Effects of fault slip surfaces and fractured zones on the mechanical response of track structures

Fault displacement induces deformation and concrete damage in track structures of cross-fault tunnels, threatening tunnel–track operational safety. Unlike conventional studies assuming fault displacement occurs along the central plane of a single fracture zone, this study investigates the effects of sliding surface location and fracture zone width on the mechanical responses of double-block ballastless tracks under quasi-static fault displacement. Based on the concrete damaged plasticity (CDP) theory and the cohesive zone model (CZM), a three-dimensional surrounding rock–tunnel–track model was established. Fault displacement was simulated using prescribed displacements, and parametric analyses were conducted for different sliding surface locations and fracture zone widths. The results show significant differences in track deformation, damage, and interlayer contact. Case S3 generally exhibits the highest damage variable, while the total damaged volume and severely damaged volume show different trends. The interlayer gap and cohesive damage area increase from S1 to S3. Increasing fracture zone width smooths the deformation curve and alleviates plastic damage. At a fault displacement of 20 mm, the maximum damage variable decreases from 0.613 to 0.499 as the fracture zone width increases from 15 m to 75 m. These findings provide a basis for ballastless track design in cross-fault tunnels.