Hinged design for resisting shear displacement of a deep-buried tunnel crossing an active fault under high in-situ stress conditions

When movement occurs in active faults, tunnels crossing these faults may sustain varying degrees of damage. Most previous studies failed to consider the impact of tunnel depth and high in-situ stress on tunnels crossing active faults, resulting in findings that are not entirely practical. In this paper, the necessity of solving the anti-dislocation problem of deeply buried tunnels is systematically discussed. Through model tests of tunnels crossing active faults, the differences in failures between deeply buried and shallowly buried tunnels were compared. Additionally, a dislocation test of deeply buried segmented tunnels was conducted to analyze the external stress changes, lining strains, and failure modes of the tunnels. The results are as follows: (1) The overall deformation of both deeply and shallowly buried tunnels exhibits an S-shaped pattern. The most severe damage is concentrated in the fault zone. The failure mode of deeply buried tunnels is primarily characterized by shear and tensile failure, resulting in significant compressive deformation and a larger damaged area. In contrast, shallowly buried tunnels mainly experience shear failure, with the tunnel being sheared apart at the fault crossing. (2) After implementing the hinged design for the deeply buried tunnel, the S-shaped deformation pattern is transformed into a ladder pattern, reducing the strain on the tunnel and the peak stress of the external rock mass, thereby significantly mitigating damages. (3) Through the analysis of the distribution of cracks in the tunnel lining, it is found that the tunnel without a hinged design has suffered from penetrating failure, with cracks affecting the entire lining. The cracks in the hinged tunnel affect approximately 66.6% of the total tunnel length, while those in the tunnel with shorter hinged segments affect only about 33.3% of the total length. Therefore, a deeply buried tunnel with shorter hinged segments can yield a better anti-dislocation effect. (4) By comparing previous studies on shallowly buried hinged tunnels, it is concluded that shallowly buried hinged tunnels will also suffer from deformation outside the fault zone, while the damages to the deeply buried hinged tunnel are concentrated mainly in the fault zone. Therefore, the anti-dislocation protection measures for deeply buried tunnels should be concentrated mainly in the fault zone. These findings can provide theoretical guidance and technical support for the design and reinforcement of tunnels crossing active faults under high stress conditions. © 2024 Biodiversity Research Center Academia Sinica. All rights reserved.