Research on energy-absorption active control method for large deformation of tunnel surrounding rock through multi-fault fracture zone

To study the problems of large deformation of surrounding rock and water-rich dense fracture zones during tunnel construction through fault fracture zone, the NPR (Negative Poisson’s Ratio) anchor cable control method is studied based on the Tabaiyi Tunnel. First, the mechanical deformation mechanism of surrounding rock is analyzed by geological conditions, lithology and strength of surrounding rock, and different surrounding rock zones are obtained. Then, based on the self-developed high-prestressed NPR anchor cable, the tunnel prevention and control measures are designed. The high-stress NPR anchor net technology is used to support the common large deformation and fault fracture zone, while in the water-rich dense fracture zones, the combined support of double gradient grouting technology and high-stress NPR anchor net technology is adopted. Finally, to evaluate the control effect of the support design scheme, the deformation of surrounding rock, the axial force of NPR anchor cable, and the pressure of steel arch are monitored in real time. The results show that the high-stress NPR anchor net technology can effectively control the large deformation of tunnel surrounding rock caused by fault zone. In addition, in the water-rich zones, the double gradient grouting technology can provide sufficient anchoring force for the NPR anchor cable. The two technologies control the maximum deformation of surrounding rock within 300 mm and realize the stability of tunnel primary support.