Track or the Permanent way is the railroad on which trains run. It consists of two parallel rails having a specified distance in between and fastened to sleepers which are embedded in a layer of ballast of specified thickness spread over the formation. The rails are joined to each other by fish plates and bolts or welded and these are fastened to the sleepers by various fittings like keys and spikes, etc. The sleepers are spread at a specified distance and are held in position by embedding in ballast.
The Permanent way or track consists of;
- Rails
- Sleepers
- Ballast
- Fittings and fasteners
- Formation
Rails
Rails are similar to steel girders. It is a type of rolled steel section. These are placed end-to-end over sleepers to provide a continuous level surface for the trains to move.
The functions of rails are;
- Provide a pathway that is smooth and has very little friction,
- Serves as a lateral guide for the running of wheels,
- Carry out the function of transmitting the load to a large area of formation through sleepers and ballast.
- It bears the stresses developed due to heavy vertical loads, stresses due to lateral thrust, breaking stresses, and thermal stresses.
Load bearing function of the track
The load transfer works on the principle of stress reduction – layer by layer.
- The greatest stress occurs between wheel and rail and is in the order of 30 kN/cm2 or 300 Mpa.
- Between rail and sleeper, the stress is two orders smaller and diminishes between sleeper and ballast bed down to about 30 N/cm2.
- Finally, the stress on the formation is only about 05 N/cm2.
Sleepers
Sleepers are transverse ties on which the rails are laid.
The main functions of sleepers are as follows;
- Holding rails to correct gauge and alignment,
- Giving a firm and even support to rails,
- Transferring the load evenly from the rails to the ballast,
- To act as an elastic medium between the rails and ballast to absorb vibration.
- Providing longitudinal and lateral stability,
- Providing means to rectify the track geometry during its service life.
- Distributes the axle load over a sufficiently large area of ballast.
- To provide insulation for the electrified track.
Different types of sleepers
- Wooden sleepers
- Steel sleepers
- Concrete sleepers
Wooden sleepers – are the ideal type of sleeper. Hence they are universally used. The utility of timber sleepers has not diminished due to the passage of time.
Advantages: They are easy to manufacture.
They are more useful for heavy loads and high speeds.
They are easy to handle without damage.
They are more suitable for soft formations.
They absorb shocks and vibrations better than other types of sleepers.
Disadvantages: They are easily liable to attack by vermin and weather.
Hence their life are lesser than other type of sleepers.
They are susceptible to fire.
Their maintenance cost is highest in comparison to other types of sleepers.
Their useful life is short about 12 to 15 years.
Steel sleepers – Due to the increasing shortage of timber and other economic factors have led to the use of steel and concrete sleepers on railways.
Advantages: It is more durable. Its life is about 35 years.
Lesser damage during handling and transport
Easy to manufacture.
It is not susceptible to vermin attacks.
It is not susceptible to fire.
Its scrap value is very good
Disadvantages: It is liable to corrosion.
Cracks at rail seats develop during the service.
The fittings required are greater in number.
Concrete sleepers – Concrete ties have become more common mainly due to the greater economy and Shortage of timber.
Advantages: It is more durable having greater life.
It is economical as compared to wood and steel.
Easy to manufacture.
It is not susceptible to vermin attacks.
It is not susceptible to fire.
Disadvantages: It is brittle and cracks without warning.
It cannot be repaired and requires replacement.
The fittings required are greater in number.
Ballast
Ballast is a layer of broken stone placed and packed below and around sleepers.
The main functions of ballast are;
- Distribute the load from the sleepers to the formation,
- Providing drainage as well as giving longitudinal and lateral stability to the track,
- Providing effective means of maintaining evenness and alignment of the track.
- It provides a suitable foundation for the sleepers.
- It transfers and distributes loads from the sleepers to a larger area of formation.
- It provides effective drainage to the track.
- It helps protect the top surface of the formation.
Properties of Good Ballast –
- It should be hard.
- It should be wear-resistant and durable.
- It should be non-porous and non-absorbent of water.
- It should be cheaper and easily available.
- It should not be brittle.
- It should not allow rainwater to accumulate.
FISH PLATES
The function of a fish plate is to hold two rails together. At each, joint a pair of fish plates is used.
Dog spikes:
Dog spikes are used for holding the rail to the wooden sleepers.