Wednesday, March 28, 2018

Lifting, Lowering of Track and Creep

Lifting Of Track –

1. Lifting of track will become necessary during regarding and for elimination of minor sags, which develop through improper maintenance or yielding soil, to keep a good top.

2. Correct level pegs should be fixed at suitable intervals, before lifting is commenced.

3. Heavy lifting should always be carried out under suitable speed restriction and under the protection of corresponding engineering signals. Lifting should not exceed 75 mm. at a time so as to allow proper consolidation. The easement gradient for the passage of trains should not be steeper than 25 mm. in one rail length of 13 meters. The operation should be repeated until the required level is attained when the track should be finally ballasted, through packed and boxed, the cess being made up to proper level.

4. Lifting should commence from the down hill end carried out in the direction of
rising grade in case of single line. It should proceed in the opposite direction to traffic, in case of double line, care being taken not to exceed the easement grade.

5. While lifting track under bridges and overhead structures and in tunnels it should be ensured that there is no infringement of standard dimensions.

6. In case of curves, it is usual to set the inner rail to the correct level and grade and to raise the outer rail to give the required superelevation, care being taken to see that the cant gradient is within the permissible limit.
Lowering of Track –

1. Lowering of the track should not be resorted to except where it can not be avoided and if resorted to, it should be done under suitable speed restriction and under the protection of Engineering signals.

2. When lowering is to be done, trenches should be made across the track at every 30 M. to the final level in order to give a continuous indication, while the work is in progress. The ballast should be removed sufficiently far away from the track to prevent it getting mixed up with excavated material.

3. The procedure is to clear the spaces between the sleepers, then slightly lift the
track, break the packing beneath and level it into the space between sleepers. This material is then removed and the operation repeated until the final level is
reached. The road should then be ballasted, through packed and boxed, the cess
being cut down to proper level.

4. Lowering as in the case of lifting, should be restricted to a maximum of 75 mm. at a time and the grade for passage of trains should not exceed 25 mm. in a rail length of 13 M. As opposed to lifting, lowering should be carried out in the
direction of the falling grade

5. Work of lifting or lowering of track should be carried out in the presence of
Permanent Way Inspector.

Creep:-

Counteraction and Adjustment of creep –

(1) General.-Rails have a tendency to move gradually in the direction of the dominant traffic. It is believed to be caused by the ‘ ironing out ’ of yielding track by the moving load, augmented by braking loads, and by the impact of the wheels on the running-on ends of the rails, particularly at times when they are in a state of expansion or contraction. Among the troubles caused by ‘creep’ are –

(a) Sleepers getting out of square.
(b) Distortion of gauge.
(c) Loosening of joints.
(d) Shearing and breaking of spikes, bolts and fish-plates.
(e) Buckling in extreme cases.

(2) Causes for creep in Track –

The following are some of the avoidable causes to which creep is attributed :

(a) Inadequate toe loads of the rail to sleeper fastening and rails not secured properly to sleeper.
(b) Inadequate ballast resistance to the movement of sleepers due to poor or insufficient ballast or other causes.

(c) Inefficient or badly maintained rail joints.
(d) Rails too light for the traffic they carry.
(e) Improper expansion gaps.
(f) Decaying sleepers, uneven spacing of sleepers.
(g) Lack of proper drainage.
(h) Yielding formation resulting in uneven cross levels.
(i) Loose/uneven packing.
(j) Rail seat wear in metal sleeper road.

(3) Precautions to reduce creep –

(a) For reducing creep, it must be ensured that the rails are held firmly to the sleepers and adequate ballast resistance is available. All spikes, screws and keys should be driven home, the sleepers properly packed and crib and shoulder ballast should be compacted. Rail anchors should be provided wherever necessary.

(b) With steel trough and cast iron plate sleepers and in the case of sleepers where elastic fastenings and other fastenings with adequate toe load are used, no trouble is normally experienced. Careful watch should be kept for a series of jammed joints. Not more than six jammed joints continuously should be permitted in the case of single rails. In case of SWR not more than two consecutive jammed joints should be permitted at rail temperatures lower than “tm” in the case of Zone I and II and “tm-5” in the case of Zone III and IV. On girder bridges adjustment may be necessary at regular intervals. Anti-creep devices should be provided on the  approaches of girder bridges for adequate length.

