Numerical analysis of railway transition zones in soft soil

Transition zones are constructions intended to provide smooth passage of a train, when moving from a track supported on an embankment to a track on a stiff structure, such as a bridge, tunnel or culvert. The design of transition zones is based on creating a gradual stiffness variation between the free track and the stiffer structure. In the Netherlands, the standard transition zone design consists of placing a concrete approach slab before and after the structure. In the present paper, the performance of a typical transition zone is assessed, by means of numerical analysis. After validation of the results it is shown that the presence of a concrete slab, combined with the fact that the sleepers are hanging, causes a stress redistribution towards the free end of the approach slabs. This aggravates the long-term deformation of the soil and increases the differential settlement under normal train speed. A critical train speed is identified for the transition zone.