Permanent Way design Notes 1

RDSO Proposed BG Turnout Speed Restrictions

TurnoutSpeed Restriction

1:8.5 turnout with straight switch 10 km/h1:8.5 turnout with curved switch 25 km/h1:12 turnout with straight switch 15 km/h1:12 turnout with conventional curved switch (0°27'35" switch entry angle)

40 km/h

1:12 turnout with improved curved switch 50 km/h1:12 turnout with thick web switch 50 km/h1:16 turnout with symmetrical split curved switch 75 km/h1:16 turnout with conventional curved switch 50 km/h1:16 turnout with high speed curved switch 60 km/h

Specifications and Track Construction

Q. What are the dimensions of IR track formations?

Please consult the diagrams available on the following pages:

Track Formation Diagram : This page shows a cross-section of a typical track formation showing the different components that make it up and the usual terms associated with them.

Track Dimensions Diagrams : This page shows dimensions for common types of tracks (MG and BG), both single line and double lines, on embankments and in cuttings.

Q. What weights and kinds of rails does IR use?

Broad Gauge The IRS standard for most mainline tracks is 52kg/m (really 51.89kg/m, 105lb/yd), and it allows 25-ton axle loads. Until about 1970, most sections had RBS standard rails of 44.7kg/m (90lb/yd). The RBS standard had been adopted in 1914, and allowed 22.5-ton axle loads at 100km/h. It is still found in many places. For sections with heavy traffic,

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the newer IRS standard rails are 60kg/m (really 60.34kg/m, 130.4lb/yd). A 62kg/m standard has been mooted. For BG branch lines, the commonly used rail weights are 37.2kg/m (75lb/yd), 42.2kg/m (85lb/yd), and 44.7kg/m (90lb/yd) (these are also being replaced now by the standard 52kg/m weight). See table below.

Although rails allowing 22.5t or 25t loads are in place, as a matter of operating procedure goods wagons are currently [5/05] restricted to 20.3t axle load. There are proposals to raise this to 23t.

Traffic DensityGMT/yr

Broad-gauge Routes and their Rail Weights

A B C D Spl D E Spl E

> 20 60kg 60kg 60kg 60kg 60kg 60kg 60kg

10-20 60kg 60kg 60kg 60kg 60kg 60kg52kg 90UTS

5-10 60kg52kg 90UTS

52kg 90UTS

52kg 90UTS

52kg 90UTS

52kg 90UTS

52kg 90UTS

< 552kg 90UTS

52kg 90UTS

52kg 90UTS

52kg 90UTSor 60kg SH

52kg 90UTSor 60kg SH

52kg 90UTSor 60kg SH

52kg 90UTSor 60kg SH

Loop Lines

52kg SH 52kg SH 52kg SH 52kg SH 52kg SH 52kg SH 52kg SH

'SH' = Second-hand

Q. What are the common lengths of rails?

The most common length for BG rails is 13m (42'8'') although double-length rails (26m, 85'4'') are seen in some places. MG rails are usually 12m (39'4'') in length. NG rails vary, but the commonest length is 9m (29'6''). Much earlier (before the metric system was adopted!), rails were generally produced in sizes of 11, 12, or 14 yards (33', 36', 42'), less commonly 13 yards (39') or 10 yards (30' - NG).

Welded rail sections are of two types: Short Welded Rail or SWR which consists of just two or three rails welded together, and Long Welded Rail or LWR which covers anything longer. (In the past, there was a distinction made between LWR and Continuously Welded Rail, or CWR, based on the length -- in CWR, the total length was 0.75km or more. The term

'CWR' is no longer used although you may still find it in old documents or painted signs.)

Q. What are the 'thick web switches' ('thick webbed switches')?

The term thick web switches most commonly refers to a new [2002] design of sturdier BG switches on prestressed concrete sleepers, which can handle higher turnout speeds. These are made for 1:8.5 turnouts (less commonly, 1:12), with 160mm (less commonly 115mm) throw, and have clamp locks, spring setting devices (SSD), and the ZU-1-160 thick web rail. In 2003 or 2004, IR decided to use these switches on all the Class A routes and other high-density routes with traffic above 20GMT/year. The new switches have been designed to be easily installable on top of existing prestressed concrete sleepers supporting older switches.