(c) : The PSC sleepers with elastic fastenings are considered as creep resistant and therefore no other creep anchors are required. In case, excessive creep is observed on PSC sleeper road, the condition of elastic fastenings, sleepers and adequacy of ballast resistance should be examined. Action for replacement/renewal of fittings, sleepers and providing adequate ballast resistance etc. should be taken as necessary.

(4) Creep Register –

Creep registers should be maintained in the pro forma. Entries should be complete as regards kilometerage, section and length of rail, sleeper density, type and number of anchors per rail length used. Periodical readings of creep should be recorded in the prescribed pro forma. Separate page should be allotted for each km. Frequency of recording of creep should be specified by the Divisional Engineer taking into consideration the rate of creep. The Assistant Engineer should test checks the register frequently, particularly sections which are prone to creep.

(5) Creep indication Posts –

 Creep indication posts square to the track should be erected on either side of the track on the cess at intervals of about one km. These may be un serviceable rail posts with chisel mark square to the joints . The top of the post should be about 25 mm. above the rail level and the amount of creep one way or the other measured with a fishing cord stretched over the chisel marks.

(6) Permissible amount of creep – Creep in excess of 150 mm. shall not be permitted.

(7) Adjustment of creep – Adjustments of creep should be carried out in the following manner:

(a) Careful measurement of expansion gaps, as existing, should be done and appropriate length which can be dealt with in one operation should be chosen. The total amount of gap in the length should be equal to the standard expansion gap required for the temperature at the time, multiplied by the number of joints in
the length.

(b)Work should start at the running-on end of the length, commonly just beyond the points and crossings or level crossings. The work of creep adjustments should be carried out under the protection of engineering signals by the Permanent Way Inspector as envisaged. Before pulling back is commenced the keys are knocked out and fish-plates removed or eased. Correct expansion liners should be used and the rails should be pulled back with bars. If the fish-plates are removed, the bars can pull against a tommy bar thrust through a bolt hole. Next, the rail is keyed up, the bolts of joints correctly tightened up, and the expansion liner moved to the next joint, whereupon the process is repeated.

(c) It is a good practice to adjust creep before the commencement of summer. It is desirable to pull back the rails during the cool hours of the day.

(d) Mechanical and hydraulic devices are available for adjustment of creep. Such a device can be set with the wide joints behind it and the tight joints ahead of it. Expansion liners are put in all the wide joints. All keys, spikes and fish bolts are loosened. The adjuster then closes up the rails behind it by pushing, leaving a gap of some centimeters between the rail ends opposite the machine. The corrected rails are then fastened up.

(e) The machine is next attached to the rail ahead of it, keys, spikes and fish bolts
loosened for that rail and those beyond it. These rails are then pulled until only the normal expansion gap is left opposite the machine. The operation leaves some of the gaps wide and it is then necessary to fix the machines further ahead in order to close them upto normal by pulling against expansion liners.

(f) When the value of total gap existing is more than the standard expansion gap required for the temperature at the time of adjustment multiplied by the number of joints, it is necessary to provide closure rails. When closure rails are put in, a speed restriction of 30 km/h should be imposed, which should be removed, when
closure rail is changed.

(g) During adjustment of creep, the sleeper spacing should be adjusted, if necessary, special attention being given to the joint and shoulder sleeper spacing. (8) Provision of Anchors to arrest Creep –To arrest excessive creep on wooden sleepered road, not provided with anti-creep fastenings, adequate number of anchors of approved design should be provided; no anchors being provided at the
joint sleepers. Both rail seats of the sleepers should be anchored on the same side. In addition to sufficient directional anchors is being provided, back up anchors may be provided if considered necessary.

(9) Prevention of creep on metal sleeper road–

 Creep on cast iron plate sleepers should be counteracted as follows:

(a) On C.I. plate sleepers all keys should be driven in the direction of traffic on the double line and alternately in the opposite direction on single line.

(b) On steel trough road normally keys are driven as indicated. However, where heavy creep is experienced on double line, all the four keys may be driven in the direction of the creep (generally in the direction of traffic). On single line keys may be driven in the opposite direction on alternate sleepers

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