Failure characteristics and development mechanism of fault rockburst in a deep TBM tunnel: a case study

An intense fault rockburst recently occurred in a deep tunnel excavated by tunnel boring machine in China, which was taken as a case to study the failure characteristics in detail. The temporal and spatial evolution of microseismic (MS) activity, the dynamic stress drop and the spatial distribution characteristics of rock fracture mechanism were analyzed. Stress-induced mechanism was studied using numerical simulation, and the development mechanism of the fault rockburst was revealed finally. The research results are as follows: (1) The development process of the fault rockburst is divided into six stages: calm stage, crack initiation stage, crack development stage, crack accumulation–slight fault dislocation stage, further crack accumulation stage and crack penetration–fault slip stage. (2) During the development of the fault rockburst, stress and energy accumulate in the deep of surrounding rock. When rockburst occurs, stress and energy are released in the shallow of the surrounding rock; at the same time, the dynamic stress drop increases significantly. MS energy is released intermittently during the development of fault rockburst. (3) Affected by the geological condition, the high in situ stress and the excavation unloading, horizontal shear slipping of the fault occurs, leading to fault rockburst. These research results can provide a reference for establishing the warning and mitigation methods of fault rockburst in deep TBM tunnels.