Characterizing Rockbursts Along a Structural Plane in a Tunnel of the Hanjiang-to-Weihe River Diversion Project by Microseismic Monitoring

Rockbursts pose serious threats to the safety of personnel and equipment in tunnels of the Hanjiang-to-Weihe River Diversion Project. Small-scale structural planes around the tunnel play an important role in controlling the occurrence and intensity of rockbursts. To study the characteristics and evolution of rockbursts along a structural plane, three successive, intense rockbursts in the #4 sub-tunnel were summarized in detail and investigated by analyzing 492 recorded microseismic events. The rockbursts were closely related to the structural plane, because most events had a ratio of S-wave energy to P-wave energy larger than 10 and were associated with shearing along the existing structural plane. The statistical parameters, which include the energy index, cumulative apparent volume, and b value, were used to analyze the evolution of the three rockbursts. Quantitative interpretation of the source parameter and statistical parameters for a given microseismic data set provided a significant insight into characterization of rockbursts along the structural plane. In addition, some distinctive seismic precursors for rockbursts along the structural plane were acquired; therefore, rockbursts along the structural plane may be effectively predicted based on these seismic precursors. Preliminary results in the current study are valuable for predicting and mitigating rockburst hazards in tunnels with similar conditions.