What is Sleepers?
Functions of Sleepers
Sleepers perform the following functions:
1. Sleepers are provide stability to the permanent way.
2. To allow track insulation for electrified rail sections.
3. To bold the rails to the required gauge.
4. To support the rails firmly.
5. To provide facilities for maintaining the tracks at proper grade.
6. To maintain track alignment.
7. To absorb the vibrations of the trains.
8. To behave as elastic medium between the rails and ballast. 
9. To distribute the load from the rails to a large area of the ballast.
10. To provide facilities for easy replacement Of fastenings.
11. To provide stability to the track.
Requirements of an Ideal Sleeper
An ideal sleeper should fulfill the following requirements:
1. It should be able to maintain proper gauge.
2. It should provide sufficient bearing area for the rails.
3. It should be easy to fix and remove rails from sleeper.
4. It should be capable of resisting heavy weights.
5. It should have sufficient strength so that it can bear heavy stresses.
6. It should be of such dimensions which are unaffected by tamping.
7. It should not easily move out of its position in any direction under maximum stress conditions.
8. It should not create handling and transportation problems.
9. It should be economical in initial cost and subsequent maintenance.
10. It Should be able to resist weathering agencies.
11. It should be easily insulated from the rails if track circuiting is required.
12. It should be suitable to each type Of ballast material.
13. It should be neither too heavy nor too light.
14. It should have high scrap value.
15. It should possess anti-sabotage and anti-theft qualities.
16. It should be strong enough to resist shock and vibrations.
Types of sleepers
The sleepers are classified as follows. The selection Of a particular type Of sleeper depends upon their availability, suitability, economy and design.
1) Timber or wooden sleepers
2) Steel sleepers
3) C.I. sleepers
4) Concrete sleepers.
1. Timber or wooden Sleepers
These fulfill all the requirements of an ideal sleeper. These are used universally. The life of Timber sleepers depends upon their ability to resist wear, decay, attack by white ants and the quality Of timber used.
Various advantages of timber sleepers are :
a) Timber sleepers are easy to manufacture and cheap where locally available.
b) They are easy to handle and transport.
c) These sleepers are Suitable for track circuiting. 
d) They provide an excellent elastic medium.
e) They absorb Vibrations and shocks.
f) Timber sleepers are not corroded.
Timber Sleepers have some of the disadvantages as given below :
a) Life is less due to decay and vermin attack( 12 to 15 year) Preservatives should be used.
b) Proper gauge cannot be maintained.
c) Timber Sleepers can be easily damaged by fire.
d) Timber sleepers possess less scrap value.
e) Maintenance cost is high.
2. Steel Sleepers
Steel sleepers are mostly used on Indian Railways. It consists of rolled steel plate about 6 mm thick. The plate is formed into a trough shape with rail seat canted to I in 20. The ends are flattened Out in the shape Of a spade for retaining the ballast Steel sleepers may be key type or chip and bolt type. In key type, keys are used for holding the rails by Pressing lugs and Jaws Out of the plate itself. However, the pressed lugs give way due to the movement of the keys.
This defect is removed in the second type i.e., dip and bolt type. In this four clips and four bolts are required to accommodate the loose jaws.
Clip and bolt type steel sleeper minimises the Creep considerably. It has been noticed that the pressed lugs get loosened due to wear and during service holes also get elongated. If proper care is not taken during packing, then, they tend to become centre bound. For preventing this, ballast is removed from the centre of sleepers after packing. After this, centre bounding will not take place.
Advantages:
a) possess good scrap value.
b) They are light in weight
c) They require less number of fastenings.
d) They can be easily maintained and can adjust the gauge easily.
e) They have longer life.
f) They cannot be attacked by fungus & not susceptible to fire.
g) They provide better longitudinal & lateral stability of the track.
h) They are available in one piece.
i) They reduces creep considerably.
Disadvantages:
a) They are costly.
b) They are liable to corrosion.
c) They are unsuitable for track circuited area.
d) They may lead to battering and hogging of rail ends as they are difficult to pack at the rail joints on account of their close spacing.
e) They are damaged during accidents.
3. Cast Iron ( C.I ) sleepers
Sleepers made of cast iron are known as C.I. sleepers They are of following types :
B. Plate
C. Box
D. CST-9
E. Duplex
The advantages and disadvantages of C.I sleepers are given below Advantages:
a) They possess a high scrap value.
b) They provide more resistance both longitudinal and lateral.
c) They can be easily dismantled and assembled.
d) They can also tolerate rough handling Within limits.
e) They are well suited for the beater packing.
f) They are not affected by random dropping of fire by locomotives.
g) They are easy to manufacture.
h) They provide mole resistance to corrosion.
i) They possess more life may be upto 45 years.
j) They are suitable are for all types of ballast.
Disadvantages:
a) These type of sleepers are very costly.
b) C.I sleepers are possess less lateral stability.
c) They cannot maintain gauge properly.
d) C.I sleepers are difficult to maintain.
And Maintenance cost is very high.
e) They ate not fit for track circuiting.
f) They provide less bearing area at the rail seat.
g) They possess poor ability to retain packing due to its rigid fastenings.
h) They need more number Of fittings.
4. Concrete or RCC sleepers
Concrete sleepers were used due to acute shortage of good wooden sleepers and need for better design and economy of sleepers on sustainable basis.
It is moulded easily to size and shape required by scientific investigation, to withstand the stresses produced by fast and heavy traffic.
Concrete sleepers are mainly of two types:
A. R.C.C. sleepers.
B. Pre-stressed concrete sleepers.
Advantages and disadvantages of concrete sleepers
Following are the advantages concrete sleepers:
a) They are suitable for track circuiting.
b) They are suitable for mass production.
c) They are heavy and therefore tend to improve the track modulus.
d) They have longer life (40 to 60 years).
e) They maintain the gauge very satisfactorily.
f) These can be manufactured from local materials also.
g) They are suitable for modem tracks due to flat bottom.
h) They are more durable.
i) They are not liable to decay.
j) They are not affected by moisture, chemical action of ballast, cinder and sub-soil salt.
k) They provide more rigidity to track.
l) They require fewer fittings.
m) They are easy to maintain.
n) They are free from fire hazard.
o) There is less creep in the track laid with these sleepers.
Following are the disadvantages of concrete sleepers:
a) The initial cost Of concrete sleepers is high.
b) These are subjected to more losses during accidents.
c) These have no scrap value.
d) These need the use of superior technology for their manufacture.
e) These are difficult to replace.
f) These sleepers can be subjected to more structural defects if roughly handled.
g) The weight of concrete sleeper is as high as 2.5 to 3 times of wooden sleeper, requiring the mechanical appliances for handling.
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