SLEEPERS - RAILWAY ENGINEERING

“When a train goes through a tunnel
and it gets dark, you don’t throw
away the ticket and jump off. You sit
still and trust the Engineer.’’
- Corrie ten Boom

1. Sleepers
2. Functions of sleepers
3. Requirements of sleepers
4. Classification of Sleepers
5. Timber or Wooden sleepers and its details, CSI, treatments etc.
6. Metal Sleepers its advantages, disadvantages, types etc.
7. Concrete Sleepers its advantages, disadvantages and types
8. Sleeper Spacing & Sleeper Density
References Used

 What is a railway sleepers?
 Railway sleepers are the components on which the rails are
arranged with proper gauge. These sleepers generally rests
on ballast and is also called as ties in some regions. The load
from rails when train passes, is taken by these sleepers and is
distributed it to the ballast.
 Sleepers are members generally laid transverse to the
rails on which the rails are supported and fixed, to
transfer the loads from rails to the ballast and subgrade
below.

I. To hold the rails to correct gauge (exact in straight and flat
curves, loose in sharp curves and tight in diamond crossings).
II. To hold the rails in proper level or transverse tilt i.e., level in
turnouts, cross-overs, etc., and at 1 in 20 tilt in straight tracks,
so as to provide a firm and even support to rails.
III. To act an elastic medium in between the ballast and rails to
absorb the blows and vibrations of moving loads.
IV. To distribute the load from the rails to the index area of ballast
underlying it or to the girders in case of bridges.

V. To support the rails at a proper level in straight tracks and at
proper superelevation on curves.
VI. Sleepers also add to the longitudinal and lateral stability of the
permanent track on the whole.
VII.They also provide means to rectify track geometry during
service life.

An ideal sleeper should possess the following characteristics:
I. The sleepers to be used should be economical, i.e., they should
have minimum possible initial and maintenance costs.
II. The fittings of the sleepers should be such that they can be
easily adjusted during maintenance operations such as easy
lifting, packing, removal and replacement.
III. The weight of sleepers should not be too heavy or excessively
light.

IV. The bearing area of sleepers below the rail seat and over the
ballast should be enough to resist the crushing due to rail seat
and crushing of the ballast underneath the sleeper.
V. The sleepers should be capable of resisting shocks and
vibrations due to passage of heavy loads of high-speed trains.
VI. The insulation of rails should be possible for track circuiting, if
required, through sleepers.
VII.An ideal sleeper should also have an anti-sabotage and anti-theft
qualities

Sleepers
1. Wooden
2. Metal
Cast Iron Steel
3. Concrete
Reinforced Prestressed

Wooden
Sleepers
Metal
Sleepers
Concrete
Sleepers

Wooden sleepers are regarded to be best as they fulfil almost all
the requirements of an ideal sleeper.
The life of timber sleepers depends upon their ability to resist
(i) Wear,
(ii) Decay,
(iii) Attack by Vermin, i.e., white ants and
(iv) Quality of the timber used.

I. Timber is easily available in all parts of India.
II. Fittings for wooden sleepers are few and simple in design.
III. These sleepers are able to resist the shocks and vibrations due
to heavy moving loads and also give less noisy track.
IV. Wooden sleepers are easy to lay, relay, pack, lift and
maintain.
V. These wooden sleepers are suitable for all types of ballast.
VI. They are best for track-circuited operations and moreover,
wooden sleepers are over-all economical.
Advantages

I. The sleepers are subjected to wear, decay, attack by white ants,
spike killing, warping, cracking, end splitting, rail cutting, etc.
II. It is difficult to maintain the gauge in case of wooden sleepers.
III. Track is easily disturbed, i.e.. alignment maintenance is
difficult.
IV. Wooden sleepers have got minimum service life (12 to 15
years) as compared to other types of sleepers.
V. Maintenance cost of wooden sleepers is highest as compared
to other sleepers
Disadvantages

Types of Timber
Hard Wood
(sal and teak)
Soft Wood
(chir and deodar)
 Timbers most commonly used for sleepers in India are that of
sal and teak.

 The life of the sleepers can be increased from 30% to 50% for
treated sleepers over untreated sleepers.
 ‘U’ or Untreated sleepers comprising of all the sleepers made
of wood from naturally durable species in other hand ‘T’ or
Treated sleepers consisting of the rest of the sleepers.
 Timber has millions of minute cells. The cells contain juices,
and removal of the juices and filling up the cells with a
preserving solution (salt solution or oil) is known as
treatment of sleeper or wood.

