Three-Dimensional Dynamic Finite Element Modeling of Transition Zones in Ballasted High-Speed Tracks.

Transition zones in railway tracks, where vertical stiffness changes abruptly such as between ballasted tracks and rigid structures like culverts or bridges, pose significant challenges in high-speed rail lines. These abrupt stiffness variations can result in increased track deterioration, differential settlement, and elevated maintenance costs due to dynamic load impacts. This study presents a comprehensive three-dimensional (3D) dynamic finite element model, using PLAXIS 3D, to analyze the behavior of transition zones by focusing on a culvert-open track interface under high-speed train loading conditions. The model was validated against published numerical results and applied to assess the influence of key parameters: direction of train movement, backfill soil type, and embankment height. Results reveal that the direction of train movement significantly affects vertical rail displacement with higher displacements observed when moving from embankment to culvert. The stiffness and strength of the backfill soil greatly influence track response, where improved soil conditions reduce vertical displacement by up to 60%. Furthermore, increasing the embankment height over the culvert leads to a substantial reduction, by up to 97%, in displacement differences between stiff and soft sections highlighting its effectiveness as a mitigation technique. This work provides critical insights into the dynamic behavior of transition zones in ballasted tracks and offers design guidance for improving track performance and longevity in high-speed rail systems.