Q. What types of welding are used for rails?

Principally two types of welding are used for rails. One is Flash Butt Welding, and the other is Alumino-Thermic Welding, also known as Thermit(e) welding. A third kind of welding, known as Gas Pressure welding, is used much less often, and a fourth kind, Metal Arc Welding, is very rarely used.

In Flash Butt Welding, a strong electric current is passed through the metal body of the rail in the vicinity of the spot which is to be welded, and the resistance of the rail to the current results in localized heating which melts the metal. No additional material is added, and the parent metal of the rails itself forms the material of the weld. About 25mm to 35mm of the rail length is consumed in the melting process. Flash butt welding is done in mostly automated way using a machine that clamps and firmly holds together the two ends of the rails to be welded. When the two end surfaces are close together and the electricity turned on, the current arcs over or 'flashes' at the junction between the rail ends

In Thermit Welding or Alumino-Thermic Welding, the two ends of the rails are not brought into contact; instead, the gap between them is filled with molten material created by the exothermic reaction of aluminium and iron oxids

Flash butt welding is generally considered to be superior to thermit welding because it is essentially a forging process and the material of the

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weld is chemically identical to the parent body of the rails, which means its strength and other characteristics are almost identical to those of the body of the rails. Flash butt welding also typically results in fewer defects such as contaminant particles, porosity, etc., at the weld. Thermit welding also requires a higher quality of rails as a precondition -- rails that are corroded, twisted or warped, hogged or battered, or excessively worn cannot be welded by the thermit process as faults can propagate into the weld material and cause weld fractures.

Other Methods. Gas Pressure Welding a solid phase welding technique. Oxy-acetyline flames are used to heat the ends of the rails to be welded to 1200°-1300°C, and they are then placed in contact with one another at high pressures, leading to the formation of a solid bond.

Q. What kinds of rail joints does IR use?

Fishplated joints are the most basic joints seen, on lines where there is no track-circuiting, and no welded rail in use. Fishplated joints are so called because of the use of a fishplate, which is a bar that is attached by means of bolts (fishbolts) to the rails on either side of the joint. Usually there are two bolts securing the fishplate on either side. There are variations in the basic fishplate design to account for different weights of rails, and joints in special situations such as on sharp curves, at points, etc. For 60kg/m track, while the rail specification is very close to Revised British Standard, the fishplates (and fishbolts) are considerably stronger than the British standard specifies. Combination fishplates are used to secure rails of different weights or different profiles together at a joint. Expansion joints or "rail expansion joints" are provided in welded rail sections and other places where it is desirable to allow the rails to expand and contract with the varying temperature. (See below.) Special fishplates are used for expansion joints (different types for different weights of rails, and also for simple expansion joints and special expansion joints with central rail pieces.

Insulated rail joints are used in places where it is essential to keep adjacent rails electrically insulated from each other for the purposes of track circuiting or signalling. Insulated rail joints (also known as "block joints" in some cases) are of three types. Class A joints are an older type, made of wood to achieve the electrical insulation. Class B joints use Nylon 66 (and are hence known as "Nylon insulated rail joints") to achieve the insulation. Class C joints are glued insulated rail joints quite commonly seen now on most high-speed lines. G3(L) joints are longer and use 6 fishbolts; G3(S) joints are shorter, and use 4 fishbolts.

Q. What are expansion joints?

Expansion joints (or 'switch expansion joints') are joints provided at intervals in the track to allow space for rails to expand in hot weather. Earlier expansion joints were simply gaps between the ends of adjoining rails. These gaps result in a lot of violent shocks to the vehicles riding on the rails and besides, limit the lengths of rails that can be used. Newer expansion joints have the neighbouring ends of rails mitred or tapering with diagonal cuts so that as they expand they can slide past one another to some extent. This allows for longer welded rail segments to be used and also reduces the shock to passing vehicles. In some cases, such as girder bridges with long (over 30.5m) spans, special expansion joints are provided where a short central piece of rail, not keyed to the sleepers, is provided in between the two long rails that meet at the joint; the central rail is also mitred as are the two long rails on either side, so that the effective expansion gap available is twice as long as in the standard mitred expansion joint.

