Coupled DEM/FDM to evaluate track transition stiffness under different countermeasures

Abstract

Transition zones are vulnerable areas in railway lines, which usually need frequent extra maintenances. Thus, various countermeasures have been proposed to reduce the sudden change of track stiffness in transition zones. However, most of earlier studies applied continuum-based numerical methods (e.g. finite element method, ANSYS) to study the track stiffness problem, ignoring the randomness of ballast layer stiffness, for which effects of different countermeasures on reducing the stiffness difference in transition zone have not been fully revealed. In this paper, a model that combines the discrete element method (DEM) and the finite difference method (FDM) is utilised to evaluate the countermeasures for mitigating track stiffness difference in transition zones. The countermeasures include strengthening the wedge-shape backfill material, using different transition section forms and installing under sleeper pads (USPs). The results show that strengthening the wedge-shape backfills is conducive to gradual change of the sleeper support stiffness but using different transition section forms has insignificant influences on the sleeper support stiffness. Moreover, placing the USPs at both the abutment section and the backfill section is better than only placing the USPs at the abutment.