Microseismicity Characteristics Before and After a Rockburst and Mechanisms of Intermittent Rockbursts in a Water Diversion Tunnel

As the buried depth of the tunnel increased, rockbursts occurred frequently during the tunnel boring machine (TBM) excavation of a diversion tunnel. In addition, multiple rockbursts occurred in the same area within a short period of time, seriously threatening the safety of workers and construction equipment. To understand the evolutionary process of intermittent rockbursts (more than one rockburst occurring in the same area), a real-time microseismic (MS) monitoring system was established. Two typical intermittent rockbursts were investigated to study the microseismicity characteristics before and after each rockburst. By further analyzing the MS event count, cumulative MS energy, energy index, cumulative apparent volume, and Es/Ep values before and after each rockburst, some seismic precursors to the two intermittent rockbursts were identified. Finally, we elucidated the mechanisms of the two intermittent rockbursts by analyzing the spatial transfer characteristics of MS events with different energies. The results of this study will be useful for intermittent rockburst warning and prevention in the construction of deep tunnels.