Sleepers are members that are laid transverse to the rails on which the rails are supported and fixed to transfer the loads from rails to the ballast and ground below.
Functions of Sleepers
- Hold the rail to correct gauge
- Absorb blows and vibrations of moving loads
- Support the rail at proper level in straight track and proper super elevation on curves
- Transfer load to wider area of ballast or girders in case of bridges
Requirements of an Ideal Sleeper
Requirements of an ideal sleeper can be summarized into following points
- Initial and maintenance cost should be minimum
- Its weight should be moderate to handle easily
- It should be able to absorb shocks and vibrations
- It should have sufficient bearing area
- Fixing and removing of fastening should be easy
- Should have long service life
Factors Affecting Sleeper Density
Following are some factors affecting the sleeper density
- Axle load and speed of train
- Type and section of rail
- Type and strength of sleepers
- Depth of ballast cushion
- Nature of formation
In Pakistan and India, the sleeper density varies from N+3 to N+7. For instance, if the length of rail is 13m and sleeper density is N+7, then number of sleepers per rail length will be
13+7=20 (sleeper density)
Spacing of Sleepers
- Spacing of sleepers depends upon sleeper density
- Generally the spacing of sleepers is kept uniform throughout the length of the rail but near the joints it is kept less than usual.
- Near the joint, two or three sleepers are spaced closer
- The spacing between joint sleepers, between joint sleeper and first shoulder sleeper, between first shoulder sleeper and second shoulder sleeper and between second shoulder sleeper and intermediate sleeper is different from each other and then the spacing is same between all the intermediate sleepers.
Classification of Sleepers
Depending on the material used for their manufacture, the sleepers can be divided into the following categories
- Wooden Sleepers
- Steel Sleepers
- Cast iron Sleepers
- Concrete Sleepers
