Geometric desing of railway track

2017

Mohit M. Jain

M.jain

3/18/2017

Geometric Design Of Railway Track

Geometric Desing of Railway Track Page 1

GUJARAT TECHNOLOGICAL UNIVERSITY

Chandkheda, Ahmedabad

A Project Report

On

“Geometric Design Of Railway Track”

Under subject of

RAILWAY, BRIDGE & TUNNEL ENGINEERING

(2160603)

Submitted by:

Mohit M. Jain

140420106025

Guided By:

Prof. Vishwa Mehta

(Faculty Guide)

Department of Civil Engineering

Sarvajanik College of Engineering &Technology,

Athwalines, Surat.


SARVAJANIK COLLEGE OF ENGINEERING & TECHNOLOGY,

ATHWALINES, SURAT.

CIVIL ENGINEERING DEPARTMENT

CERTIFICATE

Date: This is to certify that the Report entitled “ Geometric Design Of Railway Track” has been carried out by Jain Mohit(140420106025). Under my guidance in fulfilment of the Degree of B.E. in Civil Engineering (6

rd semester)

of Gujarat Technological University, Ahmadabad during the academic year 2015-16.

Prof. Vishwa Mehta Prof. Pratima Patel

(Faculty Guide) Associate Professor & Head,

Civil Engineering Department Civil Engineering Department

EXTERNAL EXAMINER


ACKNOWLEDGEMENT

Behind every success there are lot many efforts, but efforts are fruitful

due to hands making the passage smoother. We express our deep sense of

gratitude for hands, people extended to us during our work.

Research brings about dramatic changes in the traditional look out of

science & technology. It is continuous phenomenon under taken by one and

every throughout the world. It has widened our vision, opened newer avenues

and lightened the dark obscure facets of mysteries universe. The work depicted

in this thesis is a bucketful of contribution to the large ocean of research

occurring globally. As one flower makes no garland, this presentation would not

have taken shape without wholehearted encouragement and live involvement of

some generous souls.

We express sincere and heartfelt thanks to Dr.Vaishali Mungurwadi,

Principal, and Associate Professor Pratima Patil, (Head of Civil Engineering

Department), Sarvajanik College Of Engineering & Technology for giving us

an opportunity to undertake this research subject for study.

We express a deep sense of gratitude to my guide Prof. Vishwa Mehta, Civil

Engineering Department, Sarvajanik College Of Engineering & Technology

for her constructive support, constant encouragement, guidance and challenging

our efforts in the right direction without which this thesis would not have

attained the present form.


Contents

Chapter 1: Introduction .............................................................................................................. 5

1.1 Introduction ................................................................................................................. 5

Chapter 2: Necessity................................................................................................................... 6

2.1 Necessity ........................................................................................................................... 6

Chapter 3: GEOMETRIC CROSS SECTION ........................................................................... 6

3.1 CrossSection ..................................................................................................................... 6

Chapter 4: Gradients................................................................................................................... 8

4.1 Gradient............................................................................................................................. 8

4.2 Types of gradients ............................................................................................................. 8

4.2. (a) Ruling Gradient .......................................................................................................... 9

4.2. (b) Pusher or Helper Gradient ........................................................................................ 10

4.2. (c) Momentum gradient ................................................................................................. 10

4.2. (d) Gradients in station yards ......................................................................................... 11

4.2. (e) Grade Compensation on Curves ............................................................................... 12

Chapter 5: Curves ..................................................................................................................... 13

5.1 Curves ............................................................................................................................. 13

5.2 Maximum Degree of a Curve ......................................................................................... 13

Chapter 6: Superelevation ........................................................................................................ 14

6.1 Superelevation................................................................................................................. 14

6.2 Objective Of Providing Superelevation .......................................................................... 14

6.3 Centrifugal Force on a Curved Track ............................................................................. 14

6.4 Formula for Superelevation ............................................................................................ 16

6.5 Thumb Rules for Calculating Superelevation in the Field.............................................. 16

6.6 Types of Cant .................................................................................................................. 17

6.6.1 Equilibrium cant........................................................................................................... 17

6.6.2 Cant deficiency ( Cd ) .................................................................................................. 17

6.6.3 Cant excess ( Ce ) ........................................................................................................ 17

Chapter 7: Widening of Gauge on Curve ................................................................................. 18

7.1 Widening of Gauge on Curve .................................................................................... 18


Chapter 1: Introduction

1.1 Introduction

Geometric design for transportation facilities includes the design of

geometric cross sections, horizontal alignment, vertical alignment, intersections,

and various design details. These basic elements are common to all linear

facilities, such as roadways, railways, and airport runways and taxiways.

