Study on anti-dislocation design parameters of tunnel structure with flexible joints crossing fault based on simplified analytical method

The tunnel structure is susceptible to shear failure due to fault dislocation action, particularly in regions with high seismic activity. To mitigate this risk, the use of tunnel segmental lining and flexible joints has been identified as an effective anti-dislocation strategy. However, the design of these components lacks available analytical solutions. To address this gap, a simplified longitudinal beam-spring tunnel model has been developed to assess the longitudinal response of tunnel structures, incorporating the splaying and staggering deformations at flexible joints. The virtual node method is employed to efficiently solve the problem of discontinuous deformation at these joints. An analytical solution for the longitudinal response of tunnels with flexible joints subjected to fault dislocation is derived utilizing the established governing equations, continuity conditions at the flexible joints and boundary conditions. The validity of the proposed solution is confirmed through comparisons with results from model tests and numerical simulations. Subsequently, a sensitivity analysis is conducted to explore the effects of segmental lining length, flexible joint parameters, and fault zone width. The findings reveal that flexible joints significantly enhance the anti-dislocation capability of tunnel structures, reducing the longitudinal strain of tunnel linings by 57.68 %. Furthermore, the anti-dislocation performance can be further improved by decreasing the stiffness of the flexible joints. Notably, the flexible joints located at the interface between the fault zone and the moving or fixed block endure the most shear and rotational deformations. Additionally, a negative correlation is observed between the required width of flexible joints and the length of segmental lining.