Test: Gradients & Grade Compensation - Civil Engineering (CE) MCQ

Gradients are provided so that the rise or fall in the track’s path can be easily traversed. A down gradient also called as falling gradient is the one in which drop of elevation in the direction of movement is recorded.

IRC Recommendations for grade compensation:
IRC gave the following guidelines for grade compensations:-

• Grade compensation is not required for grades flatter than 4% because the loss of tractive force is negligible.
• Grade compensation is  where R – radius of horizontal curve in m.
• The maximum grade compensation is limited to 75/R %

Calculation:
Given:
The gradient of the Curve = (1/25) x 100 = 4%

⇒ GC = 0.75%
∴ CompensatedGradient = ((1/25) ×100)−0.75 = 4−0.75 = 3.25%
But, Compensated Gradient (C.G) should be ≥ 4 %
Since the gradient of the curve is 4 %, no grade compensation is required. 
∴ C.G = 4%

Gradient is represented as the distance travelled for a rise or fall of 1 unit distance. 1 in 400 means a rise of 1m is recorded after travelling 400m. 1 in 400 is also represented as 0.25%.

The ruling gradient adopted by the Indian railways in hilly terrain can be from 1 in 100 to 1 in 150. For plain terrain it can be from 1 in 150 to 1 in 250.

Momentum gradient is steeper than the Ruling gradient. When a train travels on a falling gradient it gains momentum and can travels on the rising gradient which might be steeper than the Ruling gradient.

On curves the locomotive experiences extra resistance to its movement. Thus gradients on a curve should be flatter because more resistance can cause uncomfortable journey.

Ruling gradient = 1 in 200 = 0.5%
Compensation = 0.04 x 3 = 0.12%
Compensated gradient = 0.5-0.12 = 0.38%
= 1 in 263.

Ruling gradient is the steepest gradient that is present in the entire section. It determines the maximum load that can be carried by the section. The power of locomotive should also be considered while deciding this gradient.

Pusher gradients can sometimes be steeper than Ruling gradient. If one locomotive is not sufficient to pull the entire load, another locomotive or engine can be used. It is also known as Helper gradient.

Gradient compensation for BG is 0.04% per degree of curve or 70/R whichever is minimum. For MG it is 0.03% per degree of curve or 52.5/R whichever is minimum.