Sleeper Density & Spacing of Sleepers

Sleeper density= Number of sleepers per unit rail length (per unit track length for welded rail)

Factors affecting spacing/density

1. Axle load and speed
2. Type and section of rails
3. Type and strength of sleepers
4. Type of ballast and ballast cushion
5. Nature of formation

Minimum Density
MKS: Minimum sleeper density= M+7 (BG)
FPS: Minimum sleeper density= N+3 (MG)

Spacing is not uniform
Spacing is less at joints. As joints are weak points and more impact of moving loads.

Types of Sleepers

Types of Sleepers

1. Timber Sleepers (Wooden Sleepers)
2. Steel Sleepers
3. Cast Iron Sleepers
4. R.C.C Sleepers
5. Pre-stressed Concrete Sleepers

Requirements of an Ideal Sleeper

A good sleeper should meet the following requirements:

1. The initial cost and the maintenance cost of the sleepers should be low.
2. The fittings required for fixing the rails on to the sleepers, should be simple which can be easily adjusted during the maintenance.
3. The crushing strength of the sleepers should be more with moderate weight.
4. They should be able to maintain a perfect alignment, gauge and levels of the rails and should afford efficient adjustment and maintenance.
5. They should provide sufficient bearing area to hold the rail seats and for the ballast to be supported on, to resist the crushing due to movement of heavy axle loads.
6. The sleeper spacing should be such as to remove and replace the ballast during regular maintenance operation.
7. They should be capable to resist the shocks and vibrations caused due to fast moving vehicles at high speeds.
8. They should provide insulation facilities for track circuiting in the electrified sections.
9. The sleepers should be strong enough to withstand the pressure during packing process.
10. The sleepers should be of such a design that they remain in their positions and do not get disturbed due to movement of trains.
11. The material used for the sleeper be such that it does not attract the sabotage and the theft qualities.

Functions of Sleepers

Wooden, cast iron or R.C.C members which are laid transverse to the track alignment to support the rails and to transfer the load from the rails to the underlying ballast are called sleepers.

Functions of Sleepers:
In a railway track, sleepers perform the following functions:

1. To hold the rails to proper gauge in all situations. i.e. exact gauge along straights and flat curves, slightly loose on sharp curves and slightly tight in diamond crossings.
2. To support the rails firmly and evenly throughout.
3. To distribute the load transmitted through rails over large area of ballast underneath or to the bridge girders.
4. To hold the rails to proper level in turnouts and crossovers, and at 1 in 20 in ward slope along straight tracks.
5. To provide and elastic medium between the rails and ballast and also to absorb the vibrations caused due to moving axle loads.
6. To maintain proper alignment of the track. On curves proper cant is provided by raising the outer rail and tamping the required quantity of ballast bellow the rails.
7. To provide the general stability of the permanent way throughout.
8. To provide the insulation of track for the electrified for signaling.
9. To provide easy replacement of the rail fastenings without any serious traffic disturbances.