In a district where the rainfall is heavy, a major district road of WBM pavement, 3·8 m wide, is to be constructed. The height of the crown with respect to the edges is
- A0·058 mCorrect
- B0·072 m
- C0·064 m
- D0·049 m
Solution
Concept
Camber of roads
Formula
Crown height = (width / 2) × camber
Step-by-step solution
1. IRC camber for WBM/gravel roads in heavy rain: 1 in 33 (3%). 2. Crown height = (3.8/2) / 33 = 1.9 / 33 = 0.0576 m ≈ 0.058 m.
Explanation
The camber helps to drain rainwater from the surface; unsurfaced and WBM roads need a steeper camber than bituminous ones.
Why the other options are wrong
0.072, 0.064 and 0.049 m correspond to cambers of 1 in 26, 1 in 30 and 1 in 39.
Shortcut
WBM heavy rain: 1 in 33.
Common mistake
Using the camber for bituminous surfaces (1 in 40).
Correct answer: A) 0·058 m