Keywords: transition zone, finite element, empirical settlement model, settlement, railway.

Transition zones in railway tracks are locations with considerable changes in the vertical rail support. Typically they are located near engineering structures, such as bridges, culverts, tunnels and level crossings. In such locations, the variation of the vertical stiffness together with the differential settlement of the track (when the foundation settles unevenly) on both sides of the transition result in amplification of the dynamic forces acting on the track. This amplification contributes to the degradation process of ballast and subgrade, ultimately resulting in deterioration of the vertical track geometry, which in turn causes further amplification of the dynamic forces to the track.

To predict the permanent settlement of the track transition zones, a combination of the finite element model and empirical settlement models has been proposed. The finite element model is a three-dimensional dynamic model (explicit integration) of a track transition zone, with a vehicle, two ballast tracks and a section of bridge in between. The empirical settlement models indicate the relationship between the stress of ballast and growth of the permanent settlement. To demonstrate the method, the iterative procedure is presented for the first time and the settlements of the compacted ballast after 10000 cycles of the track at locations close to the transition zone have been predicted. In addition, the distribution of ballast stress and the difference between two empirical settlement models are analysed.

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