Track Design MCQ Quiz - Objective Question with Answer for Track Design - Download Free PDF

The choice of different gauges of railway track depends upon following important factors and prevailing conditions in the region.

Traffic condition: If the intensity of traffic on the track is likely to be more, a gauge wider than the standard gauge is suitable.

Development of areas: To connect a remote location of a smaller population to the world, a narrow gauge may be suitable.

Cost of the track: It is directly proportional to the width of the gauge of railway track. As gauge width increases, the cost of ballast, sleepers, rails, etc increase proportionally.

Speed of Movement: The speed of the train is a function of the diameter of the wheel of a train, the diameter of a wheel is usually about 0.75 times the gauge width. Therefore, as the gauge width increases, wheel diameter increases and thus the speed of the train increases.

Explanation:

Standard Gauge for BG: In India, the Broad Gauge (BG) is defined as having a track gauge of 1676 mm (5 feet 6 inches). This is the most commonly used gauge in the country and accounts for the majority of the railway network.

• Significance of 1676 mm Gauge:

  • The 1676 mm Broad Gauge is used for long-distance passenger trains, freight trains, and high-speed services across India.

  • It provides better stability and allows for the operation of faster trains compared to narrower gauges (like meter gauge or narrow gauge).

  • The BG tracks can handle larger and heavier trains, which is essential for transporting both passengers and freight over long distances efficiently.

  • Over 80% of the total track length in India is Broad Gauge.

Additional Information Other Gauges in India:

• Standard Gauge (1435 mm): This is mostly used in some specialized or high-speed rail corridors, like the Mumbai-Ahmedabad bullet train project.

• Meter Gauge (1000 mm) and Narrow Gauge (762 mm or less): These are used for shorter, regional, or mountainous routes, though their use is gradually being replaced by Broad Gauge for better efficiency.

Concepts:

The hauling capacity of a railway locomotive is given as:

H = μ × W × N

H = Hauling power

N = number of pairs of driving wheels

W = weight exerted on the driving wheels

μ = coefficient of friction 

Calculation:

Given: μ = 0.3, W = 23 tonnes

For Locomotive 1-4-1:

Nos of driving wheels = 4

Nos. of pair of driving wheels are, N = 4/2 = 2

Now, the hauling capacity is given as:

H = 0.3 × 23 × 2 = 13.8 tonnes.

Concept:

Development length:

(i) The calculated tension or compression in any bar at any section shall be developed on each side of the section by an appropriate development length or end anchorage or a combination thereof.

(ii) Development length can be calculated as:
\({L_d} = \frac{{ϕ × 0.87{f_y}}}{{4{τ _{bd}}}}\)

Where, ϕ = Diameter of bar

τbd = Design bond stress = Permissible value of average bond stress

The value of bond stress is increased by 60% for a deformed bar in tension and a further increase of 25% is made for bars in compression.

Calculation:

Given,

ϕ = 20 mm, τbd = 1.4 N/mm2 (In tension), fy = 415 MPa

∵ Bar in compression, so Increased the value of τbd by 25% and for deformed bar it is increased by 60 %

So, τbd = 1.4 × 1.25 × 1.6 = 2.8 N/mm2

Development length, \({L_d} = \frac{{ϕ × 0.87{f_y}}}{{4{τ _{bd}}}}\) 

\({L_d} = \frac{{20 × 0.87 × 415}}{{4 × 2.8}}\) = 645 mm

Concept:

Relationship between sleeper spacing, width of sleeper, and depth of ballast cushion is given by the following formula:

Sleeper Spacing = Width of Sleeper + (2 × Depth of Ballast Cushion)

Calculation:

Given Data:

Let D = depth of ballast cushion

Sleeper Spacing = 68.4 cm

Width of sleeper = 25.4 cm

Putting these data in above equation, we get,

68.4= 25.4 + (2 × D)

So,

Depth of Ballast Cushion, \(D = \frac{{68.4 - 25.4}}{2} = 21.5\;cm\)

Explanation:

Ballast

It is the granular material that is placed and packed below and surrounding the sleeper.

Functions:

1. It transmits the load from sleepers to subgrade

2. Provide good drainage.

The characteristics of ballast are:

1. The depth of ballast for different type tracks is:

For BG: 20-25 cm

For MG: 15-20 cm

For NG: 15 cm

2. The quantity of stone ballast required for one-meter length of track for different type of tracks is as follow:

For BG – 1.036 m³.

For MG – 0.71 m³.

For NG – 0.53 m³.

3. The size of ballast depends on the type of sleeper and location of track and its is given as:

For Wooden sleeper - 5 cm

For Metal sleeper - 4 cm

For turnouts and cross-over - 2.5 cm

CONCEPT

Length of 1 rail(N) is taken as 13m

Number of sleepers = N + 3

Spacing of sleepers(S) = (length of 1 rail * 100) / number of sleepers (cm) 

Optimum depth of blast cushion = (S - W ) / 2

Given

Sleeper density = N+ 3 

width of the sleeper is 20.25 cm

CALCULATION

Number of sleepers = 13 + 3 = 16

Spacing of sleepers(S) = 13 X 100 / 16 = 81.25cm

Width of sleepers(W) = 20.25 cm

Minimum depth of blast cushion = (S - W ) / 2 

= (81.25 - 20.25) / 2 

= 30.5 cm (ans)

Concept

Grade compensation (GC) for BG = 0.04% per degree of curve

Calculation

Given,

Degree of curve D = 3° 

Ruling Gradient = 1 in 250 

So for 3° curve, compensation,

= 0.04 × 3 = 0.12%

∴ Ruling gradient \(= \frac{1}{{250}} \times 100 = 0.4{\rm{\% }}\)

∴ The actual ruling gradient considering the grade compensation of curvature = 0.4 - 0.12 = 0.28%

Concept:

The points and crossing are the vital components of track asset; necessary for diversion of traffic from one track to another track, such diversion may be necessitated for giving precedence to faster trains in the same direction, giving passage to a train moving in the opposite direction or for connecting places not on the direct line of the track.

