As mentioned earlier, a good track drainage system should essentially ensure that no water percolates into the track at either the surface or the sub-surface levels, and the arrangements for the drainage of sub-surface water should be good and effective wherever required. Track drainage should be handled in two distinctive phases.
Surface drainage Surface water due to rain or snow, or from adjacent areas should be drained off properly by designing well-planned and effective surface drains.
Sub-surface drainage In case water percolates into the formation due to bad soil or such other reasons, the formation gets adversely affected and this has a bearing on the safety and stability of the track. Complete details of the same are given in Chapter 9.
In the following sections, surface drainage is dealt with in three different stages covering the entire length of the track.
(a) Drainage in mid-sections between railway stations
(b) Drainage in station yards
(c) Drainage of station platforms
19.5.1 Drainage in Mid-sections Between Railway Stations
A drainage system between two railway stations consists of the following features.
Side drains Side drains should be provided along the track in cuttings and zero fill locations, where the cess level is not above the ground level. The typical cross section of a side drain is shown in Fig. 19.1. All drains must have an adequate gradient to enable the free flow of the collected water.
Lining of drains Side drain lining is imperative on Group A routes and preferable on other routes, except those routes where the drains are in rocky strata.
Adequate opening under level crossing In order for all the water to flow out of the side drains in cuttings, adequate openings should be provided under level crossings, around trolley refuges, and around the overhead electric masts.
Catch water drain Catch water drains should be provided wherever necessary, in cuttings. Their size should be worked out according to the volume of the water the drain is expected to carry.
No surplus ballast Surplus ballast in the shoulders of the track retards drainage and encourages vegetation growth. All extra ballast should be taken out of the track and stacked in small heaps beside the track.
When planning the drainage of station yards, the following guidelines should be kept in mind.
Open surface drains Surface drains should generally be left open to make cleaning and inspection convenient. When designing in-yard drains, a velocity range of
0.5 to 1.0 m/s may be allotted for earthen drains and 1.0 to 2.0 m/s for lined (or masonry).
Saucer-shaped drains As mentioned earlier, the longitudinal drains that lie between two tracks should be saucer-shaped with curved sides. However, drains with vertical sides may be provided wherever saucer-shaped drains are not practicable.
Drain top not to be above cess level Normally, the drain top should not be above the cess level for the effective drainage of the ballast bed. However, if it is essential that a drain with a higher top level be provided in order to retain the ballast, weep holes must also be provided at the assumed cess level and the drain so designed that the water it carrier does not flow the base level of the weep holes.
Outflow and slope Wherever there is a proper outfall available at either end of a yard, the longitudinal drains provided should have their slopes facing in the direction opposite to the middle of the yard. This will ensure the minimum size and depth of the drains.
Position of ballast sections The ballast section in station yards should be the same as that on the main line.
Network of cross and longitudinal drains Every station yard should have a network of cross and longitudinal drains, whether earthen or masonry, which allows water collected due to storms to be carried away in the least possible time. The arrangements for surface drainage at water columns and carriage watering points with washing hydrants should be efficiently maintained. At these locations, Water must be adequately trapped and borne away in a pipe or a lined drain.
Open drain section Figure 19.2 shows a detailed sketch of the open drains that are provided between two tracks on a railway line.
Fig. 19.2 Open drain between tracks (all dimensions in mm)
The following points should be taken into account when planning the drainage system of a platform.
Slopes away from track Normally, all end platforms should be sloped away from the track. The details of the drainage system of a platform are illustrated in Fig. 19.3.
Discharge on non-track side All drains from platform shelters, tea stalls, toilets, water taps, etc., should be enclosed in pipes and should normally discharge or release their contents on the non-track side of the platform. Covered longitudinal drains should be provided on the platform, if necessary.
Discharge not towards run-through lines In the case of island platforms, all drains should discharge their contents on the less important side of the track and not towards run-through lines.