Thermal expansion of rails is often arrested by the provision of heavy RCC sleepers (280kg weight) and firmly clipping the rails to the sleepers. This prevents thermal expansion from propagating to the ends of the rails, except for a section near the ends ('breathing length') that is allowed to expand. Such expansion joints are provided once every 3km to 4km on most sections today, and especially close to distant signals or advanced starters where track-circuiting begins.

Q. What are the usual neutral temperatures for continuously welded rail? What equipment does IR use for track destressing?

IR divides the country into five zones based on the normal temperature variation expected in each region. The maximum rail temperature difference is about 70C (ranging from a minimum of -5C to a maximum of 60C or so -- the rail temperature can be several degrees higher than the ambient temperature. The neutral temperature or stress-free temperature for CWR is usually fairly high, 40C or even higher in some locations depending on expected summer temperatures -- it is usually 5 to 10C higher than the expected mean temperature for the zone's range.

Track destressing is carried out when the ambient temperature is high, not much below the maximum that is normally attained in the area. Switch expansion joints (SEJ) are provided at the ends of long welded rails to allow for the cumulative thermal expansion movements of the ends of the

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rails. Most SEJs allow for a movement of the ends of the rails of about 120mm, but there are some SEJs with a maximum gap of about 190mm.

Rail fasteners used by IR are of the type that completely resist longitudinal motion of the rails. A lot of track destressing is still done manually, but IR also uses hydraulic track tensors to destress and pretension rails. The unfastening and fastening of the sleepers is also usually done manually.

Q. What kinds of sleepers are used by IR?

Cast iron sleepers ('CST-9') are widely used. They are not very suitable for high-speed traffic and so are not usually seen on the mainline BG sections. The earlier 'pot sleepers' were especially prone to problems; newer cast iron sleepers (with ends that have two pockets) are much more laterally stable. Steel trough sleepers ('ST') are very common, especially for many high-traffic BG routes. Steel sleepers of various designs have also been used for MG and (by reusing discarded MG sleepers) for NG too.

IR also uses prestressed (pretensioned) concrete sleepers in many areas. Some are monobloc prestressed concrete sleepers, while others are two-piece reinforced concrete sleepers. These came into use in the 1970s, however the twin-block concrete sleepers have gone out of use while the monobloc sleepers continue to be deployed. Standard prestressed concrete sleepers are available for a number of configurations for use in turnouts. Some post-tensioned concrete sleepers do exist on some stretches of track, but these are no longer being manufactured as the factory at Subedarganj, Allahabad, which used to make them has switched to making pretensioned sleepers now. Steel channel sleepers, consisting of two steel channels placed back to back, are used on bridges. These use special polymer or rubber pads between the bridge girders and the sleeper bottom and also below the rails for damping.

The most common sleepers used to be the wooden sleepers, but these are now not seen much anywhere except on bridges and at turnouts, and on branch lines and at remote locations. These may be untreated (from durable woods like teak or sal that have natural resistance to vermin and weather wear) or treated (from softer woods such as deodar, usually heat- and pressure-treated with chemicals such as creosote and furnace oil).

Wooden sleepers are used on bridges and turnouts because they are very easily cut and sized on site to fit the peculiarities of the particular stretch of track. Wooden sleepers were also preferred for bridges because they are lighter compared to the concrete sleepers, and provide additional damping for vibrations

A few stretches of track have ballastless concrete beds with no sleepers

Q. What rail fasteners does IR use?

IR uses various kinds of Pandrol design fasteners, ERC Mark III (850-1100kg toe load), and ERC Mark V (1200-1500kg toe load) (the latter developed by RDSO). Pandrol 'J' clips, often yellow in colour, which have a lower profile and lower toe load), are used where they need to be removed and reinserted easily and where ordinary clips might interfere with the fastening of fishplate bolts.

