Subway tunnels with rectangular cross-sections in soil layers are susceptible to damage from fault dislocations, particularly when multiple faults are involved. The interaction between tunnel structures and multiple fault displacements can lead to significant stress and cumulative damage. The focus of this study is to investigate the mechanical behavior of a rectangular subway tunnel under the influence of multiple normal fault dislocations using validated numerical simulations. By analyzing the cumulative damage effects and the impact range from these fault displacements, the study proposes defense strategies and mitigation measures to enhance tunnel safety. The results show that tension damage occurs at the tunnel crown in the footwall and the invert in the hanging wall, and tension-bending-shear damage was observed at the tunnel sidewalls at the fault. Compared to horseshoe-shaped tunnels, rectangular tunnels exhibit a more uneven stress distribution across section, with tensile stress up to 5 times higher. Simultaneous displacements of multiple faults result in high tensile stress, especially at the crown and invert, while sequential fault dislocations cause progressive damage in these areas, shifting the stress to the sidewalls with a 50% reduction. The cumulative plastic strain from sequential displacements is three times greater than that from simultaneous displacements. In areas with closely spaced faults, overlapping damage zones can occur. To mitigate these effects, anti-fault measures such as deformation joints and enlarged tunnel cross-sections are recommended, along with enhanced waterproofing solutions, including waterstop strips and embedded grouting pipes. These findings offer valuable insights into ensuring the safety of tunnels in fault-prone regions and provide practical strategies for mitigating fault-induced damage.

Bedrock fault dislocation is a crucial structural factor influencing landslide movement. Accurately predicting the location and scale of rupture zones within a slope body is essential for effective slope construction design and risk mitigation. Based on an analysis of seismic damage in slope cross-bedrock faults, this article creatively realizes the physical model test of the slope and its covering layer site with soil rupture zones at the top and toe of the slope caused by the dislocation of the bedrock normal fault. Through the model test, macroscopic phenomena were observed, and microscopic analysis was obtained by deploying sensors. The main results were as follows: (i) The evolutionary process of the instability mechanism could be divided into three stages: crack damage stage (Stage I), crack expansion and penetration stage (Stage II), and slope instability stage (Stage III). (ii) Two rupture modes of the soil body in the slope under bedrock dislocation were identified, with the rupture mode at the slope crest having a greater impact on the soil slope. (iii) Inferring the position of bedrock faults through the location of the main rupture zones on the slope surface represents a feasible supplementary method for identifying seismogenic structures during field surveys. These research results provide a scientific basis for the stability assessment of cross-fault slopes and the reinforcement design of landslide disasters.

Taking the tunnels crossing active faults in China's Sichuan-Tibet Railway as the research background, experimental studies were conducted using a custom-developed split model box. The research focused on the cracking characteristics of the surrounding rock surface under the action of strike-slip faults, the progressive failure process of the tunnel model, and the mechanical response of the tunnel lining. In-depth analyses were performed on the tunnel damage mechanism under strike-slip fault action and the mitigation effects of combined anti-dislocation measures. The results indicate the following: Damage to the upper surface of the surrounding rock primarily occurs within the fault fracture zone. The split model box enables the graded transfer of fault displacement within this zone, improving the boundary conditions for the model test. Under a 50 mm fault displacement, the continuous tunnel experiences severe damage, leading to a complete loss of function. The damage is mainly characterized by circumferential shear and is concentrated within the fault fracture zone. The zone 20 cm to 30 cm on both sides of the fault plane is the primary area influenced by tunnel forces. The force distribution on the left and right sidewalls of the lining exhibits an anti-symmetric pattern across the fault plane. The left side wall is extruded by surrounding rock in the moving block, while the right side wall experiences extrusion from the surrounding rock in the fracture zone, and there is a phenomenon of dehollowing and loosening of the surrounding rock on both sides of the fault plane; the combination of anti-dislocation measures significantly enhances the tunnel's stress state, reducing peak axial strain by 93% compared to a continuous tunnel. Furthermore, the extent and severity of tunnel damage are greatly diminished. The primary cause of lining segment damage is circumferential stress, with the main damage characterized by tensile cracking on both the inner and outer surfaces of the lining along the tunnel's axial direction.

The fault dislocation produces severe additional deformation on cross-fault tunnels along the axial direction, seriously threatens tunnel safety. To this end, a simplified analytical model for evaluating the mechanical behavior of segmental tunnels subjected to buried fault dislocation was established. The segmental tunnel is treated as a Timoshenko beam acting on the Vlasov elastic foundation. The plastic yield of circumferential joints, the effect of frictional resistance along the axial direction, and the deformation characteristics of overburden soil after faulting were considered. Then, the reasonability of the analytical solution is proved by 3D numerical simulation. The tunnel safety state was evaluated based on the joint deformation of the segmental tunnel. Subsequently, the effects of plastic yield behavior between segmental rings, plastic equivalent bending stiffness ratio, segment dimensions, and longitudinal bolt on the longitudinal response of the segmental tunnel linings were investigated. The results show that the simplified analytical solution proposed is reasonable in predicting the joint deformation between segmental rings when the segmental tunnel is subjected to buried fault dislocation. When the normal faulting is imposed, the segmental tunnel is dominated by tensile deformation along the tunnel axial. Under 20 cm of normal faulting, the joint opening between segmental rings is close to the deformation control value of joint waterproofing. However, the shear deformation has been significantly weakened due to the effect of faulting in the propagation process to the surface. The calculation result is too small when the plastic deformation behavior is ignored. The plastic equivalent bending stiffness ratio eta 2 inversely correlated with the maximum joint opening. Increasing the strength grade or the number of longitudinal bolts has a relatively limited effect on reducing the opening between segment rings, where the joint still has a greater risk of water leakage.