A Microseismic Method for Dynamic Warning of Rockburst Development Processes in Tunnels

Early warning of rockbursts remains a worldwide challenge in rock engineering. In this work, a microseismicity-based method of rockburst warning in tunnels is proposed to warn of and reduce the risk of rockburst. The method uses real-time microseismic data and an established rockburst warning formula to provide dynamic warning of rockburst risk during excavation of a tunnel. The establishment of the rockburst warning formula involves several key parts. These include a rockburst database, selection of typical rockburst cases, functional relationships between microseismicity and rockbursts, optimal weighting coefficients, and dynamic updating. By using the proposed method, the probability of strain and strain-structure slip rockbursts of different intensity (extremely intense, intense, moderate, slight, and none) can be warned of in real time. The method has been successfully applied to rockburst warning in deeply buried tunnels at the Jinping II hydropower project (about 11.6 km in total for D & B tunnels). This success illustrates the applicability of the proposed method. In addition, it is found that during the rockburst development process, the microseismic eigenvalues for strainbursts are bigger than in strain-structure slip rockbursts of the same intensity.