A comparison of earthwork designs for railway transition zones

Railway track transitions are zones where there is an abrupt change in the track-ground structure. They are often the location of rapid track deterioration, which means more frequent track maintenance is needed compared to plain line tracks. With the aim of reducing maintenance, modern transition zone designs use tapered stiffness earthwork profiles to minimise train-track dynamics. However, there has been limited comparison regarding the effect of different tapered profiles on dynamic behaviour. Therefore, this paper's novelty is the investigation of the performance of different earthwork designs in smoothing stiffness transition's considering different types of improvement and also train speed. To do so, first a 3D finite element track model is developed, with support conditions transitioning from an earth embankment onto a concrete bridge. A dynamic moving train load is simulated using a rigid multi-body approach capable of accounting for train-track interaction. The model is used to study the effect of four earthwork solutions with differing stiffness tapers. For each scenario, two different track structure types (ballast and concrete slab) are considered, along with different magnitudes of ground improvement. Lastly, the effects of train speed are explored. It is found tapered earthwork solutions for ballasted tracks show greater dynamic improvement compared to slabs due to their reduced bending stiffness. Further, the more complex improvement geometries such as double trapezoid shapes offer some additional improvement at locations within 3 m of the bridge. However, when considering such tapered stiffness-based earthwork solutions, additional factors such as constructability must also be considered.