What is Railway

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Railway Engineering6th semester

Introduction to Railway Engineering(Lecture # 1)

Subject : Railway Engineering

Department of Transportation Engineering and Management,

UET Lahore.

What is railway?A railway can be defined as an engineered structure consisting of two metals

guiding rail on which cars are either self propelled or pulled by a locomotive.

What is railway engineering?Branch of Transportation Engineering involved in the planning, design,

construction, operation and maintenance of railway land facilities used for the

movement of people and goods serving the social and economic needs of

contemporary society and its successors.

Why Railways are built?There could be several reasons, some might be:

Military Purpose (strategic conditions)

Linking of trade centres

Connecting port with interior of country

Shortening existing route

Laying of a Branch Line

ABCC

ABCD

______ ACB (Existing Line)

-------- ACB (Proposed shorte

line)

______ ACB (Main Line)

-------- ACD (Proposed Branch

Line)


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Place of Railways in SocietyAt one point in time, railroads were most important (In terms of usage) part of

transportation system, because they were the only ones which made the mass

movement of people and goods possible. Today railway industry is famous for its

use in transport of freight.

Because of their higher weights and increased volumes, bulk products like coal, iron

ore, wheat, building material, etc. railways as the mode of their transportation is

desirable as compared to other modes.

Comparison Among Modes (Freight Transport)

Motor Truck: Rapid movement of freight over short distances and flexibility of

movement in urban areas.

Airlines: Rapid service for passengers, mail and small shipments of lightweight,

valuable commodities where speed is a controlling factor

Waterways: Bulk freight is transported at low cost but slow speed.

Pipelines: Direct, low cost and dependable movement of petroleum and gas.

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Railroads: Provide rapid, economical and dependable movement for all types of

commodities especially bulk freight. Mass commutation is also possible through

railways (interchangeably called as railroads)

Right of WayA railway right of way, abbreviated as ROW or R/W, is the land upon which theroadbed and other necessary facilities are constructed.

On single track railways, the width of R/W is usually measured at right angles to the

centre line of track and from the centerline to the edge of the railways property, a

boundary known as right of way line. On a multiple track railway,

the centre line of the R/W may coincide with the centerline of one

of the tracks or it may come midway between the tracks.

Width of Right of Way

Common widths are 50, 60, 80, 100, 200, or even 400. Withinstation limits the width is increased to incorporate necessary

structures, facilities and tracks.

What should be considered while acquiring Right of Way?1. Depths of cuts and fills

2. Slopes

3. Side ditches

4. Erosive action of wind and water, etc.

5. Future double tracking

6. Price of land, as the land value increases after construction of railway facility.

Increasing or acquiring R/W afterwards could be more costly.

Elements of railway track and theirfunctions (Lectures 2+3)

Subject : Railway Engineering

Department of Transportation Engineering and

Management, UET Lahore.

Roadbed

Ballast

Sleeper

Fastenings

Rails

PAK-WATCH

R/W is usually100 in Pakistan

Figure 1: Elements of Railway Track (figure not toscale)


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RoadbedA railway roadbed is a regular, prepared subgrade on which are laid the ballast

section, ties and rails.

Purpose of subgrade

1. Weights of tracks + ballast + train loadings are supported as uniformly aspossible and transmitted with diminishing uniform pressures to the

supporting natural ground beneath.

2. Drainage is facilitated.

3. Smooth, regular surface is provided on which the ballast section and track

structure can be laid.

Design of roadbed section

Three important factors have to be considered:

1. Width of subgrade (or base of cut)

2. Depth of cut or fill3. Side slopes of the cut or fill

Width of roadbed

It is determined in part by width of ballast section which depends on several

variables like subgrade and ballast material, weather, size of ties, weight of

rail, volume and speed of traffic and axle loadings.

Design of ballast section & width of subgrade is based on expected traffic at

least 10 to 15 years in future.

The cost of extra width at the time of construction should be balanced

against estimated future cost of roadbed widening.

Separate standards of roadbed & ballast are used for mainline and branchline.

Road bed shoulders should extent a minimum of 18 beyond the toe of

ballast slope to give adequate support to ballast section.

More widening of subgrade is required where soils are susceptible to wind /

water erosion.

In case of settlement, final top subgrade width must be maintained.

Otherwise with successive ballast layers (also called as lifts) to hold the

established gradient, top of fill becomes too narrow for its height and for the

width of ballast section.

The most important factor affecting width of cuts is side ditches. Base width of 3 6 with side slopes of 1:1 are standards in common use for

width of cuts.

