Study on Warning Method for Fault Rockburst in Deep TBM Tunnels

Fault rockburst warning has always been challenging in deep tunnel engineering, and there is no quantitative warning method for deep tunnel boring machine (TBM) tunnels. This study clarified the geological characteristics and microseismic (MS) activity characteristics of fault rockbursts, and a quantitative warning method that integrates geological information and MS information was established. The results of this study show that fault rockbursts are prone to occur near faults without filling or with hard filling, where the faults run through the tunnel, and where the orientation of the fault is at a small angle to the direction of the maximum principal stress. Fault rockbursts exhibit significant precursor characteristics during the development process, that is, MS events are characterized by a significant distribution along faults, a cumulative apparent volume growth rate of adjacent MS events greater than 45%, and an overall rising trend in the ratio of cumulative apparent stress to cumulative dynamic stress drop (K value), which can be used to identify whether a potential rockburst will be a fault rockburst. To further predict fault rockbursts, seven MS parameters were comprehensively used, including the intraday and cumulative number of MS events, intraday and cumulative MS release energy, intraday and cumulative MS apparent volumes, and K value. Based on the CRITIC method for determining weight coefficients, a quantitative fault rockburst warning method was established and successfully applied to a deep TBM tunnel. This method achieves dynamic warning of type identification, intensity, and probabilities of fault rockbursts during the excavation process of deep TBM tunnels.HighlightsFault rockbursts are prone to occur near faults without filling or with hard filling, where the faults run through the tunnel, and that the fault orientation is at a small angle to the maximum principal stress.Fault rockbursts have significant precursor characteristics: MS events are characterized by a significant distribution along the faults, a cumulative apparent volume growth rate (CAVG) of adjacent MS events greater than 45%, and an overall rising trend in the ratio of cumulative apparent stress to cumulative dynamic stress drop ( value).The value can be used to differentiate the intensities of rockbursts on the basis of characterizing the development process of fault rockburst.A quantitative fault rockburst warning method for deep TBM tunnels was established, which achieves dynamic warning of type identification, intensity, and probabilities of fault rockbursts during the excavation process of deep TBM tunnels.