Although the details of design standards vary with the mode and the class of

facility, most of the issues involved in geometric design are similar for all

modes. In all cases, the goals of geometric design are to maximize the comfort,

safety, and economy of facilities, while minimizing their environmental

impacts. This chapter focuses on the fundamentals of geometric design, and

presents standards and examples from different modes.

The order of presentation of material in this chapter is to consider

geometric cross sections first, then vertical alignment, horizontal alignment,

super elevation , and various design details. For purposes of exposition, the

order of the topics is not very important. In a typical design project, on the other

hand, there is a definite order of tasks, in which the establishment of a tentative

horizontal centreline usually precedes establishment of vertical alignment. This

is because the elevation of the existing ground along the centreline is an

important consideration in establishing the vertical alignment. The process of

designing the vertical alignment begins with plotting a profile of the existing

terrain, and a tentative horizontal centreline must already be established in order

to do this.


Chapter 2: Necessity

2.1 Necessity

The need for proper geometric design of a track arises because of the

following considerations :

o To ensure the smooth and safe running of trains

o To achieve maximum speeds

o To carry heavy axle loads

o To avoid accidents and derailments due to a defective permanent

way

o To ensure that the track requires least maintenance.

o For good aesthetics

Chapter 3: GEOMETRIC CROSS SECTION

3.1 Cross Section

The primary consideration in the design of geometric cross sections for

highways, runways, and taxiways is drainage. Details vary depending on the

type of facility and agency.

Railway cross sections are as shown in Fig.1. The distance between the

rails, as shown in the figure, is what is known as standard gage in North

America. Other gauges are sometimes used. In the case of railroad track, the

shape of the cross section is not intended to provide drainage, since the ballast,

which is permeable material, serves this purpose.


Figure No. 1 (a) Basic Details

Figure No. 1(b) Railroad track geometric cross section


Chapter 4: Gradients

4.1 Gradient

Gradients are provided to negotiate the rise or fall in the level of the

railway track. A rising gradient is one in which the track rises in the direction of

the movement of traffic and a down or falling gradient is one in which the track

loses elevation in the direction of the movement of traffic. A gradient is

normally represented by the distance travelled for a rise or fall of one unit.

Sometimes the gradient is indicated as per cent rise or fall. For example, if there

is a rise of 1 m in 400 m, the gradient is 1 in 400 or 0.25%, as shown in

Fig.2.

Figure No.:2 Rising and falling gradient

Gradients are provided to meet the following objectives.

(a) To reach various stations at different elevations

(b) To follow the natural contours of the ground to the extent possible

(c) To reduce the cost of earthwork.

4.2 Types of gradients.

(a) Ruling gradient

(b) Pusher or helper gradient

(c) Momentum gradient

(d) Gradients in station yards


4.2. (a) Ruling Gradient

The ruling gradient is the steepest gradient that exists in a section. It

determines the maximum load that can be hauled by a locomotive on that

section. While deciding the ruling gradient of a section, it is not only the

severity of the gradient but also its length as well as its position with respect to

the gradients on both sides that have to be taken into consideration. The power

of the locomotive to be put into service on the track also plays an important role

in taking this decision, as the locomotive should have adequate power to haul

the entire load over the ruling gradient at the maximum permissible speed.

The extra force P required by a locomotive to pull a train of weight W on

a gradient with an angle of inclination θ is , Rising gradient 1 in 400 (0.25%)

Falling gradient (0.25%) 1 on 400

P = W Sinθ

= W tanθ (approximately, as θ is very small)

= W × gradient

Indian Railways does not specify any fixed ruling gradient owing to

enormous variations in the topography of the country, the traffic plying on

various routes, and the speed and type of locomotive in use on various sections.

Generally, the following ruling gradients are adopted on Indian Railways when

there is only one locomotive pulling the train.

