- Sleepers are transverse members of the track placed below the rails to support and fix them in position.
- Wooden, cast iron, steel or RCC members which are laid transverse to the track alignment to support the rails and to transfer the load from the rails to the under line blast are called sleepers.
- Rails have to withstand the heavy load from the locomotive, wagons & coaches in the absence of sleepers the track would just settle down.
Functions of sleepers
- To hold the rails to proper gauge.
- Two lines of rails are transversely connected & held to correct gauge.
- Support the rails firmly & evenly.
- To transfer the loads from rails to the ballast.
- Load transmitted to rail to borne.
- To provide the insulation of track for the electric field tracks of signaling.
- To provide elastic medium between the rails and the ballast.
- Load is then transmitted with diminished & distributed unit load along the sleeper length to ballast beneath.
- To provide easy replacement of rails fastening.
- To provide stability to the permanent way on the whole.
Requirements of good sleepers
- The sleepers should be sufficiently strong to act as a beam under loads.
- Proper maintenance of gauge.
- They should maintain correct gauge.
- They should provide sufficient bearing area for the rail.
- Long life
- The sleepers should have sufficient weight for stability.
- They should not be pushed out easily of their position in any direction under maximum forces of the moving trains.
- Should be provide resistance against slide.
- Should resist being pushed forward due to passage of train.
- They should not be suitable to each type of ballast.
- If track-circuiting is done, it should be possible to insulate them from the rails.
Types of Sleepers
- Wooden Sleepers
- Steel Sleepers
- Cast Iron Sleepers
- R.C.C. Sleepers
- Pre stressed Concrete Sleepers
- These sleepers are regarded t be the best as they satisfy all the requirements of good sleepers and are the only sleepers suitable for track circuiting. The life of wooden sleepers depends upon their ability to resist wear, attack by white ants and quality of timber used. Timbers commonly used in India for sleepers are Sal, Teak, Deodar and chair wood.
- Universally used since the invention of sleepers.
- Teak is not used due to high cost.
- Regarded as best sleepers as they fulfill all the requirements of an ideal sleeper.
- For B.G.- 2740 mm X 250 mm X 130 mm
- For M.G.- 1830 mm X 203 mm X 114 mm
- For N.G.- 1520 mm X 150 mm X 100 mm
- Steel sleepers having long useful period steel sleepers are in the form of inverted channels with folded ends & having thickness 12 mm.
- Maintain perfect gauge.
- Should not get pushed easily out of position.
- Contain high strength.
- Provide sufficient bearing area of rail.
- Presses to a suitable trough shape.
Cast Iron Sleepers
- The sleepers made of cast iron, known as cast iron sleepers, have been extensively used in India as compared to other countries in the world.
- They consist of two pots or plates with rib and connected by wrought iron tie bar of section of about 2.5 each pot or plate is placed below each rail.
- Plate sleepers consist of rectangular plates of size about 2-10 X 1-0.
- This type of sleeper consists of two R.C.C. blocks connected by a metal tie of inverted T-section.
- These sleepers are not subjected to any degree of tensile stress as in through type.
- R.C.C. and pre-stressed concrete sleeper are now replacing all other types of sleepers except to some special circumstances such as crossing bridges ec here timber sleepers are used.
- They may be a twin block sleepers joined by an angle iron.
- It may be single block pre-stressed type.
Pre stressed Concrete Sleepers
- Pre stressed concrete sleepers are now-a-days extensively used in Indian Railway.
- These sleepers have high initial cost but are very cheap in long run due to their long life.
- In these sleepers, high tension steel wires are used.
- These wires are stretched by hydraulic jack to give necessary tension in the wires.
- The concrete is then put under a very high initial compression.
- These sleepers are heavily damaged in case of derailment or accidents of trains.