Size of Ballast
The size of the ballast used in railway track varies from 1.9 cm to 5.1 cm. The stone of size larger than 5.1 cm is not preferable due to poor interlocking property.
The best-recommended ballast is that which contains stones ranging in size from 1.9 cm to 5.1 cm.
The size of the ballast mainly depends upon the type of sleeper used and the location of the rail track. The following sizes of ballast are used in Indian Railway:
|Types of Sleepers and Section||Size of ballast|
|1. Wooden Sleepers||51 mm|
|2. Steel Sleeper||38 mm|
|3. For Point and Crossing||25.4 mm|
Section of Ballast
The section of the ballast layer consists of depth of ballast below the sleeper and the width of the ballast layer.
Depth of Ballast
The depth of the ballast section is an important factor as the load-carrying capacity and distribution of traffic load on formation depend much on it. The more the depth of ballast under the sleeper more will be the load-carrying capacity of the track.
For curves tracks, more ballast is required than straight tracks, because of providing superelevation. The minimum depth of ballast is calculated from the following equation:
Minimum Depth of Ballast = D = (S-W)/2
Where S = Sleeper Spacing and, W = Width of Sleeper
The minimum depth of ballast prescribed on Indian Railway is 20 mm
Width of Ballast
The width of the ballast section is also an important factor as the lateral stability of the track depends partly on the quantity of ballast at the end of sleepers.
The lateral stability increases with the increase in width of the ballast section up to a certain limit(380 to 430mm from the end of sleeper).
Required Depth, Width and Quantity of Ballast For a Standard Ballast Section
|Particulars||Broad Gauge||Meter Gauge||Narrow Gauge|
|1. Width of Ballast||3.35 m||2.25||1.83|
|2. Depth of Ballast||20 to 25 cm||15 to 20 cm||15 cm|
|3. Quantity of Stone ballast per m Length||1.036 m3||0.71 m3||0.53 m3|