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.