Q. What sleeper spacings does IR use?

Broad Gauge (See table below.) Most BG mainline sections now have about 1660 sleepers per km (about 60cm spacing); the earlier standard used to be 1538 sleepers per km (about 65cm spacing). BG branch lines may have 1540 sleepers per km (about 65cm spacing) or 1340 sleepers per km (about 75cm spacing); the older standard was 1307 sleepers per km (about 76cm spacing). Minor or lightly used BG lines used to be built with about 1154 sleepers per km (about 87cm spacing). These figures apply mainly to the traditional wooden sleepers.

Traffic DensityGMT/yr

Broad-gauge Routes and their Sleeper DensitiesA B C D Spl D E Spl E

> 20 1660 1660 1660 1660 1660 1660 166010-20 1660 1660 1660 1660 1660 1660 1540< 10 1660 1540 1540 1540 1540 1540 1540Loop Lines 1340 1340 1340 1340 1340 1340 1340

While the minimum sleeper density is M+4 for short welded rail (see below for explanation of notation), for up to 6 rails abutting an SWR section, the sleeper density is M+7.

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Q. What does the notation 'N+4' or 'M+3', etc., mean in describing sleeper densities?

This notation is an old one. The 'N' or 'M' in this stands for the length of a rail in yards. The additional number specified represents the excess of the number of sleepers over the number of yards for a rail. E.g., 'N+3' for 11-yard (33') rails indicates 14 sleepers (11 + 3) for each rail. This was a convenient formulation, especially when rails were manufactured to sizes of 11, 12, or 14 yards. Before the days of mechanized track laying, it was common to see track laid where the sleeper density was not uniform, with some bunching up of sleepers towards the end of each rail, with adjacent sleepers at the ends of neighbouring rails being less than a foot apart in some cases.

Q. What is the relationship between speed, turning radius, and track cant? What are the cant excess / deficiencies specifications for IR tracks?

Super-elevation, or cant, is provided to counteract the centrifugal tendency of trains on curves. On a canted curve (where the outer rail is higher than the inner one of the curve), the weight of the vehicle provides a component that counteracts the centrifugal tendency. Cant excess refers to the condition where the cant or superelevation is too much for the permitted speeds on the curve, while cant deficiency refers to the condition where the track is not canted enough for the speed of the trains.

On BG track, cant excess and cant deficiency tolerances are 75mm. In special cases, cant deficiency can be as high as 100mm on sections with speeds of over 100km/h on 'A' and 'B' category routes. Maximum cant is 165mm on 'A' and 'B' routes, and 140mm on 'D' and 'E' routes.

The formula relating the maximum speed on a curve with the cant and cant deficiency is:

        Max. speed = 0.27 * √((cant + cant deficiency) * radius)where the cant and cant deficiency are in mm, the radius of the curve is in meters, and the speed is in km/h. Using this formula it may be seen that with a cant of 165mm and cant deficiency of 75mm, the radius for a curve allowing 100km/h traffic is 571.6m. Any curve sharper than this must have a speed restriction on a 100km/h section.

Q. What kinds of ballast does IR use?

For all high-traffic lines, IR uses machine crushed hard stone ballast, usually from locally quarried granite stone, or crushed basalt. In the past, broken brick, slag from metal processing, cinders, and waste construction material were also used.

For most sections with wooden sleepers, the ballast is of a 6.5cm nominal size (not more than 5% retained on a 65mm square sieve, 40%-60% retained on a 40mm square sieve, and at least 95% retained on a 20mm square sieve). In the past, ballast of 5cm nominal size was extensively used, and smaller ballast of 4cm - 2.5cm was used for iron or steel sleepered track, points, etc. The ballast layer is 0.15m-0.25m thick on most lines but is up to 0.3-0.35m in newer trackwork, especially for high-traffic lines with prestressed concrete sleepers. The sides of the ballast layer generally slope at a 1.5:1 incline.

A few sections of IR have ballastless concrete bed track: much of the Calcutta Metro, a few sections of Konkan Railway, the second phase of the Chennai MRTS project (about 8km of the elevated portions of the route, with design speeds up to 100km/h).

