Study of the failure characteristics and mechanical response of railway tunnel under oblique-slip fault displacement

When a tunnel intersects an active fault, the dislocation of the fault often leads to failures such as lining fractures and structural deformations, severely threatening the safe operation of the tunnel. To investigate the fracture characteristics and mechanical responses of tunnels under oblique-slip fault conditions, a large-scale indoor model test with a geometric similarity ratio of 1:35 was conducted. This study was based on a railway tunnel in Western China that crosses an oblique-slip active fault. Additionally, a three-dimensional model of the tunnelsurrounding rock-fault fracture zone interaction was established using ABAQUS finite element analysis software. The purpose of this study is to clarify the structural cracking characteristics, deformation modes, strain trends, changes in bending moment and shear force of tunnels under fault displacement, as well as the contact force between tunnels and surrounding rocks, and further reveal the differences in the impact of oblique-slip faults and other types of faults on tunnels. The results indicate that under oblique-slip fault dislocation, the tunnel experiences shear failure at the fault fracture zone manifested as shear diagonal cracks. Tensile bending failures, characterized by bending circumferential cracks, occur at the hanging wall and footwall. At the fault fracture zone, the strain, contact pressure, bending moment, and shear force of the tunnel undergo drastic changes and peak values appear. The tunnel exhibits distinct three-dimensional failure characteristics, including horizontal bending, axial stretching and twisting, and vertical shearing. The damage zone of the tunnel extends approximately 2D (where D is the tunnel diameter) from both the hanging wall and footwall towards the fault fracture zone, with the severity of damage increasing closer to the fault fracture zone. The damage process of the tunnel under increasing fault dislocation displacement can be divided into three stages: initial intact stage, onset of damage stage, and complete failure stage. When the strike-slip dislocation reaches 20.7 mm (corresponding to an actual displacement of 724.5 mm), structural damage accumulates to its limit, leading to large-scale failure of the tunnel. Compared to purely strike-slip faults, the tunnel is more prone to damage and exhibits a larger range of structural failure under oblique-slip fault dislocation. These findings provide scientific and rational data support and reference for disaster prevention and mitigation design of tunnels.