A Novel Semi-Analytical Method for Longitudinal Mechanical Analysis of Tunnels Crossing Active Faults

Tunnels that cross active faults will inevitably be severely damaged. And there are mainly five fault types, i.e., strike-slip fault, normal fault, reverse fault and oblique-slip fault (normal or reverse strike-slip fault). However, there is no calculation method of tunnel longitudinal mechanical analysis for all fault types, and the calculation accuracy is reduced by the assumptions used in the existing calculation models to simplify the solution of complex differential equations. To this end, a novel semi-analytical model is proposed in this work, which considers five kinds of faults and uses finite difference method to solve the complex differential equations, avoiding the derivation of complicated analytical solutions. And a novel iterative method is proposed to calculate the nonlinear interaction between soil and tunnel, which is highly efficient and taking less than a second per calculation on a laptop. Additionally, this model is compared with a finite element-based numerical model with various fault displacements, and the longitudinal forces and displacements are in excellent quantitative agreement, even for cases of large fault displacement. Finally, this model is employed to evaluate the longitudinal displacements, forces and safety factors of Daliang tunnel under faulting, and the failure range and failure modes are consistent with the actual situation. The proposed method fulfills the missed part of literature, and it is valuable for fast, economic, and reliable analysis and design of tunnels crossing active faults.