Railway infrastructure includes railway track and other structures; buildings and equipment together with the corresponding land located an railway premises, designed for the management of passenger and freight transport. Railway track, bridges and other Civil Engineering structures and signal and telecommunication installation belong to Infrastructural part of BR. Maintenance is the most essential tasks after construction/installation of any infrastructure to get the proper benefit of it during its service life.
Bangladesh Railway consiss of 12 departments namely Civil Engineering, Transportation, Com-mercial, Signal, Telecom, Electrical, Establishment, Railway Nirapatta Bahini (RNB), Medical, Estate and Stores. Civil Engineering, Signal and Telecom Department are responsible for construction and maintenance of infrastructure.
Like other railways the most important infrastructure of Bangladesh Railway is track which is also termed as permanent way. Civil Engineering department of BR is responsible for maintenance of permanent way including bridges, station yards, stations, platform shed, foot overbridge and other related structures.
Bangladesh Railway routes are of 3 categories i.e Special Primary, Primary and Secondary routes.
Three types of gauges exist in BR track structure, namely Broad Gauge, Meter Gauge and Dual Gauge.
The purposes of track are to-
(a) Carry vehicles without risk of derailment;
(b) Accept vertical and horizontal forces from vehicles;
(c) Conduct these forces through the track structure and the ballast bed into the sub-grade;
(d) Ensure good traveling comfort; and
(e) Delive a high level of operational availability.
A railway vehicle wheel transmits vertical and horizontal forces to the rail. In addition, continuously welded rails generate longitudinal forces due to temperature variations. The track is affected by quasi-static (low frequency) and higher frquency components of dyanmic force. The magnitude of the forces is a function of axle load, wheel load variation due to curvature of the running path, or due to inequalities in braking and traction effort, and the impact of wheels which are not perfectly round or concentric, or which are out of balance, on a track that itself has imperfections. The track structure has to distribute these forces so as to avoid exceeding the permissible bearing pressure on the ballast immediately under the sleepers, and on the sub-grade below the ballast.
Track System and its defects
The track reacts to the forces imposed by passing traffic with damage to individual component of the track structure, or loosening of fastenings, erosion of the underside of the sleepers and deterioration of the ballast material due to traffic loading. Ballast consists of packed loose granular material of which the grains wander, wear, and break up causing increasing geometrical unevenness and clogging of the ballast bed by fine particles and by deposition from the environment which cause drainage problems. These effects, individually or combined, result in lateral and longitudinal level variations in the geometry of track.
The safety and comfort of rail travel depend primarily on standard of track parameters as follows:
(a) Gauge variation: This is measured as deviation for the nominal gauge, which is 1676 mm for broad gauge and 1000 mm for meter gauge and is measured as the minimum distance between running faces for two rails.
(b) Unevenness: It is the deviation form uniform profile on either rail, It is measured in terms of dereference in the longitudinal level, on either rail , at the mid-ordinate of a fixed base 3.5 meters s long.
(c) Cross level: It is the relative difference in the level of two rail tops measured at the same location across as measured with the help of gauge-cum-level instrument. It is measured as the deviation from zero cross level on straight or tangent track and the deviation from the supper elevation of curves.
(d) Twist: The change is cross levels in a certain length of track is called twist, Twist is calculated by measuring the cross level difference between two locations 3.5 meters apart, The cross level difference per unit base length gives the twist in terms of mm/meter.
(e) Alignment: This is measured in terms of variation in versines taken on successive chords 7.5 meter long, with overlaps of half chords. It is measured on left rail and right rail separately.
Tolerances under loaded or unloaded condition
The measurement of gauge and alignment under the loaded or no load conditions should normally not show any change, However, cross level, unevenness and twist show a lot of variation when the track is under loaded condition compared to no load condition. The under loaded condition measurements of these parameters are therefore, important. Under loaded conditions cross levels may be more by about 66 percent and longitudinal levels more by about 100 percent and compared to the respective measurements taken under no load conditions.
Type of track tolerances
Track tolerances are stipulated depending upon the purpose. The different types of track tolerances are as follows:
(a) Safety Tolerance
(b) Service tolerance or good riding tolerance
(c) Maintenance Tolerances
The maintenance tolerances are those achieved immediately after the track is attended to .The tolerance depend upon not only on the track structure but also on tools and equipment used, method of maintenance adopted, supervision available and such other factors are as follows:
(i) maintenance tolerances are prescribed so that the results of maintenance work can be assessed for ensuring quality control.