Artificial Seasoning
Artificial seasoning in kiln This is a controlled method of seasoning
the timber, normally used in the USA and other advanced countries,
under conditions of temperature and relative humidity, which are in
the range of natural air seasoning.
 Boulton or boiling under vacuum process This is a process in
which unseasoned wood is treated with hot preservative to remove
the moisture content. This is adopted in the Naharkatia depot.

Air Seasoning
Air seasoning this is the method adopted extensively for the
seasoning of wooden sleepers in India. The sleepers are stacked in
the timber yard and a provision is made for enough space for the
circulation of air in between the sleepers. The sleepers are stacked
in any one of the following ways:
(a) One and nine method
(b) Close crib method
(c) Open crib method
One and Nine method & Open
crib method
Close crip

 This is an index to determine the suitability of a particular
timber for use as a sleeper.
 This index measures the mechanical strength of timber,
derived from its composite properties of strength and hardness.
 The C.S.I. is calculated from the relation:
𝐶. 𝑆. 𝐼 =
𝑆 + 10𝐻
20
 S= Strength Index, both for green and dry timber at 12% moisture
content.
 H= Hardness Index, both for green and dry timber at 12%
moisture content.

 Minimum value of C.S.I. prescribed on Indian Railways is as
follows:
Type of Sleepers Minimum C.S.I.
Track Sleepers 783
Crossing Sleepers 1352
Bridge Sleepers 1455

L
G
Guard
rail
Bearing
plates
Sleepers
Girder or
joists
D
Bearings
Abutments or pipes
Wooden Sleepers on Bridges

Description B.G. M.G. N.G.
Length (L)- wooden
sleepers
D+30 cm
(Min. 2.4 m)
D+30
(min. 1.65 m)
D+30 cm
Minimum depth
Excluding fittings
15 cm 12.5 cm (15 cm x R) 12.5 cm
Maximum
clearance/spacing
between the sleepers
50 cm 30 cm 25 cm

4.10 Size of Timber Sleepers
Gauge Length
(cm)
Width
(cm)
Depth
(cm)
Bearing Area
Per Sleepers
(sq. m)
B.G. 275 25 12.5 0.465
M.G. 180 20 11.5 0.31
N.G. 150 18 11.5 0.209
 For bridges and points and crossings longer sleepers of thicker section viz 25 cm x 15 cm or 25
cm x 18 cm are used on the railways.
 Bearing area under each rail.= Bearing length under each rail x width of sleeper.
For B.G., Bearing area under each rail = 0.9 m x 0.25 m= 0.225 sq.m
Thus, bearing area per sleeper = 2x0.225= 0.450 sq.m
 For Girder bridges with open deck, thicker section of sleepers are used and their length also is
30 cm longer than the distance between the outside edges of the parallel girders.

 When timber sleepers become spike killed, their serviceable
portions are cut and used with tie bars in station yards (i.e.
locations of compulsory stoppage). They are not used on a track
having running traffic.
 Sometimes they are used on important bridges with suitable
tie bars. Through sleepers are also used at suitable spacings.

 Due to the growing scarcity of wooden sleepers, their high cost
and short life, metal sleepers are now being widely adopted in
India.
 Metal sleepers are either of steel or cast iron.
 Cast iron is in greater use than steel for sleepers because it is
less prone to corrosion.
Metal
Sleepers
Cast Iron
Sleepers
Steel
Sleepers

I. They (metal sleepers) should bear the tensile and compressive
stresses which come on to them.
II. They should provide sufficient area for rails, i.e., area on
ballast should be at least equal to that of wooden sleepers.
III. Tamping and packing of ballast should not disturb the sleeper.
IV. For track circuiting, insulation should be possible.
V. Metal sleepers should be overall economical as compared to
wooden sleepers.

VI. The design of metal sleepers should be such that they provide
(a) Ease in fixation and removal of rails without disturbing the
sleepers.
VII.(b) Ease in pushing out the sleepers and replacing them
without disturbing the rail and the ballast.
VIII.Metal sleepers should provide sufficient grip on the rail and
ballast to prevent the dislocation of track due to shocks and
vibrations, caused by heavy loads.

