Study on the Deformation Mechanism of Tunnels Crossing Fault Zones and Numerical Simulation of NPR Support

Tunnels crossing fault zones are common in railway engineering, water conservancy engineering and highway engineering. Engineering geological disasters induced by crossing fault fracture zones account for more than 50% of the total number of tunnel disasters in China. Ensuring the safety and stability of tunnels crossing fault zones is the top priority in the development of tunnel engineering in China. Based on the engineering background of Tabaiyi Tunnel, this paper explores the effective support measures of surrounding rock under the influence of fault fracture zone. In order to solve the problem of large deformation of soft rock in Tabaiyi Tunnel, this paper first explores the main controlling factors of large deformation by carrying out on-site point load test, in-situ stress test and indoor mineral composition analysis test. Then, according to the deformation mechanism of Tabaiyi Tunnel, a high pre-tightening force and long-short NPR anchor net support scheme is proposed. According to the excavation compensation theory, the high pre-tightening force of NPR anchor cable is used to compensate the stress of tunnel surrounding rock. Through numerical simulation and field monitoring, it is shown that the tunnel can effectively reduce the large deformation of surrounding rock under the influence of fault fracture zone under the high pre-tightening force and long-short NPR anchor net support scheme. The research results can provide reference for tunnel support crossing fault zone.