(ii) maintenance tolerances could be laid down arbitrarily and generally would be tighter than the service tolerances .
Systems of track taintenance
(a) Traditionally, track maintenance in Bangladesh has been done by manual labor since the inception of the rail network in second half on of the nineteenth century. This systems is based on a calendar system, in which track maintenance is done cyclically on a yearly basis by permanent way gangs. The annual cycle of permanent way maintenance consists of the following three main activities, which have been described below:
(1) Systematic overhauling
It is started immediately after the monsoon is over i.e. from first October and is programmed that the whole section is completed before the start of the next monsoon i.e.by the middle of April.
The rationale of shallow screening during systematic overhauling is to improve the drainage of track for ensuring better retentivity of track parameters. Another purpose is to open the road completely on the main line and running lines in yards, once a year effecting aeration of sleepers and assessment of unserviceable materials and if possible replacement of important items to enable the track to meet the demands of traffic throughout the year .
Sequence of operations in overhauling
l Shallow screening and making up of ballast.
l Examination of rails, sleepers and fastenings.
l Examination of the underside for corrosion, the ends for cracks, the head for top and side wear, rail joints for wear on the fishing planes, fish bolts for tightness. If rails on curves wear at an unusely rapid rate, lubrication of the gauge face should be done. Rust and Dust must be removed by Jim-crowing.
l Sleepers should be inspected for their condition (split and decay) and soundness particulary at the rail seats. Broken sleepers or rotten wooden sleepers particularly when two adjacent sleepers are completely unserviceable must be replaced as nessesary . In case of wooden sleeper track, plate screws, spikes and fang-bolts should be examined for their firm grip.
l Fish plates, bolts and other fittings should be checked and tightened where necsseary. Lubricating on fish-plates and bolts should be carried out well ahed of through packing so that gang mate and other staff get an opportunity to check up the oiling done.
l Squaring of sleepers.
l Slewing of track to correct alignment.
l Packing of sleepers.
l Repacking of joint sleepers.
(2) Through packing
Program for through packing is prepared in the beginning of Octorber by Assistant Executive Engineer in consultation with the SSAE(Way) and detailed instructions are issued. This program is taken into consideration the condition of track in each gang length and other local conditions including adequacy of ballast and permanent way materials.
During October all such slacks are competely picked up and each gang length is brought into good service. Under normal conditions through packing is required to be done every year during the period October to April, for 4 days in a week. The actual number of days and detailed program shall be fixed by the Assistant Executive Engineer for each section consistent with the actual condition of permanent way materials.
Before the through packing is started the following points are to be attended to-
(a) Correction of expansion gaps and pulling back of rails and squaring of joints where required.
(b) Changing all bad sleepers and packing up joints and slacks.
(c) Any earth shoulders at the end of the sleepers should be leveled off and boxing done to the correct section.
Sequence of operations in through packing
l Opening of track;
l Ballast should be opended out, on either side of the rail seats, from end of sleeper to 450 mm inside of the rail seat for broad gauge and 350 mm for meter gauge, and to a depth of 50 mm below the packing surface without disturbing the cores under the sleepers.
l Examination of rails, sleepers and fastenings;
l Squaring of sleepers;
l Slewing of track to correct alignment;
l Packing of sleepers;
l Repacking of joint sleepers;
l Boxing of ballast section and tidying;
l Monitoning through packing work.
(3) Picking up slacks
Picking up slacks is general term used for attending to track at random locations which do not ride well, including packing low joints, correcting super elevation and alignment as a part of day to day routine maintenance of track.
Slacks usually occur on stretches of yielding formation on high banks and outings, on approaches of bridges, on badly aligned curves, where ballast is poor in quality or quantity or where drainage is defective. Attention to slacks shall be as needed, based on the results of inspections and track recording, if done. Picking up slacks shall be done where the alignment is kinky or top (longitudinal) level is uneven and the track has to be restored to normal condition quickly.
The quantum of works turned out by a gang during the day will depend on the extent of slacks. In all cases sighting is done, the defects assessed and marks made on sleepers to be dealt with in chalk. The marked sleepers should then be dealt with as in through packing care being taken to see that the packing of adjacent sleepers does not get disturbed. Normally whenever joints are to be packed up both the shoulder sleepers should also be opened under the rail seat and packed up along with the joint sleepers.
