Railway track drainage design techniques
Good track drainage involves considering all possible sources of water and subsequently providing an adequate drainage system for each source. Track drainage principles are given, summarized from existing literature, including the characterization of rainfall data, surface drainage systems and subsurface drainage systems.
The use of spatial survey data in various software systems to enhance track drainage designs is illustrated. Guidelines for filtering data from laser and video based surveying systems are given and the use of polynomial regression fits to improve the precision of spatial track alignment data extracted from these collection systems is discussed.
An improved systematic ditching procedure is presented and guidelines are given for planning the undercutting width and depth to provide good track drainage out of the track substructure into the ditch. The improved ditch design procedure involves finding the optimum ditch alignment that provides the minimum soil excavation for given track conditions while discharging the water away from the track to the designated outlets. A software program was developed for this purpose. Following these procedures can improve the effectiveness of ditching and undercutting operations and potentially can cut long-term maintenance costs.
A subballast drainage approach was developed based on keeping the subballast drained since saturated subballast subjected to cyclic traffic loads will deform and may even liquefy. An analytical model was developed and laboratory flume experiments were performed for this purpose. Variables considered in the design approach include rainfall intensity, hydraulic conductivity of the subballast, subballast layer thickness, length of subballast drainage path, and slope of the subballast/subgrade interface. Design examples show potential subballast saturation can be reduced by shortening the subballast drainage path with longitudinal collectors or by using a clean subballast material such as a mixture of coarse sand and gravel.
Drainage designs for three problem sites are presented in the form of case studies as application examples. A track that experienced rapid track geometry deterioration due to potential subballast saturation after heavy rainfall is also evaluated using the subballast drainage design approach developed. This design approach substantiated the field observations.