The influence of variation in track level and support system stiffness over longer lengths of track for track performance and vehicle track interaction

Differential settlement and development of track geometry irregularity drives the need for maintenance of ballasted railway tracks. Predicting this requires an understanding of how train loading and the resulting stresses vary and are distributed along the track and how the track responds. Irregularities, from differences in the unloaded level and deflection under load (from variation in stiffness and load) influence the wheel-rail contact force along the track. The stiffness will also influence the distribution of stress into the ground. To investigate variation in the (unloaded) track level and support system stiffness along a railway, stiffness, track deflection and sleeper level surveys were carried out along a 200 m length of track. Measurements were taken at every sleeper using total station for track level and accelerometers to calculate deflection, together with a frequency-based analysis for the track support system stiffness. A simple 2D vehicle track interaction model was used to study the influence of the unloaded sleeper level, the variation in track stiffness and any identified voiding for the performance of the track. Here, the unloaded level was more significant for the loaded level and the wheel / rail contact forces than the variation in track stiffness, which was most importance for the deflections under load.