Q. What sort of sub-ballast, blanket, and subgrade layers are provided in the track formation?

IR generally does not use a separate sub-ballast layer below the ballast layer. A blanket layer of coarse, granular material is usually provided directly below the ballast layer. Blanket layers are not provided for tracks on rocky beds, or on well-graded gravelly or sandy beds.

Blankets of at least 45cm thickness are provided for tracks laid on poorly graded gravel or sand beds, or on silty gravel or silty / clayey gravel beds. Blanket layers of 60cm are required for clayey gravel, clayey sand, silty sand, or clayey / silty sand beds. A 1m-thick blanket is provided for silt, silty clay, or clay of low plasticity or in conditions where the underlying rocks are of a type known to be excessively susceptible to weathering. The blanket layer is generally composed of well-graded sandy gravel or crushed rock with specified distributions of size and curvature. Mixtures of fines (metal, plastic, etc.) from industrial applications are used in specific proportions in some cases, as are certain other waste materials that conform to specified mechanical, chemical, and geometric requirements.

The subgrade is generally built up from a mixture of soil and stone fragments, cobbles, and waste materials, crushed brick, etc. The blanket and subgrade are built up at a slope of about 2:1. The entire embankment

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may rise to 6m with most ordinary kinds of materials used for the blanket and subgrade. In case the subgrade is thicker than 1m or so, usually a 30cm layer of compacted soil is provided for every 1m-3m of the subgrade thickness.

Q. What are 'GeoJute' and 'GeoGrids'? How does IR prevent soil erosion in the areas where track is laid?

Erosion of the soil around a track formation can be quite dangerous as the track may subside or warp and move. In many cases IR simply encourages the local shrubby vegetation to grow in the areas near the track to stem the erosion. Where severe erosion is a problem, 'GeoJute' has been used. This is an ecologically safe material made of jute yarn with a coarse open mesh structure. This is placed on the affected portions of the embankment or cutting after removing clods, large stones, etc., and appropriate scrubby vegetation is seeded in the area. The jute yarn is biodegradable and disappears after a while, but by that time the vegetation has had a chance to take root and grow firmly in the protected soil.

In rare cases where vegetative root growth is thought to be insufficient to stem the erosion of the soil, a synthetic root matrix reinforcement system may be used. Known as 'GeoGrids', these flexible, synthetic meshes of simply extruded, unoriented and unstretched polymer materials are placed in the top layer of the soil to provide erosion resistance both by its own presence and by strengthening the root matrix of the local vegetation.

These GeoGrid polymers are non-biodegradable, and quite stable, resisting ultraviolet exposure and tolerant of very high and low temperatures. Boulder retention in some places is augmented by the deployment of bi-axially oriented GeoGrid meshes to anchor medium to large boulders. In a few cases, IR has also resorted to 'hydroseeding', involving the sprinkling of seeds of fast-growing grasses and scrub vegetation with specially formulated mulch and fertilizer mixtures.

Self-stabilizing Track Konkan Railway has developed something they call self-stabilising track, which aims to reduce or even eliminate the problem of ballast being de-compacted and dispersing under the action of vibrations set up by moving trains.

The ballast in this system is laid on the track bed pre-compacted with constraining 'cages' that hold large amounts of ballast together. These

cages or ballast elements are of several modular shapes, 'L' or 'T', etc., and are placed in interlocking ways on the track bed. The effect is not only to prevent the ballast from spreading under the action of vibrations, but to improve ride quality by changing the vibration characteristics since the inertial mass responding to the impact from the train is larger. A thin sheet of rubber or polyethylene between the sleepers and the top of the track bed further modifies the vibration characteristics. The ballast elements are constructed of such a shape that the vibrations tend to wedge them more firmly together. The expectation is that ballast maintenance will be much reduced for such tracks.

Q. What tolerances of gauge does IR permit?

Broad Gauge Deviations allowed from nominal gauge: -5mm to +3mm on straights and curves over 350m radius, and up to +10mm on curves sharper than 350m radius. (The older specifications were: On straight sections, a deviation of +/- 6mm; and on curves a deviation of up to +20mm/-6mm.) High-speed sections (130+ km/h) have tighter tolerances of +/- 2mm.

