Study on the support strategy of excavation compensation structures based on dual-gradient grouting in cross-fault zone tunnels

The conventional Mine Tunneling Method (MTM) and the New Austrian Tunneling Method (NATM) are not sufficient to cope with the excavation and support of deep through-fault fracture zone tunnels with significant asymmetric large deformations. Therefore, new over-reinforcement materials and steel structures are needed to effectively deal with this complex situation. In this study, the coupling technique of dual-gradient grouting (DGG) and negative Poisson’s ratio (NPR) anchor cable structure is adopted. Through mechanical modeling, numerical simulation and on-site monitoring, the support problem of large deformation soft rock tunnels traversing multi-phase fracture and fragmentation zones is studied for the first time. The results show that the support technology of “dual-gradient grouting + NPR anchors,” which combines pre-consolidation with rapid and timely flexible control, has significant mechanical compensation effect on the deformed surrounding rock of tunnels through fault zones. This method effectively controls the tunnel deformation below 278 mm and maintains a constant resistance value of about 350 kN. This study provides a scientific basis for supporting other large deformation soft rock tunnels across multilevel fault fracture zones.