The permanent way is combination of rails, sleepers ballast and sub grade. The rails are fitted on sleepers and are joined by fish plates. The sleepers are spaced properly on the ballast and the ballast rests on a prepared sub grade called formation. The rails, which act like girders, transmit the wheel loads to the sleepers. the sleepers distribute it to ballast which holds the sleepers in position and distribute the loads over the formation.
The permanent way illustrated various components:
Requirements of Good Permanent Way
The permanent way should be semi-elastic in nature and constructed to achieve higher speeds, better riding qualities with less maintenance cost.
So the following are the basic requirements of permanent way:
1. It should have correct and uniform gauge.
2. It should have proper level of two rails on straight track and proper super-elevation on curves.
3. It should be free from irregularities and kinks and have a correct alignment.
4. It should have a certain amount of elasticity.
5. The gradients should be uniform, change of gradient should be followed by a smooth vertical curve.
6. It should have perfect drainage system.
7. The joints, points and crossing should be designed properly.
8. All the components of permanent way i.e., rails, fittings, sleepers, ballast etc., should fully satisfy the requirements of which they have been provided.
9. They should be easy and adequate provision for renewal and replacement of the components.
Construction of Permanent Way
A new railway track is constructed in three stages as described below:
1. Earthwork and consolidation
The process of earthwork is started in cuttings or in embankment. A formation up the embankment is preferred to a formation in cutting. In India light earthwork is done manually in the direction of X-section so that the amount of lead may be reduced by manual labor. But in case of heavy earthworks, the machines are used. To have proper drainage system and the height of embankment above highest water level in the area should not be less than 60 cm.
After laying the earth in embankment for formation to the design, the process of consolidation starts. Consolidation is done by the addition of admixtures like moo-rum, decomposed rock or other suitable material. It is done by impact or vibratory methods. The earth is compacted by using mechanical devices. Water is used in the process. After final compaction of the embankment, 15 cm high earthen walls are built along and across the edges of formation. The rain water gets collected within these earthen walls which further helps in consolidation. Before proceeding to the construction of second stage, the formation should be left open for at least two monsoons.
2. Plate Laying
Plate laying is the process of laying rails and sleepers over the prepared formation. The laying of ballast on the formation is not include in the process of plate laying. The ballast is generally laid after two to three monsoons of plate laying to have a proper consolidation of embankment with the radium and traffic carried by the railway line. Plate laying is carried out by three different methods i.e., Tram line method or side method. Telescopic method and American method.
The materials for plate laying are collected and transported to site of work. The rails are fixed to the sleepers and joining of rails is done by labor force. First center line of the track is marked by means of pegs and stretching string from peg to peg. The sleepers are then laid below string with required spacing. Each rail is then marked with chalk to indicate the exact spacing of sleepers, suitable chairs are then provided below the rails. To have the proper gauge, both the rails are fixed simultaneously on the same sleepers. To provide expansion joints to rails shims or liners are used. The fish plates are then put in position and four bolts are tightened roughly and when all the sleepers are fixed to rails, the bolts are finally tightened. After the process of plate laying is completed, the packing of ballast is done by labor force called packing gang.
3. Laying of Ballast
The loaded wagons of ballast are taken to the site and unloaded into a number of heaps at suitable intervals along the track. It is then done by the workers by means of shovels. The spreading of ballast on track is done by ballast trains and packing is done by labor force. The ballast should resist crushing under dynamic loads and allow easy drainage. It should not have any chemical action on rails and its size for wooden sleepers should be 5 cm and 4 cm for metal sleepers. The minimum depth of ballast should not be less than 20 cm for broad gauge 15 cm for meter gauge and narrow gauge.