The surface of rails is susceptible to certain defects in the absence of proper care and maintenance. Each defect should be dealt with carefully at the proper time.
The hogging of a joint is a phenomenon in which the two rail ends at the joint get depressed on account of the poor maintenance of the rail joint, loose and faulty
fastenings, and other such reasons. The hogging ofjoints brings about deterioration in the running quality of the track. The various techniques for removing this defect are as follows.
(a) By measured shovel packing as explained in Chapter 20.
(b) If hogging occurs on a small scale, the joint sleepers are overpacked and the fittings are tightened, which may finally remedy the defect. Use of liners and shims may also help in removing the defect in case the fittings are loose.
(c) By cropping the hogged portions of the rail (preferably 450 cm), reusing the rail after the necessary drilling of holes, etc.
(d) By dehogging the rail, i.e., removing the vertical bends on the reverse side of the rail with the help of a dehogging machine.
High joints result in a very uncomfortable ride on the track. High joints are the outcome of the following.
(a) Changes in track structure, e.g., provision of wooden sleepers in a track that is normally laid with metal sleepers. Since it is easier to maintain wooden sleepers as compared to metal sleepers, this discrepancy in the type of sleepers results in high joints, which in turn produces the effect of camel back riding.
(b) Sinking of intermediate sleepers
(c) Overpacking of joint sleepers
This defect is removed by lifting and packing the intermediate sleepers.
Blowing and Pumping Joints
A joint is called a blowing joint when it blows out fine dust during the passage of a train. The surroundings of such a joint are always coated with fine dust. A blowing joint becomes a pumping joint during the rainy season when it pumps out mud and water from the mud pockets formed below the joint. This defect is caused because of poor maintenance of the joint, particularly of the packing of the joint sleepers, unclean ballast, and bad drainage, and also sometimes due to surface defects in the rail such as scabbing. As moving loads pass over the joint, the joint sleepers get depressed and lifted up constantly. As this happens, the dust or mud gets sucked up and spreads in the vicinity of the joint. The remedy lies in
(a) deep screening the ballast below the joint and shoulder sleepers,
(b) packing the joint sleeper and shoulder sleepers thoroughly,
(c) providing proper drainage at the joint,
(d) tightening loose fittings, and
(e) adjusting the creep, if any.
Lifting of track
Normally, lifting a track becomes necessary when the track undergoes regrading. This may be due to yard remodelling, construction of a bridge, etc., or in an effort to eliminate the sags that develop in the approaches to level crossings and bridges and at other locations made vulnerable due to defective maintenance or yielding
formation. The points regarding the lifting of tracks that require special mention are as follows.
(a) A maximum of 75 mm (3 ") of the track should be lifted at a time. Whenever heavy lifting is involved, it should be done in different stages, with each lift being not more than 75 mm.
(b) On single lines, lifting should commence from the downhill gradient and continue in the direction of the rising gradient. In the case of double lines, it should proceed in the direction opposite to that of the traffic, taking care not to exceed the easement grade.
(c) Lifting should be done under the supervision of a PWI after imposing suitable speed restrictions and setting up the obligatory engineering signals.
Lowering of track
The lowering of a track becomes necessary when the track is re-graded for various reasons such as yard remodelling, provision of level crossings, etc. It should be avoided until it becomes inevitable, as lowering the track makes it unstable and is quite a difficult, time-consuming, and costly proposal.
Longitudinal Sag in the Track
Normally a track between two rigid structures such as bridges, level crossings, etc., settles due to the passage of moving loads. The settlement of the track also takes place on yielding formation owing to the weakness of the formation and the puncturing of the ballast into the formation. Whereas a longitudinal unevenness in the shape of a vertical curve may not be noticeable, an irregular longitudinal sag may make the ride on the track uncomfortable. In such cases, a proper survey of the track should be carried out, pegs should be fixed at the correct longitudinal level with the help of a levelling instrument, and the track should then be lifted. The track should not be lifted more than 75 mm at a time. An adequate quantity of ballast should be collected in advance so that both packing and lifting can be done effectively. If excessive lifting is involved, the work should be done under speed restrictions.
18.4.5 Centre-bound Sleeper
This defect is generally noticed in wooden and steel trough sleeper tracks. This defect occurs when, as a consequence of plying traffic, the sleeper starts to receive support at the centre instead of at the ends. If proper care in not taken during through packing and the middle portion of the sleeper is also packed, the defect can develop very early. Even under normal circumstances, the ballast under the sleeper ends, where the sleeper rests, gets more depressed compared to the ballast at the centre because of the impact of the moving loads and in the process the sleeper, instead of resting at the ends, stats to rest at the centre.
Centre binding of the sleepers leads to the rocking of the trains and is detrimental to the quality of the track. The defect can be removed by loosening the ballast at the centre of the sleeper. It is considered a good practice to make a small recess or depression in the ballast section at the centre of the sleeper.