In certain cases where the conditions so demand i.e., a large percentage of sleepers needs attention in a rail length, the entire rail length should be through packed under the instructions of SSAE (way).
It is imperative that when joints are picked up, at least three sleepers on either side of joints are packed. Picking up slacks may be done, by off-track tampers. In the case of low joint, the fish plates should be slightly loosened and the joint tapped, so that the rail ends are, rendered free and are capable of being lifted. After the joint is thoroughly packed the fish plates should be tightened again.
Assistant Executive Engineer checks in detail the work of gangs at random during inspection. The results of such detailed checks are recorded in SSAE (Way)’s inspection books.
Generally through packing is done for the first three days in week, the fourth day is devoted to general maintenance of the gang length, on the fifth day through packing is resumed and on the sixth day slacks are picked up in the portion already through packed. The number of days required for picking up slacks, depends on the actual condition of the permanent way materials and local conditions.
With the installation of heavier track structure and long welded rails on some important routes of the railway network, mechanized maintenance of track using on-track machines on broad gauge and meter gauge has been ongoing. On sections to be maintained with on-track machines, a 3-tier systems of maintenance shall be adopted with the distinct components are mentioned below:
(1) Track maintenance with on-track machines
One of the main purposes of maintenance of track is to provide correct surfacing and line or alignment to track which can be sustained under actual conditions of operation. Correct surfacing implies that a place across the top of the rails at right angles to the rails is level on the straights and has the correct inclination of on curves when supper-elevation is provided.
Concrete sleepers are prone to damage by manual packing and it is also not possible to obtain the desired maintenance parameters for track level and line. Further, LWR track needs to be maintained within short window of time during the day for safety reasons. Tracks with concrete sleepers and long welded rails, when tamped effectively, have sustainable retentively of line and level. The time between repairs is increased and the consumption of materials and the cost of repairs are reduced.
The justification for mechanization of track maintenance of the concrete sleepered track shall primarily be need-based due to limitations of manual maintenance for effectively maintaining the heavier track structure. Besides long lengths of tracks on the network are laid with steel trough sleepers, which are light and can be handled by one person unlike the heavy concrete sleepers.
The main types of on-track machines for track maintenance are tie-maintenance are tie-tamping machines for plain track and points and crossings, ballast cleaning machine, shoulder ballast cleaning machine, dynamic track stabilizers, ballast regulating machine, track laying machines, special purpose machines such as mobile flash but welding plant and rail grinding machines.
(i) On-track tamping machines
Tamping Machines may be for plain track and for points and crossing Of the machines manufactured by Plasser and Theurer, machines for plain track include 06-16 Universal Tamper, 08-16 Unomatic, 08-32 Duomatic and 09-32 Continuous Action Tamping Machine (CSM) and 09-3x Tamping Express, and for points and crossings include 08-275 Unimat and 08-275-3S Unimat.
(ii) Dynamic track stablizer
During maintanance operations such as tamping, lifting, slewing and deep screening the leteral resistance of truck gets reduced, which rebuilds gradully with passage of trains. This consolidation can also be achieved faster and more effcetively by causing ‘controlled settiement’ of truck by a Dynamic Track Stabilizer.
(iii) Ballast cleaning machines
The Function of ballast cleaning machine is to cary out cleaning of ballast by removing much, there by improving drainage of truck and elasticity of the ballast bed. Basically, the machine excavates and picks up ballast by means of cutter chain and carries it to a set of vibrating screens where muck is separated and thrown out by a chute and clean ballast. is transferred back to the track.
(iv) Ballast regulating machines
The main function of ballast regulating machine is to transfer, spread and profile ballast.
Works associated with tamping of track are as follows-
To achieve good results the SSAE (Way) should carry out the following preparatory work before taking up tamping with machines:
There should be sufficient ballast in track; shortage of ballast, if many, shall be made good in advance of work by machines, shortage of ballast on the approaches of level crossings and bridges shall be recouped befoe work by tamping machine. To ensure effective paking, ballast shall be heaped up in the tamping area. The level of cess, if low, shall be made up befoere tamping.
