Prediction of track settlement at high-speed railway transitions between embankment and bridge in the proximity of a turnout

Abstract

It is well known that transition zones are subject to high differential settlement rates mainly due to the rapid change in track system stiffness as well as materials used. This problem is even more notable in high-speed lines where the dynamic effects are critical. In this paper, a methodology that combines large FE track models and vehicle-track MBS software with relatively low computational costs is proposed to calculate the long-term track behaviour in transition areas. The substructure dynamic characteristics are captured using an equivalent Lump Parameter (LP) model whose parameters are tuned against the FE track model to correctly reproduce the frequency response of the full track. The dynamic behaviour of the whole system is predicted using the in-house vertical vehicle-track software RailDyn. A settlement algorithm accounting for the development of hanging sleepers is then used in iterative simulations. A typical European high-speed transition zone between embankment and bridge is considered as a case study and various scenarios are analysed, including when a switch is located in proximity. Results show that the cement-bound reinforced and layered design considered creates a smooth increase of stiffness through the transition. On the other hand, localised differential settlement is predicted at the position of change in track stiffness, leading to an increase of stress in the ballast layer and a decrease in the layers beneath. The long-term soil behaviour at the switch panel is found to be completely dissociated from the behaviour at the transition when located at or more than 25 m from the bridge, as is the current practice.