Nucleation process of rockbursts based on microseismic monitoring of deep-buried tunnels for Jinping II Hydropower Station

To study the rockburst nucleation and evolution process in deep-buried tunnels for Jinping II Hydropower Station, a microseismic real-time monitoring system is established to monitor diversion tunnel No.3 during TBM excavation. Based on a great deal of microseismic monitoring data, the characteristics of spatiotemporal distribution, activity rate, exhausted energy, energy density and apparent volume of microseim are comprehensively considered before occurrence of rockbursts. What's more, the initiation, propagation, extension and inter-coalescence mechanisms of microcracks during progressive nucleation process of rockbursts at Jinping II Hydropower Station are revealed. The spatial relationship between evolution rules of microseismic activities and rockbursts is discussed. The monitoring results show that precursory microcracking exists prior to most rockbursts, which can be captured by the microseismic monitoring system. The event rate, microseismic released energy and accumulated apparent volume have their different increase tendencies before rockbursts. The energy source of some rockbursts is composed of local energy and transfer energy, namely Edrive source =Elocal+Etransfer, and a portion of rockbursts can be induced by certain adjacent violent rockbursts at the same time. It is feasible to monitor and predict rockburst events by using the microseismic monitoring technology for deep-buried tunnels.