Assessing the role of longitudinal variability of vertical track stiffness in the long-term deterioration

The performance of the railway system in terms of dynamic loading is depending mainly on the track support conditions. Usually, the track stiffness is used as the main parameter to describe the support conditions and is defined as the ratio of the load applied to the rail over the vertical rail deflection. Ideally that parameter is constant, but in reality this condition is very unlikely to happen. Therefore, there is non-uniform track loading and non-uniform track deterioration, generally known as differential settlement, leading to a general increment of maintenance and renewal costs. Even if it plays a major role in the system dynamics, it is very difficult to derive a measure of the actual variability of the track stiffness along the railway. There are many techniques to experimentally acquire those values, for example using the Falling Weight Deflectometer (FWD) equipment or the Swedish Rolling Stiffness Measurement Vehicle (RSDV) measuring train. However, these measures are usually very costly and limited in extension. The measuring data may not be long enough to be statistically representative, and thus it is not possible to have a clear correlation between the physical properties of the railway system and its long-term behaviour without running simulations with extended track data. The main aim of the present study is to assess the role of longitudinal variability of the vertical track stiffness in the long-term behaviour of the track degradation. In particular, new sets of track stiffness data which can appropriately reproduce the statistical properties of the real ones will be simulated. Then, the variability of the outputs of the vehicle dynamic model depending on the variability in the inputs will be statistically analysed. This is inspired in past research that highlighted the role of vertical stiffness in track deterioration, but not looking at the actual longitudinal variability of vertical stiffness as a contributing factor.