Rails shall be examined for cracks; creep and expasion gap in rails shall be adjusted; hogged joints shall a be attended before tamping and alll fittings and fastenings like fish bolts and keys tighttened and worn out fittings be replaced.
Sleepers shall be squared and spacing adjusted; re-gauging shall be done as necessary, and brodken and mdamaged sleepers shall be renewed. Concrete sleepers should be squared and missing fittings of sleepers, if any found on inspection, should be recouped before starting the work of packing and aligning of the track by tamping machine, Pumping joints shall cleaned and and additional clean ballast shall be provided wheree necessary. Sleeper-tops shall be cleared of ballast to make them visible to thehe operator.
Prior to work by tamping machine, excessive distortion of track alignment should be rectified in advance so that good lining may be achieved with the tamping machine. Curves which are badly out of alignment should be religned. On ther curves, before starting of work by tamping machine the required measurement of the curve shall be marked on the sleepers, for the operator to follow to complete the work.
(ii) Tamping Work
l Positioning of tools
l Tamping works
(iii) Post tamping work
(2) Mobile Maintenance Unit (MMU)
The work of picking up of slacks and other related works are done with Mobile Maintenance Unit (MMU). Two MMUs are required:
(a) MMU-1 (Rail-cum-Road vehical based); One with each SSAE (Way) with a jurisdiction of40-50 Kms double Line or 90-100 Kms single line
(i) Need based spot tamping
(ii) Casual renewal and repairs except planned renewals; In-Situ rail welding
(iii) Overhauling of Level Xings
(iv) Replesment of glued joints; Rail cutting/drilling and chamfering.
(v) Permanent repairs to fractures.
(vi) Creep or gap adjustments involving use of machines; Destressing of LWR/CWr.
(vii) Loading / Unloauding of meterials & other misc.functions assigned.
(b) MMU-II-(Road Vihical Based); One with each Sub-division.
(i) Reconditioning of Turnouts.
(ii) Minor repairs to the equipments of MMU.
(3) Maintenance by sectional gangs
The Sectional gangs will perfrom the following functions-
(i) patrilling of track viz keyman’s daily patrol, Hot/cold wether patrolling Monsoon patrolling; watching vulnerble location.
(ii) Attention of emergencies viz temporary repairs of frutures.
(iii) Need based attention to bridges, turnouts, SEJs and approaches of level crossings.
(iv) Greasing of ERCs, lubrication of joints, casual changing of rubber pads and other fittings.
(v) Minor cess repairs, cleaning of drains and Boxing of ballast.
(vi) Attention to loops.
(vii) Creep and gap adjustment not involving use of machines.
(viii) Cleaning of crib ballast for effective cross draninags.
(ix) Pre & Post tamping attention.
(x) Assistance of MMU & OMU as required.
Maintenance of bridges
The Chief Engineer, along with his designated staff, is responsible for the inspection and maintenance of all bridges on the Bangladesh Railway network. Reporting to him on the bridges is the Additional Chief Engineer/Bridge under whom all officers and staff in the Bridge Branch are placed. Only for the purpose of executing substructure works on bridges, the Divisional Engineer reports to the Additional Chief Engineer(Bridge).
The Bridge Branch is responsible for the major activities related to the substructure. Additional Chief Engineer(Bridge), as head of the Bridge Branch, oversees all bridge activities in the Zone. He reports to the
Chief Engineer on all bridge maters. Bridge Branch personnel, as well as Divisional Engineers for the purpose of carrying out maintenance and repair of bridge substructure, report to Additional Chief Engineer(Bridge).
All Bangladesh Railway personnel in the line of inspection of track and bridges have a responsibility to ensure that activities undertaken are conducted with concern for the safety of workers and the public.
Bridge maintenance works
The following are the functions of the Bridge Branch-
(a) Bridge Branch is responsible for maintenance of all overhead structures, platform sheds, overhead steel water tanks, foot over bridges and all other steel structures.
(b) Inspection, investigation of strength and testing of girder bridges on a regular program basis to cover the entire section in a period of three years and maintenance of record for all girder bridges on the Railway, incorporating information about their strength.
(c) All the bridges, which are not over stressed, will be inspected in detail once in every three years, while those bridges which are over stressed will be inspected at least once every year, including providing frequent special attention there to.
(d) Inspection and investigation of strength of platform shed and foot-over bridges once in three years.
