Study on cumulative damage mechanisms of Baihetan large underground powerhouse under blasting loads

Brittle failure of rock masses occurs frequently during blasting excavation of large underground powerhouse of the Baihetan Hydropower Station. In-situ monitoring equipments, such as microseismic(MS) monitoring, multi-point extensometers and rockbolt(cable) dynamometers, are adopted to fully reveal the mechanical responses of basalt under blasting excavation of the large underground powerhouse. The comprehensive monitoring results show that the fracture, deformation and stress of the surrounding rock increase to a certain extent after blasting excavation. Further analysis confirms that the surrounding rock deformation is compatible with the internal micro-fracture. The rock mass of the powerhouse cracks gradually under blasting excavation. The rock mass undergoes continuous fracture stages such as crack compaction, micro-fracture initiation and fracture propagation, accompanied by the growth of surrounding rock deformation. The early warning method of MS parameters based on energy index(EI) and cumulative apparent volume(CAV) can effectively warn the risk of macro-damage of the surrounding rock. It is also shown that monitoring the evolution signals of "fracture-deformation-stress" induced by blasting excavation has an important guiding role in the optimization of construction schemes of underground engineering under high-stresses as well as in the early warning of geological disasters. © 2022, Science Press. All right reserved.