In plain terrain: 1 in 150 to 1 in 250

In hilly terrain: 1 in 100 to 1 in 150

Once a ruling gradient has been specified for a section, all other gradients

provided in that section should be flatter than the ruling gradient after making

due compensation for curvature.


Figure No.:3 Ruling Gradient

4.2. (b) Pusher or Helper Gradient

In hilly areas, the rate of rise of the terrain becomes very important when

trying to reduce the length of the railway line and, therefore, sometimes

gradients steeper than the ruling gradient are provided to reduce the overall cost.

In such situations, one locomotive is not adequate to pull the entire load, and an

extra locomotive is required.

When the gradient of the ensuing section is so steep as to necessitate the

use of an extra engine for pushing the train, it is known as a pusher or helper

gradient. Examples of pusher gradients are the Budni–Barkhera section of

Central Railways and the Darjeeling Himalayan Railway section.

4.2. (c) Momentum gradient

The momentum gradient is steeper than the ruling gradient and can be

overcome by a train because of the momentum it gathers while running on the

section. In valleys, a falling gradient is sometimes followed by a rising gradient.

In such a situation, a train coming down a falling gradient acquires good speed

and momentum, which gives additional kinetic energy to the train and allows it

to negotiate gradients steeper than the ruling gradient. In sections with

momentum gradients there are no obstacles provided in the form of signals, etc.,

which may bring the train to a critical juncture


Figure No.:4 Momentum gradient

4.2. (d) Gradients in station yards

The gradients in station yards are quite flat due to the following reasons.

(a) To prevent standing vehicles from rolling and moving away from the

yard due to the combined effect of gravity and strong winds.

(b) To reduce the additional resistive forces required to start a locomotive

to the extent possible.

It may be mentioned here that generally, yards are not levelled completely and

certain flat gradients are provided in order to ensure good drainage. The

maximum gradient prescribed in station yards on Indian Railways is 1 in 400,

while the recommended gradient is 1 in 1000.


4.2. (e) Grade Compensation on Curves

Curves provide extra resistance to the movement of trains. As a result, gradients

are compensated to the following extent on curves:

(a) On BG tracks, 0.04% per degree of the curve or 70/R, whichever is

minimum.

(b) On MG tracks, 0.03% per degree of curve or 52.5/R, whichever is

minimum.

(c) On NG tracks, 0.02% per degree of curve or 35/R, whichever is

minimum where R is the radius of the curve in metres.

The gradient of a curved portion of the section should be flatter than the ruling

gradient because of the extra resistance offered by the curve.

Example:

Find the steepest gradient on a 2° curve for a BG line with a ruling gradient of 1

in 200.

Solution

(i) Ruling gradient = 1 in 200 = 0.5%

(ii) Compensation for a 2° curve = 0.04 × 2 = 0.08%

(iii) Compensated gradient = 0.5 – 0.08 = 0.42% = 1 in 238

The steepest gradient on the curved track is 1 in 238.


Chapter 5: Curves

5.1 Curves

Curves are introduced on a railway track to bypass obstacles, to provide

longer and easily traversed gradients, and to pass a railway line through

obligatory or desirable locations.

Horizontal curves are provided when a change in the direction of the track

is required and Vertical curves are provided at points where two gradients meet

or where a gradient meets level ground.

Curve is defined either by radius or its degree

5.2 Maximum Degree of a Curve

The maximum permissible degree of a curve on a track depends on

various factors such as gauge, wheel base of the vehicle, maximum permissible

super elevation, and other such allied factors. The maximum degree or the

minimum radius of the curve permitted on Indian Railways for various gauges is

given in Fig 5.

Figure No.:5 Maximum Degree of a Curve

(Source: dl4a.org/uploads/pdf/EbookRailwayEngineering.pdf)


Chapter 6: Superelevation

6.1 Superelevation

The following terms are frequently used in the design of horizontal

curves. Superelevation or cant (Ca) is the difference in height between the outer

and the inner rail on a curve. It is provided by gradually lifting the outer rail

above the level of the inner rail. The inner rail is taken as the reference rail and

is normally maintained at its original level. The inner rail is also known as the

gradient rail.

