Characteristic microseismicity during the development process of intermittent rockburst in a deep railway tunnel

During deep tunnel excavation, more than one rockburst sometimes occur in a particular area which seriously threatens construction safety. In this work, the characteristic microseismicity occurring during the development process of intermittent rockburst (more than one rockburst occurring in a particular area) and single rockburst (only one rockburst occurring in a particular area) and the associated mechanism of formation are studied. Data was collected during the construction of a railway tunnel in southwestern China. Microseismicity was recorded and analyzed before and after each rockburst (for both intermittent and single rockbursts). The Schmidt number declines heavily with time, the cumulative apparent volume rises sharply with time, and the Seismic activity is high before the rockburst. However, this characteristic microseismicity can also be found with no rockburst occurrence. Between each rockburst in an intermittent rockburst, the MS events mostly have low MS energy, i.e. whose logarithm (measured in Joules) is smaller than 3.5, and the energy stored in the rockmass of the rockburst zone is not adequately released. Therefore, there is likely to be another rockburst after the blast when high in situ stress is present. After the last rockburst of an intermittent rockburst and the single rockburst, some MS events of high MS energy, i.e. whose logarithm (measured in Joules) is larger than 3.5, occur in the deep surrounding rockmass and the energy stored in the rockmass of the rockburst zone is gradually released to a certain degree. The stress is transferred to the deep surrounding rockmass whose stability is relatively high. As a result, a subsequent rockburst is hardly likely to occur again.