Evaluation of lateral stability of railway tracks due to ballast degradation

Track lateral stability is one of the most critical considerations for safe and reliable railway infrastructures. With increasing exposures to high temperatures globally, a greater expansion in continuous welded rails can induce a higher risk of track buckling, especially when track defects exist. In ballasted track structures, ballast layer holds sleepers in place and provides lateral support and stiffness to the track. Note that there are several factors influencing the lateral resistance of ballasted railway tracks. However, the effects of the progressive degradation of the ballast on the track's lateral resistance have thus far never been fully investigated. Note that the fouling conditions can be due to the accumulation of ballast breakage or external contamination, such as subgrade intrusion or coal dust, and difficult to inspect in the field. It is evidenced that track buckling can incur even if the railway track and ballast seem to be in a good condition by visual inspection. Therefore, this paper presents a more realistic model to study Single Sleeper (Tie) Push Test (STPT) conditions using the Discrete Element Method (DEM) with the objective to evaluate ballasted track lateral resistance considering different fouling scenarios. Note that coal dust, acting as a lubricant, is considered as a fouling agent. The lateral force–displacement curves of sleepers are analysed. The lateral force is derived from the sleeper-ballast contact forces obtained from three main components: sleeper bottom friction, sleeper side friction, and sleeper end force. The fouling conditions are employed by adapting appropriate model parameters to the ballast layer that represents the fouled ballast condition by coal dust in the DEM simulations. Note that the fouling layer is considered to start from the bottom of the ballast layer and is applied all the way to the top to represent the completely fouled ballast layer condition. The results indicate that fouled ballast can significantly undermine the lateral stability of ballasted tracks by more than about 50%. Track lateral stiffness may be reduced significantly due to fouled ballast layer conditions that cannot be inspected visually in the field. This may reduce track restraint and increase the likelihood of track buckling even though the degraded ballast does not have direct contact with the sleeper. Finally, the study will enrich the development of inspection criteria for ballast lateral resistance and support conditions, improve safety and reliability of rail network, and mitigate the risk of delays due to track buckling leading to unplanned maintenance.