Understanding and modelling drainage of railway ballast

Railway track drainage has a significant effect on both the response of a rail to loading and the durability of the ballast and sub-ballast. Although various standards and design methods exist for the surface drainage there is limited information on sub-surface drainage. In particular there is a paucity of analytical or numerical studies of drainage of track foundations. The present study re-evaluates results of a laboratory-based investigation of track drainage. A time-variant numerical model, based on the Dupuit–Forchheimer approximation, was developed to reproduce the experimental results. The model was also used to show the importance of the slope of subgrade and the ballast/sub-ballast permeability ratio in reducing the water retention time in the track support layers. The numerical model has practical applications as it can be used to evaluate groundwater conditions beneath the track for rainfall storm return periods and can thus be used to design track drainage.