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UNIT 1-RAILWAY
ENGINEERING
• sleepers, various types, spacing and density, ballasts.
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TRANSPORTATION ENGINEERING II
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Sleepers
• Rails have to withstand the heavy load from thelocomotives and the coaches
• In the absence of sleepers, the track would just
settle down.
• Hence the need of these transverse memberscalled sleepers
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Function of sleepers
• Holding rail in proper gauge and level
• Act as elastic medium
•
Support the rails firmly and evenly• Distribute the load transmitted from the from the
rolling stock over large area of ballast
• Provides stability to the permanent way
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Requirements of Sleepers
• They should be sufficiently strong to act as a beamunder loads
• The sleepers should be economical
•
They should maintain correct gauge• They should provide sufficient bearing area for the rail
• The sleepers should have sufficient weight for stability
• They should facilitate easy fixing and taking out of railswithout disturbing them.
• They should be able to resist impacts and vibrations ofmoving trains.
• They should be suitable for each type of ballast.
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Types of sleeper
Sleepers are of the following types:
1. Wooden Sleepers
2. Steel Sleepers3. Cast Iron Sleepers
4. RCC Sleepers
5. Prestressed concrete sleepers
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Wooden Sleepers
• The life of wooden sleeper depends on their abilityto resist wear, attack by white ants and quality oftimber used.
• Timbers commonly used in India for sleepers areSal, Teak, Deodar and Chirwood.
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Wooden Sleepers
• The standard sizes for different gauges:
• For B.G. – 2740 mm x 250 mm x 130 mm
• For M.G. – 1830 mm x 203 mm x 114 mm
• For N.G –
1520 mm x 150 mm x 100 mm
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Wooden Sleepers
Advantages:
• Easily available in all parts of India
•
Suitable for all types of ballast• Require less fastenings and simple in design
• Give less noisy track
• Absorb shocks and vibrations more than any othersleepers
• Best suited for track circuiting
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Wooden Sleepers
Disadvantages
• Life is less as compared to other sleeper types
•
Sleepers are subjected to wear, decay, attack bywhite ants, etc.
• Track laid over wooden sleepers is easily disturbed
• Maintenance cost is more as compared to other
sleepers.
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Steel Sleepers
• Consist of steel troughs made of 6mm thick steelsheets, with its both ends bent down to check therunning out of ballast.
• At the time of pressing of sleepers, an inward slopeof 1 in 20 on either side is provided to achieverequired tilt of rails.
• Standard length of these is 2680mm.
• Steel sleepers are of two types:
• Key type steel sleepers
• Clip and bolt type steel Sleepers
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Steel Sleepers
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Steel Sleepers
• Key Type Steel Sleepers
• Lugs or jaws are pressed out of metal and keys are usedfor holding the rails.
•Lugs are formed by forming the pressing out of themetal of the channel section.
• Loose jaw type is an improvement on pressed lug type.
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Steel Sleepers
• Clip and Bolt type Steel Sleepers
• Clips and bolts are used for holding the rails.
• Cracks are not developed in the sleepers as the holes for
the bolts are small and circular.• Requires four bolts and four clips for holding each rail.
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Steel sleepers
Advantages:
• Are light in weight and can be handled easily.
•
Require less fastenings• Life is more than the wooden sleepers
• Gauge can easily be maintained and adjusted
• Scrap value is more than the wooden sleepers.
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Steel Sleepers
Disadvantages
• Initial cost is more than steel sleepers
•
Cracks are developed at rail seat of these sleepers• Are not suitable for track circuiting
• Not suitable for all types of ballast
• Liable to corrosion
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Cast Iron Sleepers
• Are made of cast iron and extensively used in Indiaas compared to other countries
• Are of following types:
• Pot or bowl sleepers
• Plate sleeper
• Box sleeper
• CST-9 sleeper
• Duplex Sleeper
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Cast Iron Sleepers•
Pot or bowl sleepers• Pot sleepers consist of two bowls placed under each rail
and connected together by a tie bar.
• Total effective area of both the pots is 0.464m
• On top of each pot, a rail seat is provided to hold rails atan inward slope of I in 20
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Cast Iron Sleepers
• Plate Sleeper• Consist of two rectangular
plates of 864 mm x 305 mmin size with short sizeparallel to rail.
• Plates are provided rib inthe bottom to provide agrip in the ballast for lateralstability., held in position bytie-bar.
• It provides an effectivebearing area of 0.464 sq mper sleeper
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Cast Iron Sleeper
• Box sleeper
• Not in use these days
• Are similar to plate sleepers
• A box is provided at the top of each plate to hold therails.
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Railway Engineering
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Cast Iron Sleeper•
CST-9 Sleeper• Extensively used in Indian Railways since thirty years
• It is a combination of pot, plate and box sleeper
• Consists of a triangular inverted pot one on each side ofrail seat
• Rail seat is provided at the top to hold rails at 1 in 20inward slope.
