Interpretation of generation process and precursors of successive rockbursts in a deep hard-rock water conveyance tunnel by microseismic monitoring

Rockburst pose substantial threats to safety of workers and underground structures during the construction of deep hard-rock tunnels and mines, and it has been increasing popular among the international rock engineering community in recent decades. This paper studies the generation process and mechanism of two successive, intense rockbursts in the Qinling water conveyance tunnel of the Hanjiang-to-Weihe River Diversion Project in Shaanxi province, China by analyzing the evolution of associated microseismicities and their focal mechanisms. Spectral analysis was performed using the Fast Fourier Transform (FFT) and S-transform to study the frequency-amplitude and time-frequency characteristics of recorded microseismicities during rockbursts generation process. Furthermore, the source parameters and statistical parameters, i.e., the lack of shock b value, the seismic index S value, and the cumulative apparent volume, based on limited microseismic data were analyzed to explore effective precursor for successive rockburst. This study focuses on the generation mechanism and precursors of rockbursts based on limited microseismic data, which is valuable for interpretation of the rockburst failures and prediction of successive rockbursts at short time intervals in the deep hard-rock tunnels.