6.2 Objective Of Providing Superelevation

The main functions of superelevation are the following :

(a) To ensure a better distribution of load on both rails

(b) To reduce the wear and tear of the rails and rolling stock

(c) To neutralize the effect of lateral forces

(d) To provide comfort to passengers

6.3 Centrifugal Force on a Curved Track

A vehicle has a tendency to travel in a straight direction, which is

tangential to the curve, even when it moves on a circular curve. As a result, the

vehicle is subjected to a constant radial acceleration:

Radial acceleration = g = V2 /R

Where, V = velocity (metres per second) and

R = Radius of curve (metres).

This radial acceleration produces a centrifugal force which acts in a radial

direction away from the centre.


The value of the centrifugal force is given by the formula

Force = mass × acceleration

F = m × (V2 /R)

= (W/g) × (V2 /R)

Where, F = Centrifugal force (tonnes),

W = Weight of the vehicle (tonnes),

V = Speed (metre/sec),

g = Acceleration due to gravity (metre/sec2 ), and

R = Radius of the curve (metres).

To counteract the effect of the centrifugal force, the outer rail of the curve

is elevated with respect to the inner rail by an amount equal to the

superelevation. A state of equilibrium is reached when both the wheels exert

equal pressure on the rails and the superelevation is enough to bring the

resultant of the centrifugal force and the force exerted by the weight of the

vehicle at right angles to the plane of the top surface of the rails. In this state of

equilibrium, the difference in the heights of the outer and inner rails of the curve

known as equilibrium superelevation.

Figure No.:6 Centrifugal Force


6.4 Formula for Superelevation

The θ is the angle that the inclined plane makes with the horizontal line, then

where ,

e = Superelevation,

G= Gauge,

V = Velocity,

g = Acceleration due to gravity, and

R = Radius of the curve.

6.5 Thumb Rules for Calculating Superelevation in the Field

A field engineer can adopt the following thumb rules for determining the

superelevation of any curve


Super elevation for BG in cm

For MG tracks

Super elevation = three-fifths of the above formula

The equilibrium speed is used in this formula

6.6 Types of Cant

The cant are further divided on the bases of speed:

Equilibrium cant

Cant deficiency ( Cd )

Cant excess ( Ce )

6.6.1 Equilibrium cant

Value of super elevation derived from the equation using equilibrium speed

6.6.2 Cant deficiency ( Cd )

Cant deficiency (Cd) occurs when a train travels around a curve at a speed

higher than the equilibrium speed. It is the difference between the theoretical

cant required for such high speeds and the actual cant provided. Maximum

permissible Cd : 7.6cm (BG), 5.1cm (MG), 3.8cm (NG).

6.6.3 Cant excess ( Ce )

Cant excess (Ce) occurs when a train travels around a curve at a speed lower

than the equilibrium speed. It is the difference between the actual cant provided

and the theoretical cant required for such a low speed.


Chapter 7: Widening of Gauge on Curve

7.1 Widening of Gauge on Curve

When vehicle moves onto a curve, the flange of the outside wheel of the

leading axle continues to travel in a straight line till it rubs against the rail. Due

to the coning of wheels ,the outside wheel travels a longer distance compared to

the inner wheel. In an effort to make up for the difference in the distance

travelled by the outer wheel and the inner wheel, the inside wheels slip

backward and the outer wheels skid forward.

The widening of the gauge on a curve has, in fact, tends to decrease the wear

and tear on both the wheel and the track

The widening of the gauge on curves can be calculated using the formula

Extra width on curves

w = 13(B+L)2/R

Where,

B is the wheel base of the vehicle in metres,

R is the radius of the curve in metres,

L =0.02(h2 + Dh)

1/2 is the lap of the flange in metres,

h is the depth of flange below top of the rail(cm),

D is the diameter of the wheel of the vehicle (cm).


Figure No.:7 Widening of Gauge on Curve

(Source:www.indianrailways.gov.in/railwayboard/uploads/codesmanual/IRPWM/Permanent

WayManual)


Chapter 8: References

http://dl4a.org/uploads/pdf/EbookRailwayEngineering

http://trainguard.in/horizontalcurve&submit&posttypeproduct

http://www.indianrailways.gov.in/railwayboard/uploads/codesmanual/IR

PWM/PermanentWayManual

http://teacher.buet.ac.bd/cfc/curve

http://trainguard.in/?s=horizontal+curve&submit.x=0&submit.y=0&post_type=product