The dislocation of the active fault zone altered the stress distribution and geometry of the track structure in the tunnel, which in turn affected the safety and stability of the train operation. Polyurethane-solidified track bed (PSTB) is suitable for sections crossing through active fault zones due to its excellent serviceability and adaptability to deformation. In this study, the stress and deformation response induced by active fault dislocation are investigated for this novel track structure. The corresponding deformation of track structure is subsequently introduced into a vehicle-track dynamics model to calculate the train operation safety index. The study examines the impact of fault displacement on railway track structures, revealing significant vertical deformation in rails that corresponds to the displacement magnitude. The effects are mainly confined to the active fault zone and its immediate surroundings, with variations depending on the fault zone’s structural characteristics. Key factors such as larger displacements, steeper fault angles, and narrower fault zones increase stress on track components, particularly the wide sleeper, which is prone to cracking and represents a structural vulnerability. Higher fault displacement, narrower zones, steeper angles, and increased train speeds elevate derailment risks and wheel load reduction rates, potentially exceeding safety limits. To ensure safety under typical fault conditions, train speeds should not exceed 250 km/h for PSTB with a 40 mm displacement and a 60° fault angle. These findings provide critical guidance for railway construction in fault-prone areas.

This study investigates the dynamic response and local stability of gravity-anchored foundations constructed in layered argillaceous sandstone under the coupled effects of wet–dry cycling degradation and cyclic vehicle loads. Based on in situ direct shear tests and FLAC3D 7.0 numerical simulations, a concrete–rock interface model, a rock mass direct shear model, and a three-dimensional dynamic model of the anchored foundation were developed. The parameters of the interface model were validated using the results of the direct shear tests. Wet–dry cycling degradation was subsequently incorporated to analyze the cyclic shear response of the interface and rock mass under different numbers of cycles. Cyclic vehicle loads were modeled as increments in main cable tension with an equivalent sinusoidal waveform. The results indicate that as the number of wet–dry cycles increases, the cyclic shear hysteresis loops shift overall toward lower shear stress levels. Peak shear stress decreases by approximately 49.26–51.64% compared to the natural state, and the hysteresis loop area decreases significantly. This indicates that wet–dry cyclic degradation weakens the cyclic shear resistance and energy dissipation capacity of the contact surface and rock structural planes. Dynamic analysis results for the anchor foundation indicate that wet–dry cycling degradation significantly increases the displacement response levels of the rock mass near the front toe and rear heel. Specifically, under the n = 20 condition, the displacement at the last peak increased by approximately 109.3–123.9% compared to the undisturbed state; simultaneously, the local plastic zones in the rock mass surrounding the anchorages gradually expanded, and the local safety factors of the rock mass near the toe and heel decreased overall. This study elucidates the degradation mechanisms and dynamic behavior of gravity anchors under the combined action of environmental and operational loads, providing a basis for the design and safety assessment of foundations for long-span suspension bridges.

Polyurethane-solidified ballast (PSB) technology and geogrid reinforcement can be used to strengthen ballast beds. However, there has been little research on the mechanical properties of ballast beds under the combined effects of these two methods. This study addresses this research gap through an integrated experimental–numerical investigation of the cooperative reinforcement mechanisms. Uniaxial compression and oblique shear tests were conducted on standard and geogrid-reinforced PSB specimens, and a three-dimensional random aggregate finite element model was developed to represent the actual ballast gradation. The results show that geogrid reinforcement increased the compressive strength by 42.1% and reduced the maximum lateral deformation by 14.2%, while having little influence on the elastic modulus and Poisson’s ratio. In the oblique shear tests, geogrid reinforcement increased the peak loads by 14.2–23.0% compared with the standard specimen. A directional dependence was also observed, with the highest peak load occurring when the shear plane corresponded to the unreinforced surface. These findings clarify the cooperative reinforcement mechanism between polyurethane solidification and geogrid confinement and provide a mechanical basis for designing reinforced ballasted trackbeds in heavy-haul railways subjected to high axle loads and pronounced lateral deformation, as well as in high-speed railway lines requiring enhanced track stability.