Q. What are the nets one sees on rockfaces or hillsides abutting railway lines in some areas?

In areas where rock falls or landslides are common, IR uses meshes or nets fixed to the rockfaces or the hillsides -- these are 'stitched' to the hillside at frequent intervals. They act to trap and stop, or slow down falling or sliding rocks and boulders so that they either do not fall all the way down, or lose their kinetic energy and fall without infringing the tracks.

Generally the nets are made of polypropylene ropes of 10mm-16mm diameter with high thermal, abrasion, and ultraviolet resistance. The mesh size is from 100mm to 300mm depending on the area, and the typical size of the fractured or falling rocks. These are appropriate for retaining and slowing small to medium sized boulders and the mesh strength is about 6-8 tons / m2. In some areas steel nets made of high-strength galvanized steel wire ropes are used. These ropes have a breaking strength of 4 tons and provide a mesh strength of 13-14 tons / m2 to retain large boulders. These have a design life of over 20 years.

Q. What is the 'Raksha Dhaga'? What other methods does IR use to warn of landslides and rockfalls?

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It consists of a wire attached to sensors which can be tripped when the wire is moved excessively or snapped by a falling rock. The sensors when tripped activate lights and hooters 0.5km away so that approaching trains can safely stop before the location of the landslide. These are used in several stretches on the KR route in cuttings and in unlined tunnels.

In addition, KR has pioneered the use of electronic inclinometers to detect earth slippages in areas prone to landslides, connected to a similar warning system as in the Raksha Dhaga.

Maintenance

Q. How is track maintained?

Permanent way maintenance is largely done by gangs consisting of gangmen under the supervision of a gangmate. The gang goes down its assigned section of track (the gang beat or beat section), inspecting track and performing normal routine maintenance. A patrolman may be separately deputed to perform visual inspections along the length of a section of track by walking alongside it (two patrolmen in ghat or jungle areas). Typically the patrol may cover 6km - 10km of track.

The schedule and track sections to be monitored by gangmen and patrolmen is specified in a Patrol Chart prepared by the Divisional Engineer. This chart also indicates when and where the drivers of trains running to schedule may expect to meet gangmen. Patrolmen and gangs carry Patrol Books in which they record the status of the track and any maintenance they perform on it.

The gang is equipped to deal with minor problems such as fixing small deviations in gauge or elevation of the rails, rearranging ballast, etc. If problems are discovered with the permanent way that cannot readily be fixed by the gang, the details are reported to the station master of one of the adjacent block stations, and temporary engineering speed restrictions are put in place for the track. Trains going through that section are then subject to caution orders issued by the stations at either end.

A bigger maintenance of way crew with appropriate tools and machinery then works on repairing the track while it is protected by being restricted. In some cases traffic on the line may have to be completely stopped. Replacing ballast or sleepers, adjusting the rail profile by grinding, joint lubrication, rail creep adjustment, replacing short sections of damaged

rail, welding rails, etc., are some of the other maintenance tasks that come up.

The regular patrolling of track is very important in order to maintain safe conditions for trains. If a patrolman or gang is unaccountedly late or if a patrolman misses his beat for some reason, caution orders are usually issued advising drivers to be alert for track defects and restricting trains on the affected sections of track to 40km/h (daytime, clear visibility) or 15km/h (night, bad visibility).

The permanent way inspector (PWI) for a division has ultimate responsibility for the condition of the permanent way under his jurisdiction. The PWI and his staff undertake separate regular inspection tours of the various lines, often in a motor trolley or inspection car. (In the past manually pushed trolleys were used quite often, but their use is declining now.)

A few track maintenance machines are in use, for instance tie tamping machines, ballast cleaning machines, etc.

Q. What is 'beater packing'? What is included in the maintenance carried out by gangs commonly seen on the tracks?

The most common system of routine manual (non-mechanized) track maintenance is known as through packing or beater packing (from the name of the tool used for packing ballast, a 'beater'). This includes the following steps:

1. Opening of the road : ballast is unpacked, fittings and fastenings of the rails loosened

2. Examination of track : Rails, sleepers, fastenings are carefully examined for signs of wear, corrosion, rust, dust and dirt, etc. Wire brushes are used for cleaning; jimcrows and other tools to rectify minor kinks or other defects. Sleepers are examined for signs of splitting or decay. Minor repairs such as replacement of fastenings, rail lubrication, etc., are performed.

