Which of the following is the value of limiting gradient for a road to be constructed in a steep terrain?
- A1 in 20
- B1 in 16.7
- C1 in 14.3Correct
- D1 in 12.5
Solution
Concept
Limiting Gradient in Steep Terrain
Formula
No formula; it is a standard empirical value recommended by IRC guidelines (Limiting Gradient = Vertical Rise / Horizontal Distance).
Step-by-step solution
Recall that as per IRC guidelines, the limiting gradient for roads in steep terrain is 1 in 14.3 (7%). Thus, option C is correct.
Explanation
As per the Indian Roads Congress (IRC) guidelines, 1 in 14.3 (or 7%) is the recommended limiting gradient for roads in steep terrain. A limiting gradient is a steeper slope permitted for short stretches when the topography makes the standard ruling gradient impractical or excessively expensive to implement.
Shortcut
Remember the IRC gradient percentages for steep/mountainous terrain in increasing order of steepness: - Ruling Gradient = 6% (1 in 16.7) - Limiting Gradient = 7% (1 in 14.3) - Exceptional Gradient = 8% (1 in 12.5)Mnemonic: "R-L-E" = "6-7-8%". Since 7% corresponds to 100 / 7 = 14.3, Limiting Gradient is 1 in 14.3.
Common mistake
Students often confuse the limiting gradient (1 in 14.3 or 7%) with either the ruling gradient (1 in 16.7 or 6%) or the exceptional gradient (1 in 12.5 or 8%) for steep terrain.
Correct answer: C) 1 in 14.3