Design for efficient drainage of railway track foundations Available to Purchase

The efficient drainage of water from railway track support systems is critical in maintaining the stiffness of the subgrade following substantial rainfall. In a preliminary investigation, the results from a full-scale laboratory experiment of drainage through ballast and sub-ballast were examined; a numerical model was developed to represent these experimental results. That initial study is extended to consider the effect of the geometry and the hydraulic properties of the track foundation on the rate at which water drains from the system. A design methodology is presented which shows that the time for almost complete drainage depends on the permeability and specific yield (drainable porosity) of the underlying sand blanket. A number of additional conditions are examined including the slope of the subgrade, the intensity and duration of the rainfall, and the occurrence of a surcharge in the drainage ditch. The provision of a laterally and vertically permeable geocomposite directly above the subgrade can reduce the time for drainage by a factor of ten.