Question

If g1 = + 1.2% and g2 = + 0.8% and rate of change of grade = 0.1% per 20 m chain, then the length of the vertical curve is
1. 10 m
2. 15 m
3. 30 m
4. 80 m

Answer 1

Correct Answer - Option 4 : 80 m

Concept:

Total Grade = Grade 1 – Grade 2

Length of curve = (Total grade/Rate of change of grade per chain length) × Length of chain

Calculation:

An upgrade of + 1.2% joins another upgrade of + 0.8%.

Grade = + 1.2 – (+ 0.8) = 0.4 % (Upward)

Change of grade is 0.1% per 20 m chain.

L = (0.4/0.1) × 20 = 80 m