A Semi-Analytical Method for Stress-Strain Analysis of Tunnels under Dip-Slip Faulting Based on an Elastic-Plastic Foundation Beam Model

Tunnels under faulting will be seriously damaged, and an accurate analytical method is an effective tool for tunnel response assessment in preliminary design. A series of mechanical analytical methods have been developed for tunnels under faulting. However, some unrealistic assumptions are still employed in the analytical method for tunnels under dip-slip faulting, including tunnel segmentation, constant stratum stress, and axial force in governing equations of tunnel displacement, which increases the solution complexity and decreases the accuracy. In this paper, a tunnel crossing an active fault is simplified as a large deformed continuous beam acting on an elastic-plastic foundation, and the tunnel-stratum interaction is treated as a series of axial and vertical elastic-plastic springs; the elastic-plastic tunnel-stratum interaction stresses and axial force are considered in the governing equations by using the finite difference method and a novel iterative method. In this way, the three assumptions employed in the existing analytical methods are removed. Later, the proposed method is verified by comparing it with the results from the model test, numerical simulation, and existing method. The comparisons show that the results of the proposed method agree excellently with those from the model test and numerical model, and the accuracy is higher than that of the existing analytical method. Finally, the failure scope and stress distribution of tunnels under the action of normal and reverse faulting are analyzed in detail.