The doubling of a railway line refers to the construction of an additional line. This is normally done when a single line is no longer capable of carrying all the trains that ply on the section. The main steps involved in the doubling of a railway line are described here.
Engineering-cum-traffic survey This survey is conducted to examine the traffic prospects of the section and to roughly identify the quantum of work and cost involved. The Railway Board finally sanctions the work and authorizes the railway to execute the same.
Specification of work During the execution of the work, it is necessary to clearly understand and follow the standards of construction and the specifications that have been laid down. The track standard should also be decided during the survey
so that the same can be followed as the work progresses. The ruling gradient and maximum curvature are normally the same as those of the existing line.
Land acquisition If necessary, extra land can be acquired for the double-line station yard, bridges, etc., in case it has not already been done.
Earthwork The earthwork for a double line is done by widening the existing formation to suit the double line. The land where earthwork is to be done is divided into different zones and a separate contract is awarded for each zone. The earthwork is properly consolidated and is normally made to endure two rains. If the soil is of a poor quality, a blanket of an adequate thickness is provided just below the final level of the formation. The soil can also be consolidated by using a sheep foot roller or vibratory roller to achieve the desired compaction. When this is done, traffic can be allowed to ply on the track immediately after the work has been completed.
Bridges The existing bridges are extended to suit the double line. This extension is done after drawing up a plan that causes the minimum dislocation or disruption of traffic. Separate zonal contracts are awarded for major bridges, whereas minor bridges are included in the zones defined for earthwork. The work is normally so planned that it is completed in the working season lasting from October to June.
Plate laying Rails, sleepers, and fastenings are collected in track depots specifically established for the project. Normally such depots are situated at every railway station. The work of track linking is usually done by the telescopic method.
Opening for goods traffic and ballasting As soon as construction work is completed, the line is opened to goods traffic plying at restricted speeds. Ballast trains also run on the section and unload the ballast on the track, which is then packed manually with the help of beaters.
Opening the line for passenger traffic Once the line is properly packed, the same is opened to passenger traffic after obtaining the sanction of the commissioner of railway safety. The speed restrictions on the section are slowly relaxed till the trains can ply at the maximum permissible speed once again.