Mechanisms and mitigation effects of oblique seam linings in fault-crossing tunnels: combined experimental and numerical evidence under normal faulting

Abstract

To evaluate the influence of sectional seam configurations (normal vs. oblique) on the fault-crossing performance of tunnels, this study integrates 1:40 scale model tests with three-dimensional elasto-plastic finite element simulations. The mechanical behavior and damage mechanisms of tunnels subjected to normal fault dislocation were comprehensively examined through deformation patterns, contact earth pressure, strain distribution, internal force characteristics, and failure modes. Experimental results indicate that tunnels with normal seams undergo severe longitudinal tensile-flexural failure and shear-induced spalling near the fault rupture surface, accompanied by dense cracking. In contrast, oblique seam tunnels demonstrate enhanced structural flexibility, reduced crack density, and absence of large-scale spalling, reflecting improved adaptability to fault displacement. Peak longitudinal strain was reduced by up to 80% at the crown exterior and 13% at the invert exterior, while earth pressure at the crown and invert decreased by 70 and 20%, respectively. To validate these findings, numerical simulations employing the concrete damaged plasticity (CDP) model were conducted. The results exhibited consistent damage evolution trends, with oblique seams effectively redistributing tensile stress and mitigating compressive damage. Furthermore, global damage indices quantitatively confirmed the superior fortification performance of oblique seam linings. This integrated experimental–numerical approach offers robust evidence and a scientific basis for the seismic design and resilience enhancement of tunnels intersecting normal faults.