Study on the Support Strategy of NPR Cable Truss Structure in Large Deformation Soft Rock Tunnel Across Multistage Faults

The traditional new Austrian tunneling method (NATM) is inadequate for handling the excavation and support of deep soft-rock tunnels with significant deformation. Therefore, new steel structures and materials are needed to effectively manage such complex conditions. This study utilizes the coupling technology of negative Poisson’s ratio (NPR) anchor cable structures and double-layer three-dimensional truss structures, as proposed by Academician He Manchao. Mechanical models, numerical simulations, and field monitoring were employed to investigate the support of large deformation soft-rock tunnels traversing multi-stage fault-fracture zones for the first time. The findings indicate that the support technology combining the flexible control and rigid constraint of “NPR anchor cable + double-layer three-dimensional truss” demonstrates remarkable mechanical compensation for large deformation in soft-rock tunnels. This approach effectively controls tunnel deformation to below 300 mm and maintains a constant resistance value around 350kN. This research provides a scientific basis for supporting other large-deformation soft-rock tunnels across multi-stage fault-fracture zones. Highlights A comprehensive study of soft-rock large deformation tunnels across multi-stage faults has been carried out through numerical simulations, field monitoring and physical modeling tests. The first experimental study of stress compensation in soft-rock large deformation tunnels across multi-stage faults First coupling application of NPR anchor cables with negative Poisson’s ratio effect structures to truss structures