Drainage of railway tracks

Drainage of railway tracks is essential to ensure acceptable track performance. The cost of maintenance or, conversely, the deterioration of track components, is directly impacted by the condition of the drainage system. Incorrect drainage and saturated soils may lead to premature failure of the ballast system with frequent maintenance operations. Achieving proper drainage is not simply a matter of excavating a cross trench and letting water out of the track but is reliant on providing a free draining base. Drainage is a complex problem, factors to consider include: ballast contamination, sub-ballast gradation, slope of subgrade surface, ditch or pipe depth, longitudinal slope and expected rainfall characteristics.

The sub-ballast should be capable of allowing any rainfall that permeates through the ballast to drain away without it coming into contact with the subgrade, however the sub-ballast is not permeable enough to prevent this so TENAX TENDRAIN geocomposite can be used for cross track drainage. TENAX TENDRAIN's engineered solution to improve drainage and/or reduce frost heave potential incorporates a compression resistant, void-maintaining drainage system into the rail tracks structure.
TENAX TENDRAIN provides: a high degree of compressive stiffness to support traffic; rapid fluid transmission characteristics, equivalent to a free-draining base and a significant air void to provide a positive capillary break. TENAX TENDRAIN also possesses high tensile strength and modulus, allowing it to provide base reinforcement and subgrade restraint in addition to drainage and separation.
TENAX TENDRAIN is easy to install across the rail track section. TENAX TENDRAIN can be installed between the foundation soil and the upper layer of inert material. The geocomposite separates the two soils and prevents contamination between inert material and clay particles, preventing any accumulation of water and thus allowing for a well-drained and dry base having higher mechanical properties, design life and with no water inclusion and thus the rail track section is not frost susceptible. Water in the track substructure originates from three potential sources: precipitation onto the track, surface flow from areas adjacent to the track and groundwater flow. A complete drainage system must include provisions for handling water from all three sources.

Precipitation onto the track will enter the ballast, it will then flow laterally out of the ballast into ditches or enter the subballast. This water will either drain laterally out of the subballast or continue downward into the subgrade. Subsurface drains, such TENAX TENDRAIN geocomposites are needed to collect water flowing through the subgrade and may also be needed to help drain the subballast. Surface ditch drains can collect water from the ballast and subballast. Particularly difficult is the drainage of water between adjacent tracks or from tracks surrounded on both sides by other tracks. Not only is the drainage path to the side longer, but a suitable drainage path is more difficult to maintain.
The use of a geocomposite drainage medium, such as TENAX TENDRAIN, under the outer tracks or longitudinal drains between tracks is very often required. TENAX TENDRAIN allows optimum drainage performance especially when ballast can become saturated from rainfall by a high degree of contamination thereby causing water retention, or by restricted drainage at the edge of the ballast. Causes of this restricted drainage include, for example:

The ability of water to drain laterally also requires that the drainage path at the edge of the ballast and subballast layers are not blocked.

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