Constituents of the points and crossing are explained below:

1. Turnout - The term denotes points and crossing with the lead rails.

2. Tongue rail - It is a tapered moveable rail, connected at its thickest end to the running rail.

3. Stock rail - It is the running rail, against which a tongue rail functions.

4. Switch - A pair of tongues with stock rail with necessary connections and fittings.

5. Points - A pair of tongue rail with their stock rails are termed as points.

6. Crossing - A crossing is a device introduced at the junction where two rails cross to permit the wheel flange of railway vehicle to pass from one track to another track.

7. Heel of the switch - It is an imaginary point on the gauge line midway between the end of the lead rail and the tongue rail in case of loose heel switches In case of fixed heel switches, it is a point on the gauge line of tongue rail opposite the centre of heel block.

8. Lead - The track portion between heels of the switch to the beginning of crossing assembly is called the lead.

9. Turn – in – curve - The track portion between the heel of crossing to the fouling marks is called the turn – in – curve.

For points & crossing, the maximum of nominal size of the ballast is 25 mm.

Other Points:

1. Points & crossing provide flexibility of movement by connecting one lien to another according to requirements.

2. They also help for imposing restrictions on turnouts which further retards the speed of the train.

3. The main function of ballast is to hold the sleepers and convert line load to uniformly distributed load.

Explanation

Throw of switch: 

(i) It is the distance between the running face of the stock rail and the toe of the tongue rail.

(ii) Its limiting values are 95-115 mm for BG routes and 89-100 mm for MG routes.

Additional Information

Some other important terms are as follows:

Switch angle: It is the angle between the gauge faces of the stock rail and the tongue angle.

Heel clearance: It is the distance between the running edge of the stock rail and the switch rail at the switch heel.

Its recommended value on BG is 133 mm, 121 mm to 117 mm for MG and 98 mm for NG track respectively.

Check rails: These are the rails provided to guide the wheel flanges, while the opposite wheel is jumping the gap.

Flange way clearance: It is the distance between the adjacent faces of the stock rail and the check rail. Its minimum value is 60 mm.

Concept:

Superelevation:

To counteract the effect of centrifugal force, the level of the outer rail is raised above the inner rail by a certain amount to introduce the centripetal force.

This raised elevation of the outer rail above the inner rail at a horizontal curve is called superelevation.

For any gauge super elevation ‘e’ (in m) is given as

\(e = \frac{{{\rm{GV}}^2}}{{127{\rm{R}}}}\)

Where, G = Gauge distance

V = velocity in Kmph

R = Radius of curve

Calculation:

Given,

G = Gauge distance = 1.68 m

V = velocity in Kmph = 60

R = Radius of curve = 800 m

\(e = \frac{{{\rm{GV}}^2}}{{127{\rm{R}}}}\)

Concept:

Grade compensation:

The ruling gradient is the maximum gradient on a particular section, but if a curve lies on a ruling gradient, the resistance due to gradient is increased by that due to curvature, and this further increases the resistance beyond the ruling gradient. In order to avoid resistances beyond the allowable limits, the gradients are reduced on curves, and this reduction is known as the grade compensation for the curve.

Allowable ruling gradient = Ruling gradient - Grade compensation 

Grade compensation (GC) for BG = 0.04% per degree of curve
Grade compensation (GC) for MG = 0.03% per degree of curve
Grade compensation (GC) for NG = 0.02% per degree of curve

Calculation

Given,

Degree of curve D = 5° 

Ruling Gradient = 1 in 200 

So for 5° curve, compensation,

= 0.04 × 5 = 0.2%

∴ Ruling gradient = (1/200) × 100 = 0.5%

∴ Allowable gradient = (0.5 - 0.2)% = 0.3/100 = 1/333.33

∴ Allowable Gradient = 1 in 334

Explanation:

(i) Total number of the sleeper at point and crossing depend upon the turnout and in indian railway generally, two types of turnout are provided i.e. 1 in 12 and 1 in 8.5

(ii) For 1 in 12 turnouts, the total number of sleeper = 70

(iii) For 1 in 8.5 turnouts, the total number of sleeper = 62

Explanation:

The following materials for Ballast can be used on the railway track.

1. Broken Stone

2. Gravel

3. Cinders / Ashes

4. Sand

5. Kankars

6. Moorum

7. Brick Ballast

Among above materials, broken stone from Igneous rocks like quartzite and granite forms the excellent ballast materials. When these are not available then lime stone and sand stone can also be used as good ballast material.

Some of the main functions of ballast are followings:

a) To provide firm and level bedded foundation for the sleepers and rails to rest on

b) To protect the surface of subgrade and to form an elastic bed

c) To transmit and distribute the loads from the sleepers to the subgrade

d) To allow for maintaining correct track level without disturbing the rail road bed

e) To hold the sleepers in position during the passage of trains

f) To provide lateral stability to the track as a whole.