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Essentials of Track Maintenance

Through Packing, Packing of sleepers , Picking up Slacks

Essentials of Track Maintenance


As mentioned earlier, a well-maintained track provides the base for a safe and comfortable journey. Therefore, for a track to serve its purpose well, the following characteristics are required of it.


(a)  The gauge should be correct or within the specified limits


(b) There should be no difference in cross levels except on curves, where cross levels vary in order to provide superelevation


(c)  Longitudinal levels should be uniform


(d) The alignment should be straight and kink-free


(e)  The ballast should be adequate and the sleepers should be well packed.


(f)  There should be no excessive wear and tear of the track and all its components and fittings should be complete.


(g)  Track drainage should be good and the formation should be well maintained. To achieve these standards, the major maintenance operations performed in a

calendar year are described in the following sections.



1. Through Packing


Through packing is carried out in a systematic and sequential manner as described here.


Opening of road The ballast is dug out on either side of the rail seat for a depth of 50 mm (2") below the bottom of the sleeper with the help of a shovel with a wire claw. On the outside, the width of the opening should extend up to the end of the sleeper. On the inside, it should extend from the rail seat to a distance of 450 mm (18") in the case of BG, 350 mm (14") in the case of MG, and 250 mm (10") in the case of NG.


Examination of rails, sleepers, and fastenings The rails, sleepers, and fastenings to be used are thoroughly examined. Defective sleepers are removed and loose fastenings are tightened. Any kinks in the rails are removed using a Jim Crow.


Squaring of sleepers The sleepers get out of square quite frequently resulting in gauge variations and kinks. To avoid this, one of the rails is taken as the sighting rail and the correct sleeper spacing is marked on it. The position of the sleeper is checked with reference to the second rail with the help of a T-square. The sleepers are attended to after their defects have been established, which may include their being out of square or at incorrect spacing.


Aligning the track The alignment of the track is normally checked visually, wherein the rail is visually assessed from a distance of about four rail lengths or so. Small errors in the alignment are corrected by slewing the track after loosening the cores at the ends and drawing out sufficient ballast at the end of the sleepers. Slewing is carried out by about six people by planting crowbars deep into the ballast at an angle not exceeding 30 o from the vertical.


Gauging The gauge should be checked and an attempt should be made to provide a uniform gauge within permissible tolerance limits. Table 18.1 lists the tolerances prescribed for gauge variation, keeping in mind the side wear that occurs at the time of laying of tracks. This is done to ensure a comfortable ride for the passengers, provided that uniform gauge can be maintained over long lengths.


Table 18.1   Gauge tolerance for different tracks

The gauge is adjusted in accordance with the type of sleeper under consideration as described in the following.


Wooden sleepers In the case of wooden sleepers, gauge adjustment is possible only by removing the dog spikes and refitting them at a new location. Therefore, gauge adjustment should be avoided as far as possible unless the gauge is quiet irregular. When the gauge must be adjusted, all the spikes on the inside and half of those on the outside are removed while the remaining half are loosened. The old spike holes are plugged and new holes are bored in correct places. The gauge on each sleeper is adjusted and the spikes are re-driven.


Steel trough sleepers In the case of steel trough sleepers, gauge adjustment is done with the help of keys. When the gauge is slack, the keys on the inside are loosened while those on the outside are driven. The procedure is reversed when the gauge is tight. The maximum possible adjustment of the gauge is 2.5 mm to +4.0 mm.


CST-9 sleepers In the case of CST-9 sleepers, gauge adjustment is done with the help of cotters. Normally a gauge is adjusted by 5 mm. The maximum extent to which a gauge can be adjusted -3 mm to +10 mm. It has been noticed that adjusting the gauge may sometimes disturb the alignment, which is taken care of prior to gauging as per the standard practice. In such cases, the track has to be realigned once gauging is completed.


 Packing of sleepers


The base rail is identified by the mate and the dip or low joints are lifted correctly to ensure that the longitudinal level of the rail is perfect. The sleepers are then packed by applying the scissors packing method. Four men tackle one sleeper simultaneously, two at each rail. The ballast under the sleeper bed is properly packed by the men who stand back to back and work their beaters diagonally by lifting them up to chest level. While the packing is being carried out, the second rail is brought to the correct cross levels thereby ensuring perfect surfacing of the track. In the case of wooden and steel trough sleepers, it should be ensured that the sleepers are not centre-bound and that as such the trough is made in the ballast section at the centre of the sleepers. After packing is completed, the alignment and top should be checked carefully and minor adjustments made as needed.


Repacking of joint sleepers The joint sleepers are then packed once again and the cross levels checked.