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Cast Iron Sleeper
• Duplex Sleepers• These sleepers are used at rail
joints to prevent cantileveraction between two supports
of CST-9 sleepers.
• Consist of two plates each ofsize 850 mm x 750 mm.
•
Plates are placed with thelonger side parallel to the railsand are connected with a tie-bar.
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Cast Iron Sleeper
Advantages
• life of C.I sleepers is more
• Maintenance cost of these sleepers is less
• Gauge can easily be maintained and adjusted withthese sleepers
• Sleepers are more durable
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Cast Iron Sleeper
Disadvantages
• More ballast is required than other type of sleepers
• Number of fittings required is more
• Sleepers are liable to break
• Are not suitable for track circuiting
• Not suitable for all types of ballast
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R.C.C Sleepers
• Through type RCC sleepers
• Known as one piece or monoblock sleeper.
• Cracks develop on the tension side when stressed
• These cracks are very small and almost invisible but tendto enlarge with the repetition of impact loading, causingfailure
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R.C.C Sleepers
• Block and tie type RCC sleeper
• Consist of two RCC blocks connected by a metal tie ofinverted T section.
•These sleepers are not subjected to any degree ortensile stress.
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R.C.C Sleepers
Advantages
• Have long life, generally 40-60 years
• Free from natural decay and attacks by insects, etc
• These require less fittings
• Track circuiting is possible in these sleepers.
• Maintenance cost is low
• Provide more lateral and longitudinal rigidity ascompared to other sleepers.
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R.C.C Sleepers
Disadvantages
• Due to heavy weight, handling and transportationof these sleepers is difficult.
• If not handled properly, the chance of breaking ismore.
• Renewal of track laid with these sleepers is difficult
• The scrap value is nil.
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Prestressed Concrete Sleepers
• Nowadays extensively used in Indian Railways
• Have high initial cost but are very cheap in long runbecause of their long life
• High tension steel wires are used in the sleeper
• these sleepers are heavily damaged in case ofderailment or accident of trains.
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Sleeper Density
Sleeper density is the number of sleepers used perrail length on a track. The density of sleepersdepends upon the following factors:
• Axle load of train• Lateral thrust of locomotives
• Methods of providing rail joints
• Speed of train
•Type of ballast
• Type and section of rails.
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Sleeper density
• Since sleeper provides lateral stability to the track, so morethe number of sleeper more is the lateral stability.
• The number of sleepers, however, cannot be increasedindefinitely as a certain minimum spacing between sleepers
is required for packing of ballast.• Sleeper density is indicated by (n+x), where n is the length
of the rail in metres and x is the number of sleepers inexcess of n.
• In india, number of sleepers per rail length is n+3 to n+6
•
In India, sleeper density of 18 sleepers per rail length isprovided.
• All the sleepers are not provided at equal spacing. At rail joints, the sleepers are kept closer as compared to otherparts to the rail.
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BALLAST
Ballast is the granular material usually broken stoneor any other suitable material which is spread on thetop of railway formation and around the sleepers
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FUNCTIONS OF BALLAST
• To hold the sleepers in position and preventing thelateral and longitudinal movement.
• To distribute the axle load uniformly from sleepers
to a large area of formation.
• To provide an east means of maintaining thecorrect levels of the two rails in a track.
•
To drain rain water from the track.• To prevent the growth of weeds inside the track.
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CHARACTERISTICS OF GOOD
BALLAST• Should have sufficient strength to resist crushing under
heavy loads of moving trains.
• Should be durable enough to resist abrasion and weatheringaction.
• Should have rough and angular surface as to as providegood lateral and longitudinal stability to the sleepers.
• Should have good workability so that it can be easily spreadon formation.
• Should be cheaply available in sufficient quantity near or
along the track• Should allow for easy and quick drainage of track
• Should not have any chemical action on metal sleepers andrails.
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TYPES OF BALLAST
• Broken stone (granite, quartzite, trap)
• Gravel
• Sand
•
Coarse sand• Ashes or cinders (waste products from steam
locomotives)
• Kankar (nodules from which lime is prepared)
• Moorum (obtained by decomposition of laterite)
• Blast furnace slag
• Brick ballast
• Hardened clay and decomposed earth
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SIZE OF BALLAST
• Size of ballast used in railway track varies from19mm to 51mm.
• For wooden sleepers – 51 mm
•For steel sleepers
–38 mm
• For points and crossings – 25.4 mm
• The more the depth of ballast below the sleeper,more will be the load carrying capacity of the track.
• The depth of ballast remains uniform throughoutthe straight tracks, but on curves additional ballastis required to give the required super elevation.
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SIZE OF BALLAST
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QUANITITY OF BALLAST
• The quantity of ballast per metre tangent length is
• 1.036 cu.m. for broad gauge
• 0.071 cu.m. for metre gauge
• 0.053 cu.m. for narrow gauge
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