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

Explanation:

1. Definition of Rail Wear
   Rail wear refers to the gradual loss of material from the rail surface due to friction, impact, and stress from repeated wheel contact. It affects the rail’s profile, strength, and alignment over time.

2. Maximum Wear in Sharp Curves
   On sharp curves, the outer rail experiences more lateral force due to centrifugal action, and the flange of the wheel exerts greater pressure, causing gauge face wear. This is the most severe location for rail wear.

3. Types of Rail Wear

   • Top wear: due to vertical loading from train wheels.

   • Side (gauge face) wear: from lateral thrust in curves.

   • End wear: due to improper jointing or impact at rail ends.

   • Corrugation: formation of waves or undulations due to vibration.

4. Factors Influencing Rail Wear

   • Traffic volume and speed

   • Track geometry (curves vs. tangents)

   • Rail material and hardness

   • Axle loads and wheel profiles

   • Lubrication and maintenance practices

 Additional InformationOther Types of Rail Damage 

• Crushing of Rail Head:  Happens under high axle loads, especially if material is soft or under-lubricated. It leads to deformation of the rail crown, which affects riding comfort and increases the risk of derailment.

• Rail Fractures and Cracks: Initiated by internal flaws or fatigue, aggravated by repeated impact loading. Cracks often originate from bolt holes, fishplate areas, or welded joints.

• Shelling and Spalling: Shelling occurs when small pieces of metal flake off due to internal fatigue. Spalling is surface chipping due to impact or stress concentrations, often seen near switches or crossings.

• Rail Buckling: Common in extreme heat, when thermal expansion causes longitudinal stress. If rails are not adequately anchored, it results in track misalignment and severe safety hazards.

• Plastic Flow: Repeated stress can cause metal flow on the rail surface, especially in soft rails. This leads to change in rail profile, requiring grinding or replacement.

• Squats and Corrugations: Squats are small surface defects from rolling contact fatigue. Corrugations are wave-like wear patterns caused by vibration, leading to noise and uneven running surfaces.

Explanation:

• Switch angle is the angle between the stock rail and the tongue (switch) rail at the point where the tongue rail starts diverging.

• It determines the divergence rate of the moving rail from the fixed stock rail in a turnout or switch.

• A smaller switch angle allows smoother transitions and is suitable for higher speeds, while a larger angle is used where space is limited.

• The switch angle plays a key role in determining the length of the turnout, comfort, and safety of train movement through diverging routes.

• It directly influences how quickly the rail diverges, thus affecting the lateral force exerted on the wheels and track.

Additional InformationHeel Divergence

• Heel divergence is the horizontal distance between the tongue rail and the stock rail at the heel end, which is the rear end of the tongue rail.

• It represents the total lateral shift the tongue rail achieves from its starting (closed) position.

Flange-way Clearance

• Flange-way clearance is the gap provided between the rail and the check rail or wing rail to allow free movement of the wheel flange.

• It ensures that the wheel flange doesn't strike the check rail or crossing nose during passage.

• It is a critical factor in the design of crossings and check rails, but not related to the switch angle.

Explanation:

The relation between the radius (R, in feet) and the degree of curve (D, in degrees) for a simple circular curve is given by the formula:

• This is commonly used in railway and highway alignment design when the degree of curve is defined based on a chord length of 100 feet.
• The formula provides an easy way to convert between the degree of curve and the corresponding radius of curvature.

 Additional Information

Degree of Curve (D):

• The degree of curve is defined as the central angle subtended by a chord of fixed length, typically 100 feet in standard practice.

• It represents the sharpness of a curve — a larger degree of curve indicates a sharper curve, while a smaller degree indicates a flatter curve.

• It is used widely in geometric design of roads and railways for laying out curves in the field and in design drawings.

• The degree of curve provides a convenient way to express curvature without needing to specify the radius directly.

 Radius of Curve (R):

• The radius is the distance from the center of the circle to any point on the curve. It directly determines the curvature — a smaller radius means a sharper curve.

• Knowing the radius helps in calculating transition curves, vehicle dynamics, and super-elevation requirements for safe turning.

• In practice, curves with larger radii are preferred for higher-speed routes to reduce centrifugal force and increase comfort.

Explanation:

• Crossing number (also called frog number) in railway engineering is the ratio of divergence between two tracks at the crossing.

• It is expressed as 1 in N, meaning for every N units along the main line, the diverging line moves 1 unit away.

• To ensure smooth and safe travel at higher speeds, flatter crossings (lower divergence angles) are required.

• Indian Railways typically uses a 1 in 16 crossing for main line high-speed routes.

• A sharper angle crossing (lower N, like 1 in 8½) would cause discomfort or derailment at high speeds — hence avoided for main lines.

 Additional Information

• 1 in 8½ — Used in yards, loop lines, where speeds are low.

• 1 in 12 — Used for medium speed turnouts.

• 1 in 16 — Standard for high-speed routes.

• 1 in 20 — Used in very high-speed or dedicated passenger corridors.

Explanation:

• The ruling gradient is the steepest gradient permitted for a section of railway under normal operating conditions.
• On plain terrain in Indian Railways, the standard ruling gradient ranges from 1 in 150 to 1 in 200

• Since it's the maximum allowed, 1 in 150 represents the steepest permissible gradient in plains. 

 Additional Information

Hilly Terrain Ruling Gradient:

• Ranges between 1 in 100 and 1 in 150, reflecting the need to manage steeper slopes.

Momentum Gradient:

• Can be steeper than the ruling gradient because it relies on the train's momentum to climb short rises 

Pusher (Helper) Gradient:

• Requires additional locomotives to assist trains on very steep slopes; common in mountain sections such as the Western Ghats at 1 in 37 .

Station Yard Gradient:

• Kept very low (flat) for safety and drainage—up to 1 in 400 —to prevent runaway stationary trains .

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 

∴ 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.

4. Size of ballast for wooden sleepers is 50 mm and for metal sleepers is 40 mm.

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:

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

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

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

= 59.52 mm

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.