Boxing ballast section and dressing Afterwards the ballast section is properly boxed and dressed with the help of a special template. The cess should also be dressed or covered similarly and its level maintained in a way that proper drainage is ensured. Through packing follows a programme which requires that it is undertaken after the monsoon and that it extends from one end of the section to the other. Through packing must be carried out at least once every year.


A gangman normally accomplishes about 11 m to 12 m of through packing on BG, 16 m to 17 m on MG, and 23 m to 24 m on NG tracks.



2 Systematic Overhauling


The track should be overhauled periodically with the object of ensuring that the best possible standards of track conditions are met and maintained. The systematic overhauling of the track should normally commence after the completion of one cycle of through packing. It involves the following operations in sequence.

(a)  Shallow screening and making up of ballast section


(b) Replacement of damaged or broken fittings


(c)  All items included in through packing


(d) Making up the cess


The frequency of overhauling depends upon a number of factors such as the type and age of track structure, the maximum permissible speed and volume of traffic, the mode of traffic, the mode of traction, the rate of track deterioration, and the amount of rainfall in the region. On the basis of these factors the chief engineer decides, the length of the track to be overhauled but normally the plan is so drawn that the systematic overhauling of a section is completed in about 3 to 4 years. The stretch of track to be tackled in a particular year should be in continuation of the length overhauled during the previous year. If possible, gap adjustment, including joint survey and adjustment of creep, should be done prior to systematic overhauling.


Lubrication of rail joints


The lubrication of rail joints is an important part of the work done on the permanent way and is incidental to systematic track maintenance. Joints are lubricated for the following purposes.


(a)  To allow for free expansion and contraction of rail


(b) To reduce wear and tear on the fishing planes of rails and the fish plates All rail joints, are lubricated once a year during the moderate season. This is


also known as the oiling and greasing of fish plates. This work is not done during the rainy season. The lubricant used is a paste of workable consistency that consists of the following proportions of plumbago, kerosene oil, and black oil.


Plumbago (dry graphite) 5 kg Kerosene oil (second quality) 3.5 L Black or reclaimed oil 2.75 L


For 100 joints of 52 kg/90 R or for 125 joints of 75 R/90 R sometimes only plumbago and kerosene oil are used in the ratio of 3:2 for lubricating fish plates. Black oil is, however, used for oiling fish bolts and nuts.


Rail joints should be lubricated only after ensuring that their surfaces are properly cleaned, preferably with the help of wire brushes and clean jute. Joints should not be lubricated in extreme temperatures or when the rails are in tension as a result of creep. Joints should be opened one at a time for lubrication. Even when opening a joint, only one fish plate should be tackled at a time and at no time during the operation should there be less than one fish plate and three fish bolts connecting the two rails.



3 Picking up Slacks


Slacks are those points in the track where the running of trains is faulty or substandard. Slacks generally occur in the following cases.


(a)  Stretches of yielding formation


(b) Poorly maintained sections that have loose packing, bad alignment, and improper longitudinal and cross levels


(c)  Improperly aligned curves


(d) Approaches to level crossings, girder bridges, etc., particularly in sags


(e)  Portions of track with poor drainage


(f)  Sections with an inadequate or unclean ballast cushion


(g)  Other miscellaneous reasons


In every working season, a certain number of days in each week (normally one or two days) are allotted to the picking up of slacks, depending upon the monsoon pattern and other local conditions. However, no through packing is done during the rainy season and slacks are only picked up in order to keep the track safe and in good running condition. In areas with less than 750 mm of rainfall, the alloted time may not be used only to attend to the slack but also to carry out through packing.

Slack may be sometimes picked up by packing only the following segments of the track.


(a)  Joint sleepers and the two other sleepers on either side of the joint, i.e., first shoulder and second shoulder sleepers


(b) A few sleepers in the approaches to level crossings and bridges


(c)  Intermediate sleepers


(d) Stretches of track that adversely affect the running of trains as revealed by inspection notes


It may be noted here that points and crossings should be attended to throughout the year. In sections with no points and crossings, the alloted time may be utilized for creep adjustment and other such track maintenance work. Two separate charts, one for main line work and another for yard work, are maintained by each gang and kept in the personal custody of the gang mate.


A recommended annual programme is drafted for regular track maintenance, in which each major activity is specified a certain time slot as per a fixed timetable (calendar). Table 18.2 shows the timetable for regular track maintenance. Concrete sleeper tracks are maintained by on-track tie tamping machines. Details of the annual programme drawn up for the maintenance of concrete sleeper tracks are given in Chapter 20.


Table 18.2   Timetable for regular track maintenance

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