3. Squaring of sleepers : Sleeper hammers are used to adjust sleepers to the proper position.

4. Slewing of track to fix the alignment of the rails. 5. Gauging : the gauge between the rails is carefully measured and

adjusted as necessary. 6. Sleeper packing : Each sleeper is uniformly and firmly packed so the

rails are the correct relative levels and to ensure the sleepers have no

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voids between themselves and the trackbed. This is where 'beaters' are used. These are long rod-like tools with an end used to pack the ballast. The beater is held by the hands and raised to about chest level and then plunged downwards to pack the ballast.

7. Re-packing of joint sleepers 8. Boxing the ballast section and clean-up.

Another system of manual ballast packing called 'measured shovel packing' used to be common but is now not in use.

In addition to ballast packing, gangs perform a variety of other cleaning and maintenance jobs, such as maintaining drainage, adjusting cess level (too high affects drainage, too low results in ballast spread and wastage), removing weeds and stones, etc.

Crews also pick up slack in the track. Slack refers to the condition where there is insufficient ballast or a gap developing between the track and the trackbed, or subsidence of the track, because of a yield formation in high banks and cuttings, at approaches to bridges, on badly aligned curves, where ballast is poorly laid or insufficient, or where there are drainage defects causing subsidence problems. Slack is picked up by opening the track and repacking the ballast.

Track Defects

An explanation of track defects in general is beyond the scope of these pages. Please consult any current reference book on permanent way technology.

Q. What is 'through' or 'scattered' renewal?

Complete Track Renewal (CTR) refers to the most thorough track replacement regime where rails, sleepers, etc., are fully replaced. Through Rail Renewal (TRR) refers to the replacement of rails in a given section of track, while Through Sleeper Renewal (TSR) refers to the replacement of sleepers. Similarly, there are Through Turnout renewal (TTR), Through Fitting Renewal (TFR), Through Weld Renewal (TWR), and Through Bridge Timber Renewal (TBTR). Each of these has a more thorough ('primary') and less thorough ('secondary') versions, hence you see the acronyms like 'CTR(P)' for 'Complete Track Renewal - Primary', or 'TSR(S)' for 'Through Sleeper Renewal - Secondary. Additionally there are 'Casual' renewals, which refers to renewals of any kind that happen

not on a predetermined schedule but as determined based on patrolling and inspection of tracks, in small continuous stretches. Finally, 'Scattered' renewal (SR) refers to ad hoc replacements that happen at isolated points.

Q. Does IR use mechanized means for track laying and maintenance?

IR has used some track-laying equipment, but much track is still laid manually. A lot of track maintenance is also done manually, with a veritable army of gangmen that are out 'on the line' to inspect track and fix problems. There is, however, a big push to mechanize track maintenance -- the target being complete mechanization by 2012.

Tie tamping machines are common: Unimat models (by Plasser) tamp one sleeper at a time and can pack sleepers on normal track and turnout; Duomat models tamp two sleepers at a time on normal track. CSM is another tie tamper used by IR; it has a cab that moves continuously while the tamping machine itself starts and stops over alteranate sleepers to tamp them two at a time -- this reduces driver discomfort. CSM tampers are the most common ones used by IR today. [6/04] A 'Tamping Express' machine that tamps three sleepers at a time is being tried out.

Self-propelled ballast cleaning machines have been tried in a few places but remain rare. Ultrasonic rail testing cars, rail geometry test equipment, etc. are also used on occasion, but the main method of rail inspection remains visual inspection by gangmen.

Track laying and relaying by machines is increasingly common. Plasser brand machines are seen quite often. These include the 'PQRS' or Plasser Quick Relaying System which consists of self-propelled portal cranes, which travel on a wider gauge, called auxiliary track, laid temporarily, outside the track to be renewed. Their capacity for track renewal is about 400m per effective traffic block hour. The manufacturers are Plasser and Theurer, BEML, and Simplex.

