Ballast in Railway : Functions & Types
A layer of broken stones, gravel, moorum or any other gritty material, packed below and around the sleepers, so that the load from the sleepers may be transmitted to the formation is known as ballast in railway.
Functions of Ballast in Railway Track
- To transfer and distribute the load from sleepers to large area of formation.
- To provide effective drainage to the track. And keep the sleepers in dry condition.
- It holds the sleepers in the position during the passage of moving trains.
- It provides elasticity to the railway track for getting proper reading comfort.
- To protect the top surface of the formation.
- To prevent the growth of weeds inside the track.
- To provide necessary resistance to track for longitudinal and lateral stability.
- To provide a firm bed for the sleepers to rest upon.
- It prevents lateral, longitudinal and vertical movement of the track.
- To provide cusion effect to the track.
- To provide effective means of maintaining evenness and alignment of the track.
Requirements of Good Ballast in Railway
- Ballast used in railway track should be tough and should be wear resistant.
- It should not get crushed under the moving loads.
- Moreover the shape of ballast should be cubical having sharp edges.
- It should not have any chemical effect on the rails and metal sleepers.
- It should resist attrition and should be durable.
- Ballast used should be non-porous and non-absorbent of the water.
- It should provide good drainage of water.
- It should be resistant to abrasion and extreme weathering conditions.
- It should be locally available, cheap and economical in price.
Standard Ballast Specifications Used in Indian Railways
- The size of ballast used under point and crossings is 25 mm.
- Quality of stone ballast required per metre tangent length of broad guage is 1.11 cu.m and for metre gauge, it is 0.767 cu.m.
- Minimum depth of ballast for broad guage is 250 mm and for metre guage it is 200 mm.
- Width of ballast for broad gauge track is 3.35 meters and for metre guage track is 2.3 metres.
Types of Ballast Used in Railway Track
Broken Stones :
These are obtained from hard stones and it should be strong, hard, tough, durable and angular. They are mostly used for high speed tracks in India. These types of ballast are cheaper in long run. The granite fulfills the condition but due to consideration of availability quartz, sandstone and limestone are used. The quality of broken stones should be such that it is neither porous nor flakes off under vagaries of weather. It’s initial cost is maximum.
Gravel Ballast :
It is one of the best material used as the ballast in railway track next to broken stones, consisting of smooth round shaped materials obtained from river bed. It is cheaper than the broken stones it’s drainage property is also good. It is useful for main lines. Washing is required if gravels are obtained from soils. This requires screening before application.
Ashes or Cinder :
The residue from coal used in locomotive and other furnaces is known as ashes. This material has fairly got good drainage property and it is widely used in railway yards and sidings to keep them dry and non-slippery during rainy seasons. The cost of material is also low and the handling of this type of ballast is not cumbersome. This type of ballast can be made available in large quantity in short period of time. This type of ballast is of corrosive quality and hence this is not used where steel sleepers are used.
The sand forms another good option for ballast. The coarse sand is preferred than fine sand. It is used on unimportant lines, sidings and marshalling yards. If the sand is free from earth and vegetables it has got excellent properties to drain off water immediately. It is cheap of available at nearby site. Sometimes this type of ballast can cause wear of rail top and moving parts of the rolling stock.
Manjur is also used as ballast where other chief materials for the ballast are not easily available. It is cheap and it has good drainage properties which is used for metre guage and narrow guage tracks having light traffic. It is soft hence it may be converted into powder under heavy load. It may have corrosive action on rail. Maintenance of track is difficult if these type of ballast is used.
Selected Earth :
For sidings and also for new laid railway track, selected earth of suitable quality is sometimes used as ballast. The main purpose of earth using on new formation is to prevent the loss of goods and expensive ballast by sinking into soft formation.
Also Read : Coning of Wheels