I. Metal sleepers are uniform in strength and durability.
II. In metal sleepers, the performance of fittings is better and
hence lesser creep occurs.
III. Metal sleepers are economical, as life is longer and
maintenance is easier
IV. Gauge can be easily adjusted.
V. They have good scrap value.
Advantages

I. More ballast is required than other type of sleepers.
II. Fittings required are greater, difficult to maintain and
inspection.
III. Metals, C.I., or steel, are liable to rusting/corrosion.
IV. Metal being good conductor of electricity interferes with
track circuiting.
V. Metal sleepers are unsuitable for bridges, level crossings
and in case of points and crossings.
Disadvantages

Cast iron sleepers have been extensively used in India and on a
small scale in South America.
They are of the following types:
Cast Iron
sleepers
Pot or Bowl
Sleepers
Plate Sleepers Box Sleepers
C.S.T.-9
Sleepers
Rail free Duplex
Sleepers

Cross Section and Longitudinal view of Pot Sleepers

 This sleeper consists of rectangular plates about 86.5 cm x 30.5 cm
in size with 30.5 cm side parallel to the rails and of projecting ribs
under the plates for lateral stability.
 The plates are held in position with tie bars, the connections being
similar to that with pots; gibs and cotters, distance pieces and keys
or keys alone being used.
 It provides the effective bearing area of 0.464 sq. m. per sleeper on
Broad Gauge. Both, pot and plate sleepers, can be used with flat-
footed and bull- headed rails, but they have to be casted
accordingly.
 Jaws form an integral part of the casting in case of bull-headed
rails.

The various types of cast iron plate sleepers are being used such as
I. DO plate sleeper (Denham and Olphert's sleeper).
II. Laisly Pedestral,
III. The lines patent,
IV. N.W.R. type,
V. L.K. type,
VI. K.K. type,
VII.3S/T.S.
VIII.C.S.T. 4
IX. C.S.T. 4A,
X. C.S.T. 9,
XI. Rail free duplex sleeper.

 This sleeper was standardized by Track Standard Committee. It
has been extensively used on Indian Railways for the last thirty years
and moreover, its comparatively satisfactory behavior has resulted in
the withdrawal of all the previous designs.
 It has a triangular inverted pot on either side of the rail seat, a
plate with the projecting rib and a box on the top of the plate.
 The various pieces are connected across the track by means of a rod.
 A rail seat or a chair is provided to hold the Flat-footed or Bull-
Headed rail respectively with 1 in 20 cant.
 The C.S.T.-9 sleeper for B.G., weighs 103 kg and is heavier as
compared to wooden sleeper. This can easily be assembled or
dismantled without using mechanical equipment

I. The tie bar is fastened to the plate by means of four standard
cotters. Small variation in gauge can be corrected by these four
cotters.
II. The shape of cost iron support is such as to give a stable base for
the rail, and high lateral and longitudinal stability to the track.
The mild steel two way key resists creeping movement of the rail.
III. The rail seat has 1 in 20 cant and is only 11.4 cm wide along the
rails on B.G. This narrow bearing tends to reduce the rocking of the
sleeper plate under the wave-action of the rail.

IV. The sleeper may be used in sections of track in corrosive
conditions such as saline soil, industrial wastes in the
atmosphere and for cinders and ashes dropped on the track in
case of steam traction near ash-pits. Though the cast iron plate
resists corrosion but the tiebar, cotter and key are susceptible to
it.
V. The bearing area is approximately equal to the effective bearing
area of a wooden sleeper.
VI. The cantilever ends of the rails are long which lead to battering, and
ultimately hogging of the rail end and deterioration of ballast under
the joint which finally need the replacement of sleeper.

Though CST-9 sleeprs are most popular so far on Indian Railways but
they have certain limitations in their use on modern tracks with speeds
higher than 120 km.p.h. (i.e. High and super high speed tracks).
Therefore various improved versions of these sleepers viz. C.S.T.-10.
C.S.T.-11, C.S.T-12, C.S.T.-13 and so on are being developed for use
on modern tracks in light of their performance for high speeds
suitability for maintenance using mechanized techniques, stability,
etc.

A joint sleeper of cast iron known as rail free duplex sleeper has been
used as rail joints in conjunction with C.S.T.-9 sleepers.
These sleepers are used to prevent the cantilever action between the
two supports of the sleepers at the joints.
The size of each plate is 85 cm x 75 cm and the plate accommodates the
ends of the adjoining rail.
The rails are not held to the sleepers with any fitting.
Duplex sleepers give added strength to the rail near the joint.
Their use is not very popular due to the fact that rail ends supported
on this sleeper get severely battered.

In India, thousands of kilometrage of track has been laid using steel
sleepers. The design of steel sleepers should fulfil the following
Requirements:
I. The sleepers should maintain perfect gauge.
II. It should be possible to fix the rails easily in the sleeper and
without moving the sleeper longitudinally.
III. The rail should have the sufficient bearing area on the sleeper.
IV. The sleepers should not be liable of being pushed easily out of
position.
V. The metal of sleepers should be strong enough as beams.
VI. They should be so designed that packing or tamping does not
damage the edges
VII.They should be sufficiently heavy for stability.

