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. There are five main fault types: 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. In pursuit of this objective, this study presents a novel semi-analytical model that accounts for five distinct types of faults and analyzes complex mathematical problems via the finite difference method, thereby circumventing the need to derive intricate analytical solutions. Additionally, an unconventional iterative approach is suggested for the computation of the nonlinear interaction between the tunnel and soil. This method exhibits exceptional efficiency, requiring less than one second per calculation on a laptop. Furthermore, when compared to a numerical model based on finite elements and varying fault displacements, this model demonstrates that the longitudinal forces and displacements are quantitatively in good approval, even when massive fault displacements are considered. Finally, this model is utilized to assess the longitudinal displacements, forces, and safety factors of the Daliang tunnel under faulting, and the failure range and failure modes are consistent with the actual situation. The suggested approach addresses a gap in the existing literature and is valuable for quickly, cost-effectively, and stably analyzing and designing tunnels intersecting with active faults.