Microseismic Energy and Intensity Criterion of Rockburst in Deep TBM Tunnels:A Case Study of the Neelum-Jhelum Hydropower Project

Rockburst hazards caused by excavation in deep tunnel boring machine(TBM)tunnels endanger construction safety.Based on 43 rockburst events and related microseismic(MS)energies in the deep TBM tunnels in the Neelum-Jhelum hydropower station in Pakistan,the MS energy characteristics and intensity identification of rockburst events in deep TBM tunnels were studied.The rockburst event was preprocossed using distance discrimination method for case expansion,and the characteristics of MS energies of rockburst events with different intensities and lithological conditions in TBM tunnel were investigated.Using the quantitative parameter of MS energy,a criterion for identifying the rockburst intensity in deep TBM tunnels under different conditions was established.The higher the rockburst intensity,the greater the quantitative threshold of MS energy,and the two show a nonlinear relationship.The threshold value of MS energy for sandstone is greater than that of siltstone for the same intensity of rockburst.It is necessary to differentiate the lithology when identifying the intensity of rockburst events.The established criterion was validated in the project,and the results show that the established criterion is reliable.The results can provide a basis for understanding rockburst events and provide advance warning thereof in deep TBM tunnels.