5.3 Steel Sleepers
 Steel sleepers, being used in India, fulfil all required conditions except the last
one.
 Therefore, the practice is to use wooden sleepers in track-circuited lengths. But
insulation with the use of synthetic rubber sole plates is now possible.
 Steel sleeper is an inverted channel with folded ends. The folded edges which
form a bulb, resist the damage caused by the packing of ballast.
 When placed on ballast, it takes a grip on the ballast and prevents its
tendency of escaping out.

I. Steel sleepers are casted in one piece.
II. The fastenings to the sleepers are less in number and simple
in nature.
III. These have inverted channel section, so light in weight and
can be easily handled.
IV. The gauge, by use of steel sleepers, can be easily adjusted
and maintained.
V. Manufacturing of sleepers can be done by a simple process.
VI. The life of sleepers is much more than that of wooden
sleepers.
Advantages

I. In steel sleepers, generally, cracks develop at rail seat which
need the use of saddle plate.
II. The sleepers, being of metal, are liable to corrosion.
III. The rounded ends of the sleepers do not prevent lateral shift.
IV. Steel sleepers like wooden sleepers do not act as insulators and
hence interfere with track-circuiting and are not suitable for
electrified tracks.
V. The cost of steel sleepers is relatively more than wooden
sleepers.
Disadvantages

Steel Sleepers
Key type
Lug or Jaws
pressed out of
metal
Loose Jaw
Type
Clip-Bolt type
Saddle or
Spring Type
 In all the above types, the cross-sectional area of
sleepers is almost the same. The difference in the
method of fixing the rails to sleepers, however, exits.

This is an improvement over the pressed jaw type sleeper.
In loose jaw type, the holes are drilled or punched in the plate to
accommodate loose jaws.
At present, spring jaws are more common.

 In these sleepers, the rail seat is strengthened by a saddle plate,
which has two holes corresponding to the holes in the sleeper, on
either side of the rail.
 The object is to strengthen the rail seat. In India, now-a-days,
loose jaw-type and four-key sleepers are commonly used.
 To increase the life of steel sleepers and prevent them from
corrosion action, they are dipped in hot coal tar before supply
but such protection cannot be renewed on the underside of
sleepers.

These sleepers were ended due to chronic shortage of good wooden
sleepers and need for better design and economy of sleepers on
sustainable basis.
These sleepers are mainly of two types:
Concrete
Sleepers
Reinforced
Concrete
Sleepers
Prestressed
Concrete
Sleepers

 Experiments have been conducted in India and abroad on
concrete sleepers and it has been proved that concrete is an ideal
material for the sleepers for the following reasons:
 They are made of a strong homogeneous material, impervious
to effects of moisture, and is unaffected by the chemical attack of
atmospheric gases of sub-soil salts.
 It is moulded easily to size and shape required by scientific
investigation. to withstand the stresses produced by fast and
heavy traffic.

I. These sleepers are free from natural decay and attacks by
vermin, insects. etc.
II. They have maximum life when compared to other sleepers,
the life under normal conditions is 40 to 60 years (as compared
to 15-20 years for wooden sleepers).
III. This is not affected by moisture, chemical action of ballast,
cinder and sub-soil salt.
IV. There is no difficulty in the track-circuiting, required for
electrifying the track.
Advantages

V. The high weight of sleepers helps in minimizing joint
maintenance by providing longer welded lengths (i.e. use of
LWR), greater stability of the track and better resistance against
temperature variation.
VI. The sleepers have higher elastic modulus and hence can
withstand the stresses induced by fast and heavy traffic.
VII.Concrete sleepers in the elastic fastenings offers an ideal track
in respect of gauge, cross-level and alignment.
Advantages

I. The weight of concrete sleeper is as high as 2.5 to 3 times of
wooden sleeper, requiring the mechanical appliances for
handling.
I. They damage the bottom edge during the packing.
II. The scrap value is almost nil.
III. The damages to the concrete sleepers is very heavy in case of
derailment.
Disadvantages

These are of two types:
I. Through type,
II. Composite or Block and tie type.
 In the through type, when concrete sleeper is stressed, cracks on
the tension side are inevitable. Though the cracks are very small
and almost invisible but they tend to enlarge with repetition of the
impact loadings of the fast trains. This is the main cause of the
failure of these sleepers.
 These composite or block and tie type of sleepers are not
subjected to same degree of tensile stress and have given
excellent results in France where a steel tie of inverted T-section
is used. It is not in use, at present.

