Keywords: railway track, ballast, track transition zone, video gauge system tests, finite element method.

Transition zones in railway tracks are locations with discontinuity in the vertical support, such as the ones at bridges, culverts and tunnels. In such locations, the vertical support of structures is varying, which causes discontinuity of stiffness, different settlement paces and different velocity of wave propagation. These changes will cause geometry difference in the transition zone, and consequentially increase of the dynamic forces. This can result in damages, especially in the ballast as this is one of the most vulnerable components of track structure. To solve the problems of railway transition zones, the dynamic behaviour of the ballast in the transition zones and the mechanism of track transition degradation should be analysed. Therefore, a series of measurements were performed in a transition area in the Netherlands and a 3D finite element model was developed. The model consists of one section of ballast track and one section of slab track that is stiffer in the vertical direction. The model uses solid elements with an exception of fasteners and rails that are modelled by spring and beam elements respectively. The vehicle is composed by one body, two bogies and four wheels; connected by suspensions, which are simulated by spring elements. To get better understanding of the different phenomena in transition zones, simulations have been performed in different directions, namely, from the ballast track to the slab track and from the slab track to the ballast track. The contact forces of wheel/rail interaction, ballast equivalent stresses and vertical displacements of ballast are analysed and the results are presented and discussed.

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