Construction of Railway Tracks

8/11/2019 Construction of Railway Tracks

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Railway Track | 4/17/2014 1

onstruction of Railway tracks

Railway or Permanent-way is the combination of rails,

sleepers, fittings, ballast etc. The railway track is a dynamic system of interacting components

that distributes the loads and provide a smooth, stable running surface for rail vehicles. This

system must provide vertical,lateral and longitudinal stability.

Tr ack Design and construction:1) Its desirable attributes are,

Balance Stiffness and Resiliency

Resistance to permanent deformation

Stability

Adjustability

2) It has apparently a simple structure, has changed little.

3) Loading must be reduced through the rail, ties, ballast and sub-ballast to within the

bearing capacity of the underlying subgrade.

Track Function:1) Guide Vehicles

2) Provide a high vehicle ride quality

3) Withstand and distribute loading i.e,

Static (36 tons/axle) or (36000 lbs/wheel)

Plus dyanamic

Di fferent methods used to design tr ack and Cr oss-section:1) Trial and Error

2) Emperical (based on trial and error)

3) Emperical/Rational (by measuring loading and material properties)


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4) Rational (Stress/Strain Analysis and measurments..

The Trackbed is subjected to a variety of loads and stresses:

Dead Loads Live Loads Dynamic Loads Centrifugal Loads Lateral Loads (hunting and

noising of wheels) Thermal Loads (Continuosuly

welded rail) Longitudinal Loads (wave action)

El ements of Rai lway Tr acks:

A railway track is a combinationof:

1. Formation

2. Ballast3. Sleepers

4. Rails

5. Fastenings


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Ballast is a layer of broken stone, gravel, or any other suitable material placed under and

around the sleepers for distributing the load from the sleepers to the formation.

The Ballast should be designed and installed having thickness ranges from (8 inch to 12 inch)

and should be sufficient to support the track loads and at minimum should match the section of

the adjacent track.

Tr ack Sub-stru ctur e design

Here we will discuss the track sub-structure components i.e, the Ballest and Sub-ballast

sections. Single and multiple track construction will be addressed, as will track with super-

elevation. The following figures are shown:

1) Typical section Track Sub-structure


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2) Single Track Super-elevated

3) Multiple Track, Tangent


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Ball ast Section

Ballast Section Depth (BDD)

a) The ballast section is the upper portion of the track substructure section and isconstructed of the material discussed below.

b) For a single track construction, the measurement BDD is made under the line rail in thetangent track or under inside rail in curved track and is made with respect to the top ofthe sub-ballast at the centre line of the track. On tangent multiple track construction,the measurement is made under the rail which is towards the crown of the sub-ballastsection. On curved multiple track construction, the measurement is made under the railto the inside of the curve.

c) A value for BDDof a minimum of 12 inches is recommended for Standerd Gageconstruction in main track service or as defined by the individual railway companystanderds.

Ballast Section Shoulder Width (BSW)

a) The Ballast section shoulder width should be proportional to the track relationshipused and should provide additional lateral strength to thr track.

b) The measurement is made from the end of the cross-tie to the point of beginning ofthe ballast Side Slope (BSS) and is made in the plane of the top of cross-tie.

c) A value for BSW of not less than 12 inches is reccommended for the Standerd Gageconstruction of continuous welded rail in main track service or as may be designedby the individual company standerds.

Side Slopes (BSS)

a) The side slope run component of the ballast section is proportioned to provide confiningpressure to that part of the Ballast section expected to transmit the vertical load fromthe bottom of the cross-tie to the top of the sub-ballast.

b) The BSS run component is measured in the plane of the top of the cross-tie, and the risecomponent is measured perpendicular o the run component.

c) A BSS value of 2:1 is commonly used.


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Types of M ater ial used as Ball ast:

A variety of materials may be processed into railroad ballast. The following general

classification and accompanying definitions list the most common materials. Detial examination

of individual materials should be made to determine the specific mineralogical composition.

a) Granite is a plutonic rock having an even texture and consisting chiefly of feldspar and

quartz.

Definition: A plutonic rock is a rock formed at considerable depth by chemical alteration. It

is characteristically medium to coarse grained, or granitoid texture.

b)

Traprock is any dark-colored fine grained non-granitic hypabyssal or extrusive rock.

Definition: Hypabyssal-Pertaining to igneous intrusion or to the rock of that intrusion whose

depth is intermediate between that of plutonic and the surface.

c) Carbonate rocks are sedimentary rocks consisting primarily of carbonate materials such

as Limestones and Dolomite.

d)

Quartzite is a granoblastic metamorphic rock consisting mainly of quartz and formed bythe recrystallization of sandstone by either regional or thermal metamorphism.

Quartzite may also be very hard but un-metamorphosed sandstone consisting chiefly of

quartz grains with secondary silica that the rocks break across or through the grains

rather than around them.

GeoGri d Defi ni tion:

A geogrig is defined as a geosynthetic formed by a regular network of tensile elementswith apertures of sufficient size to allow strike-through of surrounding soil, rock or othergeotechnical materials. Geogrids are principally used for reinforcement purpose, butunder some circumstances. They can also provide effective separation between two soiland granular fill layers.


