Track drainage can be defined as
the interception, collection, and disposal of water from, upon, or under the track.
It is accomplished by installing a proper surface and sub-surface drainage system.As we know, 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 This article
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
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. All drains must have an adequate gradient to enable the free flow of the collected
water.
![Types of railway drainage system Types of railway drainage system](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZJVQF3A4AwVdhe1Ejn8FOjFrgrCLdz2ae0qPK-KzPnWRK2p4cxprqRlDSrcOhUj5XgGZgU5xi8wSdihYeOtVbLv7QX-1lxI_kboutO1aVzWxmHju91HynUh07PqlAk5ZOJ_zW-mopkgg/s16000/Typical+cross+section+of+side+drain.jpg) |
Cross section of side drain
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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.
Drainage in Station Yards
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).
![Types of railway drainage system Types of railway drainage system](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnJoeb7X6M9ebZRMS7b3VX_Pt80cuySy-BX0gs5qnobWhCfBeOf8sBOxiYiqdP6BkAAfp-pSDr3OR_n-oelianHJNpK1K6SOVf0xfPIRe5flrOYIGhyh5EsonLvqz84MH8K7Z76SRdFhQ/s16000/Open+drain+between+tracks.jpg) |
Open drain |
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.
Drainage of Station Platforms
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.
![Types of railway drainage system Types of railway drainage system](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgGFE45sZiArX3jCr0v3NhaVsR-SCX_HW1-6_Gomq9VWi_a18l-3yuw3RcbSAl6XxV8pWuU6sSIRY_wQ66h39n1wxp0zeS6G3njH-ZHogZRJAN-h3tGRGYK_NNlTS77nqlSsPylbuhXIvc/s16000/Drainage+of+platform.jpg) |
Drainage of platform
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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.
Sub-surface Drainage
Water normally reaches the
sub-surface due to capillary action, seepage from adjacent areas, or percolation of
rainwater. When water reaches the sub-surface, it immediately affects the stability
of the formation.
The situation becomes worse particularly if the soil is bad.
A variety of problems arise due to the proximity of the water to the subgrade. The
nature of the problems faced and the remedial measures for the same have been discussed
in detail in this article.The various sub-drainage systems
used under different conditions are briefly summarized here.
Provision of
inverted filter Some
sub-drainage systems consist of a blanket of a non-cohesive graded material, which acts as a
capillary break.
Paving of catch
water drains The
entrance of water into the subgrade can be checked by constructing effective catch water drains
that are duly paved.
Provision of
sand piling Some
drainage systems are provided with an adequate number of sand piles of a
diameter of about 20 cm. This improves sub-surface drainage.
Drainage of
water pockets by perforated pipe Perforated pipes with a diameter of about 30 cm are provided at appropriate places to
drain off the water pockets
Cement grouting Cement can be
used to grout the water pockets so as to ease the situation.
Drainage of
water pockets by puncturing holes In special situations where water is trapped in ballast pockets because
of an impervious layer that lies over a good pervious layer, puncturing holes
into the impervious layer can help drain away the water.
Requirements of a Good Track Drainage
System
A good drainage system should
satisfy the following requirements.
Surface water
should not percolate to track One of the basic requirements of a good track drainage system is
that surface water from rains and adjacent areas should not percolate and seep
into the formation of the track.
Effective side
drains The
size of the side drains should be adequate with a proper slope, so that they effectively
carry all the surface water away.
Longitudinal
drains to be saucer-shaped The longitudinal drains provided between two tracks should preferably
have a saucer-shaped cross section so that they can collect water from both
sides.
Provision for
clearing and inspection The drains provided for drainage should be such that they can be inspected and cleared
periodically.
Drain top to be
below cess level Normally,
the drain top should not be above the cess level for the effective
drainage of the ballast bed.
No erosion of
banks The
flow of water along the slope and across the track should not cause erosion of the banks or
the slopes of the banks.
Formation to be
of good soil Ideally,
the formation and subgrade should be made of a pervious, coarse-textured
soil. Such soils are more permeable, retain less capillary water, and respond more favorably to a surface drainage system.
Proper
sub-surface drainage Arrangements
should be made for a good
subsurface drainage system to drain off the
water being retained is the track. This is more relevant in the case of
defective formations.
Proper outfall Longitudinal
drains should be designed so as to provide a proper outfall, from where the water can
eventually drain off.
Special
arrangements for waterlogged areas and other difficult situations A good track drainage system should
have special arrangements for the drainage of waterlogged areas and for all other related
perennial problems.
Need for Proper Track Drainage
Water is the greatest threat to a
railway track, and the most prominent factor that adversely affects track
maintenance is improper drainage. Excess water affects the stability of the embankment, and
the bearing capacity of the soil and its resilience to shear gets considerably
reduced. Railway engineers give maximum importance to the proper drainage of the
track and the need to do so is felt because of the following concerns.
Settlement of
embankment Excess
water may cause the embankment to settle.An unequal settlement may lead to
variation in cross levels as well as longitudinal levels thereby affecting the
safety and riding quality of the track.
Reduction in
bearing capacity
The
bearing capacity of the soil as well as its resistance to shear diminishes
due to excess water in the soil. This in turn leads to numerous problems and finally
affects the safety and stability of the track.
Failure of embankment
The
percolation of water in the embankment increases the weight of the soil on the one
hand and reduces its bearing capacity and shear resistance on the other. This
makes the formation unstable. This is a common reason for the failure of embankments,
which occurs in the form of slips.
Formation of
ballast pockets Excess
moisture leads to punctures in the formation.The constant hammering action of
running trains causes the sleepers to move up and down, resulting in ballast
pockets, pumping sleepers, and other such problems.All these factors lead to poor
riding quality.
Shrinkage and
cracking of banks The
embankment soil cracks and shrinks once excess water dries up. The
problem becomes acute in the case of poor soils. This in turn leads to many problems such
as the loss of ballast in the cracks and uneven settlement, which have an adverse
effect on track maintenance.
Adverse effects
of black cotton soil There
are certain soils, such as black cotton soil, which become plastic in
nature due to the accumulation of excess water. The formation shrinks due to change
in moisture content. The bearing capacity of the soil is greatly reduced due to
the excess water. These problems imperil the safety of the track.
Formation of
slush Slush
is formed due to the dynamic load of running trains. It is forced out, thus badly
clogging the ballast. This makes the maintenance of the track very difficult.
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