Rockburst and microseismicity characteristics in the Qinling water conveyance tunnel of the Hanjiang-to-Weihe River Diversion Project

The Qinling water conveyance tunnel of the Hanjiang-to-Weihe River Diversion Project is the first one to overgo the Qinling Mountains with the maximum burial depth of about 2000 m, and the project is seriously threatened by rockburst hazards. The microseismic monitoring technique capable of capturing microcracking and estimating damage of rock, was employed to monitor and predict rockbursts in the deep tunnel. To study the rockburst characteristics in the Qinling water conveyance tunnel, spatial distribution of 298 rockbursts at chainage K33 + 873.3 to K36 + 979.6 along the tunnel axis, in the cross-sectional direction, and relative to the working face was examined. Microseismic sequences and energy release of associated microseismic events for rockburst of different intensities were quantified to provide reference for predicting rockburst occurrence and intensity. Evolution of an intense rockburst in the #4 sub-tunnel of the Qinling water conveyance tunnel was interpreted by the source parameters and spatial-temporal distribution of microseismic activities. According to the statistical analysis of rockburst prediction, rockburst occurrence and location in the Qinling water conveyance tunnel were satisfactorily predicted with high success rates based on sufficient volume of microseismic data. This study is critical for rockburst management over the construction of the unexcavated Qinling water conveyance tunnel, and provides insights into rockburst control in other deep, hard-rock excavation projects.