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Significance and Use:

Some of the benifits of GeoGrid Reinforcement with in the Roadbed section include thefollowing:

1) Increase Ballast life (life cycle cost saving).2) Reduced Roadbed Thickness (Initial cost saving).3) Reduced track deflection resulting in less wear and tear of the mechanical components

of the rail track.4) Maintenance of good drainage within the roadbed section.5) Smoother transitions between areas with different subgrade strengths

Application Locations of GeoGrids:

GeoGrids is tends to be used in one or both of the two (2) main locations within the roadbedsections i.e,

1) At the bottom of, or within the ballast.This provides direct ballast reinforcement

and thereby reduces the rate of track settlement, it therefore increases the length of

maintenance cycle . This approach is generally favored when the roadbed is founded on

a relatively firm subgrade.


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2) At the bottom of the sub-ballast, directly on theexisting or preparedsubgrade

This is done in order to increase the bearing capacity of the track foundation.This approach is generally favored when the roadbed is founded on a relatively softsubgrade.

Sleepers:Sleeper is transverse support for a railway to give stiffness to it.


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Diffrerent types of sleepers are used in railway tracks:

1) Concrete Sleepers:

Concrete ties are rapidly gaining acceptance for heavyhaul mainline use They are made of pre-stressed concretecontaining reinforcementsteel wires. The concrete cross-tie wieghs about 600 lbs vs 200 lbs timber track tie.Theconcrete ties utilizes a specialized pad between the base of the rail and plate to cushionand absorb the load as well as to better fasten the rail to the tie.

2) Steel Sleepers:Steel Sleepers are often relegated to specialized plant locations or areas not favorable


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to the use of either Timber or Concrete such as tunnels with limited headway clearance. Theyhave also been utilized in heavy curvature prone to gage widening. However they have notgained wide acceptance due to problem associated with shunting of signal current flow toground. Some lighter models have also experienced problem with fatigue cracking.

3) Wood Sleepers:Softwood timber is not more resistant than hardwood, but does not offer a

reisitant of a hardwood tie to tie plate cutting, gauge spreading, and spike hole enlagement.Softwood ties are also not as effective in transmitting the loads to the ballast section as thehardwood tie. These are mostly used in open deck bridges.

Rails Joints:There are three (3) basic types of joints used in railway Track:

1) Standerd

Standerd joint bars connect

two rails of the same weight and section. They

are typically 24 in length with 4 -bolt holes for

the smaller rail sections or 36 in length with

6-bolt holes for the larger section. Alternate


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holes are elliptical in punching to accommodate the oval necked track bolt.

2) Compromise

It connects two rails ofdifferent weight or sections together. Theyare constructed such that the bars align therunning surface and gage sides of differentrails sections.

3) Insulated

These are used in tracks havingtrack circuits. They prevent the Electricalcurrent from flowing between the ends oftwo adjacent rails, thereby creating a trackcircuit section. Insulated joints use aninsulating end post between rail ends toprevent the rail from shorting out. Theseare of 3 types:

1) Continuous2) Non-continuous3) Bonded

Fastening:A rail fastening system is a means of fixing rails to railroad ties or sleepers. The terms railanchors, tie plates, chairs and track fasteners are used to refer to parts or all of a rail fasteningsystem. Various types of fastening have been used over the years.
http://en.wikipedia.org/wiki/Rail_profilehttp://en.wikipedia.org/wiki/Railroad_tieshttp://en.wikipedia.org/wiki/Railroad_tieshttp://en.wikipedia.org/wiki/Rail_profile


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1) Rail Spikes:

A rail spike (also known as a cut

spike or crampon) is a large nail with an

offset head that is used to secure rails and

base plates to railroad ties in the track.

2) Skrew Spikes:

A screw spike , rail screw (or lag

bolt) is a large (about 6" length, slightly under 1"

diameter) metal screw used to fix a tie plate or

fasten rail. Screw spikes are fixed into a hole

bored in the sleeper. The screw spike has a

higher cost to manufacture than the rail spike

but has the advantage of greater fixing power,

approximately twice that of a rail spike, and can

be used in combination with spring washers.

3) Spring Spikes :

Spring spikes, (or elastic rail

spikes ) are used with flat-bottomed rail,

baseplates and wooden sleepers; the

spring spike holds the rail down and

prevents tipping, and also secures the

baseplate to the sleeper.
http://en.wikipedia.org/wiki/Nail_(engineering)http://en.wikipedia.org/wiki/Railroad_tiehttp://en.wikipedia.org/wiki/Lag_bolthttp://en.wikipedia.org/wiki/Lag_bolthttp://en.wikipedia.org/wiki/Spring_washerhttp://en.wikipedia.org/wiki/Spring_washerhttp://en.wikipedia.org/wiki/Lag_bolthttp://en.wikipedia.org/wiki/Lag_bolthttp://en.wikipedia.org/wiki/Railroad_tiehttp://en.wikipedia.org/wiki/Nail_(engineering)


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4) Chairs:

The railway chairs , made of cast iron, used to fix and support cast-iron rails at the ends. They

were also used to join the adjacent rails .

M ain tenance and Renewal Process Of Rail way Station:


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Reference Sites:

1) www.arema.org

(American Railway Engineering and Maintanence of way Association)

2) FRA

(Federal Railroad Association)
http://www.arema.org/http://www.arema.org/http://www.arema.org/

Documents

Construction of Railway Tracks