Model Test Study on Deformation and Failure of Metro Shield Tunnel under Normal Faulting

To reveal the deformation and failure characteristics of the metro shield tunnel overpassing buried fault, a self-designed loading test device for faulting simulation was used to carry out a 1∶25 geometric scale cross-fault shield tunnel model test. The mechanical response law and deformation failure characteristics of the shield tunnel under normal faulting were analyzed. The test results show that under 2 cm normal faulting, the longitudinal differential deformation of the tunnel shows a nonlinear increasing trend. The opening of the circumferential joint is mainly located at the vault of the footwall tunnel. The arch bottom of the hanging wall tunnel and the peak opening of the circumferential joints have exceeded the waterproof limit of the joints. The diameter convergence deformation of the segment lining at the junction of the fault extension line and the tunnel occurs severely. The stress state of the outer side of the arch waist of the tunnel lining is tensioned, while the outer side of the vault and the arch waist are compressed. The contact pressure between the tunnel and the stratum is greatly affected by the faulting, and there are surrounding rock compression and loosening zones. However, the peak value of contact pressure is relatively limited. Tensile fracture of the circumferential joint, longitudinal cracking of the segment, and joint deformation are the main deformation and failure characteristics of the shield tunnel. The probability of oblique shear failure and local crushing failure is low. Based on the longitudinal deformation and failure characteristics of shield tunnels, the joints deformation and the tensile fracture of the circumferential joint should be taken as the main control indexes to define the structural failure of cross-fault shield tunnels. Based on the deformation and failure characteristics of segmental lining, suggestions on structural design and countermeasures of cross-fault shield tunnel are proposed. © 2024 Hunan University. All rights reserved.