station. The waveform characteristics of blasting events and rock fracturing events are distinguished first. Then, the spatial distribution of density contours of MS events and rock mass seismic deformation induced by blasting excavation are obtained. The results show that the blast-induced risk areas are mainly concentrated in the downstream sidewall of the underground powerhouse. MS monitoring in real time during the excavation process can provide data reference for the dynamic optimization of on-site construction schemes.