(e) Presentation of drawings including strengthening and improving bridges, on program basis.
(f) Strengthening of all under-strength girder bridges, dismantling and erection of girder bridges of spans 18.3 meter and longer and important steel structure such as platform sheds and foot-over bridges.
(g) As a policy repairs to bridges shall not be carried out in a haphazard manner. Whenever any work in connection with remedial measures (or girders is undertaken, the intention will be to renovate the bridges as a whole by provision of stepped bearing bed plates with location strips, changing of bed stones rebuilding of masonry up to 0.76 meter below the bed stones. Such works will be carried out on a program basis and shall be completed on one section before they are started on another section. Close co-operation shall be maintained with the Divisional Engineers in the preparation of programs for such works.
(h) Carry out rivet testing of all major bridges once a year.
(i) In case of new bridges the masonry work of piers and abutments are normally be done by the concerned Divisional Engineer.
(j) Painting of triangulated girder spans 30.5 meter (100 feet) and longer on a regular program basis.
(k) Oiling and greasing of flat bearings of girder spans of 18.3 meter (60 feet) and longer and roller bearings of all bridges.
(l) Assisting open line engineers in restoration of through communication during floods when called upon to do so.
(m) Carrying out miscellaneous works as repairs to water tanks and their staging, erection of wireless masts and towers on requisition by other departments.
(n) Carrying out overhauling of motor trolleys on a program basis, and carrying out repairs as and when the motor trolley is sent to the bridge workshop.
Maintenance of signalling
Signaling systems for railway infrastructure are the basis for safe, fast and reliable operation of railway traffic and transport. There are basically two purposes achieved by railway signaling- a) safely receive and dispatch trains at a station b) control the movements of trains from one station to another. Signaling system is the combination of mechanical or electrical device(s) erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal’s indication and acts accordingly. Signals exist primarily to pass instructions and information to drivers of passing trains. The driver interprets the signal’s indication and acts accordingly. The most important indication is ‘danger’, which means ‘stop’. Apart from meeting the basic requirement of necessary safety in train operation, modern railway signaling plays an important role in determining the capacity of a section.
The stations of Bangladesh Railway (BR) are classified into two categories; e.g. Block stations and the Non-Block stations. At present out of 458 stations, 338 stations operate as Block stations having different types of the Signaling system. The block stations are also classified in two major sub-groups according to the signaling arrangement, e.g. interlocked stations and non-interlocked stations. “Interlo-cking” is such an arrangement of signal apparatus that prevents conflicting movements by through an arrangement of tracks such as junctions or crossings and in some cases over the level crossing gates.
The stations having Standards-III of interlocking can allow the train running over the section with the maximum permissible speed. The presence of the Train on the track is confirmed by some arrangement of Electrical Circuit and the Rail is used as a conductor for complete the Electrical Circuit path. At present, the signaling system of BR is mainly based DC biased Track circuit and only a few sections are on Axle counting system with Absolute block system. The signaling installation was maintained in a specified period according to the Bangladesh Railway Signal manual. Maintenance & operations of the stations signaling system have been executed & ensured by the Chief Signal & Telecommunication Engineer (CSTE) and his team members of the respective zones. Station Master of the respective stations records daily operation hazards e.g. failure or disturbance of the station signaling system in a register which is known as Signal Failure Register. Divisional Signal & Telecommunication Engineer (DSTE) and his team members is responsible for closely look after those issues.
At present 135 nos. block stations of BR having Standards-III Computer-Based Interlocking and Signaling System. 35 stations Standards-I to Standard-II Double wire, 48 stations having Standards-I Mechanical and 38 stations having Standards-I to Standard-III Relay Interlocked System. Remaining 82 stations have Non-Interlocked System. According to Bangladesh Railway Master Plan, all districts headquarter will be connected by Rail Route and the entire route of the Railway will be covered by modern Signaling System and Automatic Train protection by means of Centralized Train Control (CTC) system. Phase by phase BR is starting the works as on today’s need.
Source: 1. Bangladesh Railway Way and Works Manual
2. Bangladesh Railway Information Book-2017
3. Bangladesh Railway Signal Manual through Mr. Syed Md. Shahiduzzaman, Additional Signal and Telecom Engineer (Telecom), Railbhaban, Dhaka.