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

The effect of soil improvement and auxiliary rails on vibrations at railway track transition zones

Railway transition zones impose a sudden change in the track-ground structure, corresponding to track stiffness variation. This creates elevated vibration levels. Therefore, it is important to define the potential solutions to minimise the dynamic effects of such change. This paper studies the effectiveness of the application of auxiliary rail and soil improvement using numerical modelling. For this purpose, 3D numerical modelling of track-ground transition zones is introduced using eight-node solid elements. Further, a perfectly matched layer method is applied for the absorbing boundary condition for the wave propagation in the soil layers. The moving train simulation is represented by a sprung mass model. The time-domain results of the proposed model agree well with field measurements collected on transition zones. Once validated, a sensitivity study is performed into placing two auxiliary rails and soil stiffness. It is found that both solutions can improve the dynamic track behaviour across the transition zones. However, the greater benefit is shown in the soil stiffening based on the material properties under the investigation. To provide insight into the application of auxiliary rails, the wider placement between the running rails offers a slight improvement in dynamic effects

The effect of soil improvement and auxiliary rails at railway track transition zones

Railway track transition zones are areas where there is a sudden change in the track-ground structure. They include changes between ballasted and slab track, bridge approaches, and tunnel entry/exits. They are often the location of rapid track deterioration, and therefore this paper investigates the use of auxiliary rails and soil improvement to minimise train-track-ground dynamic effects. To do so, a 3D finite element model is developed using eight-node solid elements and a perfectly matched layer absorbing boundary condition. A moving train load is simulated using a sprung mass model to represent train-track interaction. After presenting the model, it is validated against field data collected on both a plain line and at a transition zone. Once validated, a sensitivity study is performed into auxiliary rails and soil improvement. It is found that auxiliary rails can improve the dynamic characteristics of the track across the transition, and that more widely spaced auxiliary rails provide greater benefit compared to closely spaced ones. Regarding soil improvement, a large benefit is found, and for the material properties under investigation, the effect of soil stiffening is greater than using auxiliary rails

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.Railway Engineerin

The use of multiple models to analyse railway track ground dynamics

With the increases in train speed in recent decades, it is important to define the track-ground critical velocity to prevent high track dynamic amplification. This is affected by wave propagation in the soil layers and track supporting the moving load. Therefore, this paper investigates the important variables that influence the critical velocity and dynamic amplification based on three case studies of track-ground dynamic problems, which are: the presence of low stiffness soil layer, track shakedown and soil improvement. Three modelling strategies (analytical, hybrid analytical-numerical and 2.5D numerical) are used to analyse the different track-soil problems. The findings provide a better understanding of critical velocity and dynamic amplification. These are useful when considering a new track-ground design or improving the existing railway lines