If gradient is steep, shoulder must be protected against erosion.

Depth of Fill (Embankment)

Allowance for settlement & erosion must be given.

High water levels must be considered.


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Side Slopes

Depends primarily upon shearing strength & angle

of repose of the materials forming the slope.

A slope of 1 12 : 1 is commonly used in railway

design for both cuts and fills and gives reasonable

stability for most materials. Sands / Clays may require 2 : 1 or even 3 : 1

Solid rock cuts may stand on 12: 1 or 14 : 1

A final decision on rate of slope must depend on type of soil used rather than

on rule of thumb.

A slope of 2 : 1 is approximately one third longer than 1 12 : 1 and receives,

approx. one third more rainfall. Therefore effects of erosion must be

considered while deciding whether to make slope wider or flatter.

Slope Protection

Different options exist, some are:

1. Paving:

To pave means to make hard, durable and permanent.

It gives pleasing appearance. There are options of stone

paving, asphalt paving, etc. Decision must be made

according to budget.

2. Rip Rap:

Loose placement of stones along slope with toe wall.

Protects saturated fills along rivers and lakes.

Grouting between stones could be used for greater stability.

3. Planting:

Choice of plantings is determined by conditions of local soil, climate and rainfall.

Native plants are likely to give best results.

4. Cinder Blankets:

Used for clay embankments.

5. Retaining Walls:

Provided when angle of slope is considerably greater than angle of repose of slopematerials.

Figure 2: Asphalt Paving


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Roadbed Materials

Functions of soils

Soils have a dual function for roadbed. 1) Soils constitute the foundation on

which railways are constructed. 2) Soils are also the materials of which the

roadbed is constructed. An engineer cant always select soils entirely by his own choice because a

railway track is hundreds of miles long and a variety of soils are encountered

in the field. Proper knowledge of soils & their functions can help creating a

stable and purpose fulfilling track. This knowledge is primarily based on

classification of soils and their properties.

Testing of Soils for Selection

There are many tests related to soils which help in determining their behavior in

field.

1. Classification by Grain SizeSoil Type Grain Size

(mm)

Gravel Coarser than 2

mm

Coarse

Sand

2 0.6

Medium

Sand

0.6 0.2

Fine Sand 0.2 0.06

Silt 0.06 0.002

Clay 0.002mm and

finer

Uniformity coefficient = Cu =D60D10

The uniformity coefficient is defined as a ratio: the size at which 60 percent (by

weight) of a sample passes through a sieve (in other words 60 percent of the

sample is finer than a given size) divided by the size at which 10 percent of the

same sample (by weight) passes through a sieve (10 percent is finer than a given

size). A Cu of 1 indicates all the particles are the same size. As the number goes up

the size differentiation becomes greater and hence sample becomes less uniform.


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2. Atterberg Limits

It compares the differences in physical properties of clays at various water

contents

Plastic limit Pw is that lowest water content at which the soil begins to

crumble when rolled into threads.

Liquid limit Lw is that highest water content at which the soil will not flowunder standard conditions.

Some highway departments prohibit soils as fill materials having a Lw greater

than 65%

With consistency limits, we are able to know about the swelling and shrinking

potential of clays & silts.

Other tests include specific gravity, moisture content and shearing

strength.

Effect of Soil Properties On Roadbed / Subgrade

Properties of good roadbed materials

To fulfill the functions of subgrade, the greatest uniformity and permanency is

obtained when subgrade material is free of excess moisture and has physicalcharacteristics providing high internal friction, high cohesion, and density, low

compressibility, low capillarity and low elasticity.

Why High Internal Friction and Cohesion?

To hold the soil firmly in place Soil with less cohesion, such as wet sand , is likely to slump and slide in

addition to being susceptible to surface erosion.


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Why High Density?

A dense soil tends to exclude moisture since the volume is largely filled with

soil particles and little room is left for moisture to intrude

Why low compressibility?

A highly compressible soil is slow in consolidating. If not fully compacted atthe beginning, it continues to compress under traffic, causing the top of

subgrade to settle.

Why low elasticity?

The unfavourable reaction of compressibility is intensified if the soil is

highly elastic.

The compressed soil rebounds when the load is removed, and the process

of consolidation is prolonged.

Adverse Properties

Tendency to flow or run because of rounded shapes of sand & silts. Flowoccurs due to low internal friction and cohesion.

Swelling and frost action.

Lateral flow under pressure

Use of soils Gravel is the only natural soil which does not require an admixture to make it

suitable.

