Three-dimensional track-ballast interaction model for the study of a culvert transition

Transition zones corresponding to the passage from railway tracks on embankments to settlement free structures are frequently problematic for maintenance. Changing stiffness of the track and differential settlements are main causes for the degradation of tracks and foundations at transitions. This paper concentrates on a railway passage over a box-culvert, where significant settlements were observed in the transition zones. Previous research using a Winkler type model showed that this cannot be explained by ballast compaction due to trains passage only. The paper presents a 3-D model. It describes the behaviour of the rail track, ballast, embankment and approach slabs. This calculation shows that the stress in the soil close to the approach slabs exceeds the strength of the ballast. This leads to rolling of particles on the approach slab and explains the differences between the Winkler type model results and the observed settlements.