Study on the characteristics of rockbursts in deep-buried tunnels based on microseismic monitoring

During the construction of the Hanjiang-to-Weihe River Diversion Project, frequent extremely intense rockbursts posed a serious threat to the safety of personnel and equipment. A microseismic (MS) monitoring system, which can effectively predict rockbursts, was established to monitor the sprouting and propagation of microcracks within the rock mass surrounding the tunnel in real time. First, the MS activity characteristics of the first excavated section (K33 + 870 ~ K37 + 011) and the second excavated section (K39 + 596 ~ K41 + 602) in the south Qinling section were compared under different surrounding rock classifications. Then, the time distribution characteristics of MS events from May 14 to June 14, 2020 were analyzed in detail, focusing on the MS event energy and spatial distribution of the first extremely intense rockburst. In addition, the effects of the daily excavation distance and excavation speed on the characteristics of extremely intense rockburst and MS activity were explored. Finally, the waveform and time–frequency characteristics of rockbursts with different intensities in the different surrounding rock classifications are discussed. According to the characteristics of the time–frequency, the extremely intense rockbursts in the classification I surrounding rock are divided mainly into low-frequency sustained type, low-frequency discontinuity type, and high-frequency discontinuity type, and the extremely intense rockbursts in the classification II surrounding rock are divided mainly into high-frequency discontinuity type and low-frequency discontinuity type. The study results are of great significance for improving the excavation efficiency and rockburst prediction accuracy in deep-buried tunnels with frequent rockbursts.