Theoretically ideal soil is one in which several constituents are equally

proportioned. Greater percentage of gravel is desirable due to its hardness

and structural strength. To this should be added sand to bed larger gravelparticles, silt to act as filler & clay to fill remaining voids and provide a water

film for cohesion.

Soil Proportioning

First Method

Bring from scattered pits the desired soils in proper amounts and mix the several

types in spreading and compacting operation.

Second MethodEngineer may obtain helpful selection at pit. If several grades and soil types are

available in one or more pits, the loading and unloading can be performed to place

the individual soils in proper relation to each other in fill.


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Control TestsStandard tests are done on actual construction samples and curves, charts & other

guides are provided, against which to measure & obtain the desired degree of

compaction. These tests are

1. Compaction Test2. Moisture Content for use in compaction test.

Inspection Tests1. These tests are done to insure that the standards established by the control

tests are being secured. These tests are:

2. Dry density test to determine adequacy of compaction

3. Soil-Volume Relations determination of unit weights before and after

excavation to establish change in volume.

4. Moisture-density relations amount of water required per unit of borrow

material to bring the moisture content of borrow material upto that of

compacted material.

Drainage

What is Track Drainage?

Drainage is defined as interception, collection and disposal of water away

from track.

If you intercept someone or something that is travelling from one place

to another, you stop them before they get to their destination You have to intercept the evil water before it reaches its destination which

is your very own railway formation.

Sources of Water Entering Track

Why Drainage is so important to study?

Because:


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There is scarcely any item of maintenance cost which is not increased by

effects of poor drainage.

A poorly drained subgrade permits cinders, stone dust and dirt to accumulate

in and foul the ballast, leading to pumping joints.

Pumping joints cause excessive rail end batter, joint bar wear & tie

deterioration. Washing out of tracks, poor line surface of gauge, accumulation of ice &

snow, obstructing tracks in tunnels.

Drainage Types

Intercepting & diverting ground water

Containing and channeling streams

Disposing of rainwater and snow run-off

Tapping and draining water pockets and springs

Intercepting seepage and underground streams

Drying Saturated fills

Lowering water tables Drying the ballast section by draining water from under the ties

All these could be broadly classified into Surface Drainage and Subsurface

Drainage.

Surface Drainage

Most important factor in embankment design and maintenance

Generally, provision of 1 in 30 cross slope on top of formation towards cess,

side and catch water drains, culverts and bridges comes under this category.

Types of Surface Drainage

1. Side Drains

2. Catch Water Drains

Side Drains

Normally not needed for embankment

Required if blanket is below ground level due to height of embankment

In case of cuttings, properly designed side drains of required water carrying

capacity are to be provided

Catch Water Drains

Surface water flowing from top of hill slope towards the track is controlled by

provision of catch water drains

Providing side drains for the same purpose is not feasible

Catch water drains are provided running almost parallel to the track upto a

point where the water can be safely discharged off


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Discharge Capacity of Catch

Water Drains

Channel Capacity = Q=A V

Where,

Q=Channel capacity

A=Cross-sectional area

V=Flow velocity

The flow velocity could be assumed or

found from mannings formula as under,

V= 1.486n r23 s12

Where,

r=hydraulic radius= AWetted Perimeter

s=energy slope per foot of length

n=roughness coefficient

Gradients of ditch may be same as tracks but not less than 0.3% to makeditches self flushing & free of standing water. Too high gradient, giving

velocities of 5 10 per second leads to scouring.

Subsurface Drainage

Main objectives of sub surface drains are to lower the level of water table and

to intercept or drain out underground water


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The sub-surface drains may consist of perforated pipe or open jointed solid

pipe in a trench with backfill around it or it may simply be free draining

material in the trench without any pipe

The subsurface drains can also be provided with geotextile either along the

trench or around the pipe or both

Backfilling Backfilled with excavated soil and thoroughly compacted so as to stop

water directly percolating from backfill material around the pipe. See the above

figure on this page.

Use of Free draining materials in subsurface drains

When only free draining material is used in trench, the main drain may be

constructed without any pipe. The trench may be filled with material such as gravel

or stone aggregate free from organic and deleterious substances.

Types of Subsurface Drainage (Group Discussion on 5th March)

Boulder Drains

French Drains

Horizontal Drains in Cuttings

Failure of Railway Embankments

Read this topic from the book Roads, Railways, Bridges, Tunnels & Harbor

Dock Engineering by B.L Gupta.

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