Post on 30-May-2018
8/14/2019 What is Railway
1/12
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)
8/14/2019 What is Railway
2/12
Railway Engineering6th semester
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.
A
commo
dity
isagoodwh
ichis:
usuallyprodu
cedand/ors
oldbymany
differentcompan
ies
uniform
inqualitybetwee
ncompanies
thatproduce/sellit
A commuter is a person who
makes the journey from
home to work and back every
working day using some form
of transportation system
8/14/2019 What is Railway
3/12
Railway Engineering6th semester
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)
8/14/2019 What is Railway
4/12
Railway Engineering6th semester
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.
8/14/2019 What is Railway
5/12
Railway Engineering6th semester
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
8/14/2019 What is Railway
6/12
Railway Engineering6th semester
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.
8/14/2019 What is Railway
7/12
Railway Engineering6th semester
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.
8/14/2019 What is Railway
8/12
Railway Engineering6th semester
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.
8/14/2019 What is Railway
9/12
Railway Engineering6th semester
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:
8/14/2019 What is Railway
10/12
Railway Engineering6th semester
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
8/14/2019 What is Railway
11/12
Railway Engineering6th semester
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
8/14/2019 What is Railway
12/12
Railway Engineering6th semester
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.