'TRT' or Track Relaying Train machines (also sometimes Track Renewal Train), capable of continuously relaying track at a few hundred meters an hour are also seen (as of 2004 there were at least four of these, perhaps more). These are made by 'M/S Harsco Track Tech' (earlier 'Fairmont Tamper' and still earlier, called 'Tamper Corporation') of USA. (One machine of this type was purchased initially from Russia, but that was a

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one-off purchase.) The 'T-28' is a point and crossing renewing machine made by Ameca, Italy, used for re-laying track at turnouts and points.

BEML has recently been supplying IR with BG track-laying machines. These machines can remove old rails, and lay new BG track (including concrete sleepers), assembling the rails and sleepers into panels before laying the track.

A machine consists of two large vertical frames which are connected by a bridge. The bridge can be moved up and down between the side frames. A diesel engine and hydraulic pumps are installed on the bridge. The vertical frames rest and move on rails of an auxiliary track of 3.4m gauge. The wheel base is about 2.4m. It weighs about 12t, and can move at about 14km/h.

The machine can lift sleepers and track up to 9t. Panel lifting is accomplished by the use of four independently controlled hydraulic scissors mechanisms. Rails and sleepers can also be moved laterally through hydraulic positioners. The equipment attached to the bottom of the bridge is connected via a turntable, allowing for rotational movement of the loads being lifted. Sleepers are gripped by hydraulically operated angle grippers.

For track inspection and monitoring by mechanical means, IR also now uses laser-based contactless track-recording cars for measuring rail corrugation. Portable accelerometers and optical rail profile measurement systems are in use in trials in some places with large scale use expected in the next few years.

Q. What is included in the 3-tier maintenance regime?

The three-tier system divides responsibilities for track maintenance as follows:

1. On-Track Machines (OMU). Mechanized maintenance (see above) including systematic tamping, intermediate tamping, shoulder ballast cleaning, ballast profiling and redistribution, track stabilization, and periodic deep screening of ballast.

2. Mobile Maintenance Units (MMU). These are of two types. MMU-I refer to the permanent way units that are assigned to deal with spot tamping, in-situ rail welding, casual renewal and repairs, overhaul of Level

Crossings, glued joint replacement, and machining of rails including cutting, drilling, grinding and chamfering. Normally there is one MMU-I unit for each Permanent Way Inspector's office. MMU-II refers to the units specially assigned for reconditioning turnouts, switches, joints and other such intricate trackwork.

3. Sectional Gangs. These are permanent way gangs that handle patrolling (including keyman's daily patrols, hot and cold weather patrols, and monsoon patrols), and watching vulnerable locations, bridges, turnouts, switch expansion joints, level crossing approaches, etc. In addition these teams handle minor maintenance including temporary repairs, lubrication of elastic rail clips (ERC) and joints, changing rubber pads, liners, and clips, minor cess repairs, cleaning drains, boxing ballast, manual adjustments of loops and creep / gap adjustments, cleaning crib ballast and handling other drainage issues, deweeding, removing boulders and other debris, and pre- and post-tamping attention. Periodically, the sectional gangs also carry out maintenance such as picking up slack in the permanent way.

Q. Sometimes the sides of rails appear to be painted. Why is this done?

Normally, rails do not need to be painted as the expected life span resulting from the effects of wheel wear and fatigue is such that corrosion is not a significant problem. In some areas, however, corrosion of rails, especially on the inside of the rail foot below the liners, or on the sides, can be quite severe, and may result in the need for premature renewal of the tracks even if the rails are otherwise not worn or fatigued by the traffic conditions. The problem is worse when the spots where the corrosion makes the rails weak move out of the sleeper seats during activities like track destressing.

Corrosion happens in coastal areas and regions such as the Sambhar Lake area where there is high salinity. Damp tunnels are also places where corrosion can be higher than normal. In addition, since IR currently uses direct discharge toilets for passenger trains, corrosion resulting from toilet waste is a significant problem on some lines, and especially at approaches to major stations where many busy lines converge.

To prevent such corrosion and to increase the life of the rails, IR practice is to paint the rails on the sides and on the foot in affected areas.

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