Study on the tunneling response of TBM in stressed granite rock mass in Yinhan Water Conveyance tunnel

The initial stress of the surrounding rock mass will be redistributed during TBM tunneling in a deep tunnel. This process may induce brittle failure of the surrounding rock mass, which has a great impact on TBM construction. The southern section of the Yinhan Water Conveyance Tunnel is mainly composed of massive to intact granite, with a maximum overburden depth of nearly 2000 m. The paper discussed in detail the relationship between various brittle failure degrees at the typical tunnel faces and TBM performance. The typical patterns, such as undamaged, slabbing, and strain rockburst at the tunnel face, and the corresponding characteristics of the TBM performance parameters were revealed. As the severity of damage increases, the rock mass boreability is improved, the cutterhead thrust is reduced, and the penetration increases, but there is an upper limit. It is noteworthy that the field penetration index (FPI) fluctuation expressed by the coefficient of variation (CV) varies significantly in different stress states. Based on the excavation response of TBM, a Rockburst Warning Index (RWI) was proposed to assess the brittle failure degree of the excavated rock mass in real-time. The results of the study can provide some insights into the prediction of TBM performance and the early warning of rockburst in deep-buried hard rock grounds.