Microseismic Monitoring and Rockburst Characteristics in a Deep-Buried Tunnel Excavated by TBM

Rockbursts have become one of the main engineering disasters in deep-buried tunnel, seriously threatening the safety of worker and equipment. To monitor microseismic (MS) events and predict rockburst, in the present study, a MS monitoring system was established in a deep-buried tunnel excavated by tunnel boring machine (TBM). Characteristics of MS events were studied and a prediction method for intense rockburst was proposed by analyzing the temporal-spatial distribution, source parameters, and failure mechanism. The results indicated that most of MS events occurred during the tunneling process and within 15 min after a tunneling cycle completed. The MS events mainly distributed within 15 m before and after the tunneling face, and within approximate 2.0 times of the tunnel diameter. The energy of these MS events mainly ranged from 30 to 100 kJ. The prediction method based on cumulative energy index of per day and cumulative apparent volume cannot predict intense rockburst accurately in the present study, the forecast accuracy less than 60%. The proposed prediction index based on the energy index of per MS event and the apparent volume of per MS event can effectively sharpen the forecast accuracy (> 85%). The failure mechanism of MS events was predominated by tensile failure. While as the rockburst segment transited from mild to intense, the percentage of MS events of mixed failure and shear failure increased, especially shear failure events.