Scientific design of a railway track formation requires an understanding of the subgrade behavior and the factors affecting it. These include the effective resilient stiffness during train passage, which is likely to depend on the stress history and the stress state of the ground, and the stress path followed during loading. This study investigates the last of these, by means of a two-dimensional dynamic finite-element analysis. The effects of train speed, acceleration/braking, geometric variation in rail head level, and a single unsupported sleeper are considered. Results indicate that dynamic effects start to become apparent when the train speed is greater than 10% of the Rayleigh wave speed, vc , of the subgrade. At a train speed of 0.5 vc , the shear stresses will be underestimated by 30% in a static analysis, and at train speeds greater than vc the stresses due to dynamic effects increase dramatically. Train acceleration/braking may increase shear stresses and horizontal displacements in the soil, an...

Transition zones between railway tracks on embankments or natural ground, and fixed substructures such as bridges and culverts, typically require extensive maintenance to retain acceptable track geometry. These high maintenance costs and the potential to cause delays to train services are of major concern for railway infrastructure managers. In view of the importance of the problem, surprisingly little research has been carried out to identify the fundamental causes of the poor performance of transition zones. To better understand the physical mechanisms involved, an extensive monitoring and investigation programme was undertaken on a typical transition zone in the Netherlands, comprising reinforced concrete approach slabs linking the normal track onto a concrete culvert. Accelerations and velocities of the track, soil, and approach slabs in response to passenger trains were measured, from which displacements were calculated. In addition, track settlements and pore water pressures were monitored over a 1-year period. This article presents and discusses the measurements made. The results highlight the problems associated with track quality at a transition zone, including the large dynamic displacements induced during train passage and the tendency for ongoing long-term movement. The implications of these for design and maintenance are discussed.

Summary. Compressional wave (P wave) and shear wave (S wave) velocities (Vp and Vs, respectively) from remote seismic methods have been used to infer the distr