All the disadvantages of reinforced concrete sleepers have been
eliminated by prestressing technique for sleepers. In pre-stressed
concrete sleepers, the concrete is put under a very high initial
compression.
The design is based on:
I. The maximum permissible compressive strength of 211 kg/cm².
II. The minimum cube crushing strength of concrete in the
sleeper is 422 kg/cm² at 28 days, and
III. The pre-stressed wires are stressed to an initial stress of 8.82
kg/cm².

Disadvantages
I. These are heavily damaged in case of derailments.
II. The bed of the ballast is specially prepared.
III. These are uneconomical.
IV. The standard of maintenance for the track, where these sleepers
are used, is to be kept very high.
V. They are more rigid in nature.
VI. The design and construction is complicated but even then the
desired strength is not developed at the centre of sleepers.

The space between two adjacent sleepers determines the effective
span of the rail over the sleepers. The spacing of sleepers,
therefore, in a track depends on the axle load which the track is
expected to carry and lateral thrust of locomotives to which it is
subjected.
The number of sleepers in a track is indicated by the number per
rail length. Since sleeper also provides lateral stability to the track,
so, more the number of sleepers more is the lateral stability. The
number of sleepers, however, cannot be increased indefinitely as
certain minimum space between sleepers is required for packing of
ballast. In India, this minimum distance for manual packing of
ballast is kept 30.5 cm to 35.5 cm except at joints

The number of sleepers per rail varies in India from M +4 to M+7
for main tracks, where M = length of rail in meteres (If N in
place of M is used, then 'N' is length of rail in yards).
In Britain, N+ 4 sleepers are used, while in America, M +9 to M + 11
sleepers are common in through tracks.
This large number of sleepers in America is due to use of very heavy
axle loads.
 Sleeper density: is the number of sleepers per rail length and it is
specified as (M+x or N+x), where M is the length of the rail in
metres (N is the length of rail in yards) and x is a number

Varying according to the following factors and is fixed by the
Railway Board for various axle loads.
The factors governing the sleeper density are:
I. Axle load and speed,
II. Type and section of the rails,
III. Type of ballast and ballast cushion,
IV. Type and strength of sleepers, i.e., Bearing area of a particular
sleeper on the ballast. And
V. Nature of foundation.

 Thus, if M is the length of a rail in meters, the sleeper density is
expressed as M. (M + 1), (M+2) and so on.
 For instance, if length of the rail is 13 m, 17 sleepers are
expressed as M + 4 (i.e., 13 M + 4). This (M + 4) is the density
of sleepers.
The spacing between sleepers is not uniform. Three or four sleepers
on either side of the joints are kept down close together. The joint
sleepers are still more close to avoid loosening of ballast due to
impact. In suspended joints, the space between the joint sleepers is 30
cm to 45 cm and that between shoulder and intermediate sleepers is
kept 75 cm to 90 cm respectively or as per specifications.

 If joints on curves are staggered, one additional sleepers is
provided for each joint, to make each joint a suspended joint.
 Thus for sleeper density of (M+4) on straight length, the density
on curves will be (M + 5).
 Depending upon Sleeper Density the spacing of sleepers is
fixed.
 This sleeper density can also be expressed as number of
sleeper per kilometer of track as for S.W.R. and L.W.R. (i.e.
where rails are welded and length of rails has no reference)
viz. 1540 sleepers per km. The sleeper density for S.W.R. and
LW.R. and spacing requirements are given.

Sleeper Density
(No. of sleepers per km)
Centre to centre spacing between sleepers
L.W.R Track S.W.R. Track
1660/km 60 cm --------
1540/km 65 cm 66 cm
1310/km ------- 78 cm

 Example: Find out the expression for sleeper density for a B.G.
track if 19 sleepers are used under a rail length.
Solution- Length of a rail for B.G. Track = 12.8 m 'or' say 13 m.
Sleeper density = M +x
Where,
M=length of rail in metres.
X = a factor depending upon several factors, axle load,
Section of rails, etc.
So, 19 = 13+x
Hence, x = 6.
So The expression for sleeper density, therefore, is M + 6 Ans

1. A Text book of Railway Engineering book by S.C. Saxena &
S.P. Arora, Dhanpat Rai Publications- 8th Edition 2021.
2. Railway Engineering by S. Chandra & MM Agarwal, Oxford
University Press 2nd Edition, 2013
3. https://civiltoday.com/
4. https://theconstructor.org/
5. Images from google server and book’s illustrations.

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