Mechanical response of a tunnel subjected to strike-slip faulting processes, based on a multi-scale modeling method

The stick-slip action of strike-slip faults poses a significant threat to the safety and stability of underground structures. In this study, the north-east area of the Longmenshan fault, Sichuan, provides the geological background; the rheological characteristics of the crustal lithosphere and the nonlinear interactions between plates are described by Burger’s viscoelastic constitutive model and the friction constitutive model, respectively. A large-scale global numerical model for plate squeezing analysis is established, and the seemingly periodic stick-slip action of faults at different crust depths is simulated. For a second model at a smaller scale, a local finite element model (sub-model), the time history of displacement at a ground level location on the Longmenshan fault plane in a stick-slip action is considered as the displacement loading. The integration of these models, creating a multi-scale modeling method, is used to evaluate the crack propagation and mechanical response of a tunnel subjected to strike-slip faulting. The determinations of the recurrence interval of stick-slip action and the cracking characteristics of the tunnel are in substantial agreement with the previous field investigation and experimental results, validating the multi-scale modeling method. It can be concluded that, regardless of stratum stiffness, initial cracks first occur at the inverted arch of the tunnel in the footwall, on the squeezed side under strike-slip faulting. The smaller the stratum stiffness is, the smaller the included angle between the crack expansion and longitudinal direction of the tunnel, and the more extensive the crack expansion range. For the tunnel in a high stiffness stratum, both shear and bending failures occur on the lining under strike-slip faulting, while for that in the low stiffness stratum, only bending failure occurs on the lining.