Question

Using IRC : 37-1984 "Guidelines for the Design of Flexible Pavements" and the following data, choose the total thickness of the pavement.
$\begin{array}{cc}\text{Number of commercial vehicles}& 2723veh/day\\ \text{when construction is completed}& \\ \text{Annual growth rate of the traffic}& 5\%\\ \text{Design life of the pavement}& 10yr\\ \text{Vehicle damage factor}& 2.4\\ \text{CBR value of the subgrade soil}& 5\%\end{array}$

Data for 5% CBR value
$\begin{array}{cc}\text{Number of standard axles(msa)}& \text{Total thickness(mm)}\\ 20& 620\\ 25& 640\\ 30& 670\\ 40& 700\end{array}$

• A. 640 mm
• B. 670 mm
• C. 620 mm
• D. 700 mm

Answer 1

The correct option is B 670 mm

Number of commercial vehicles per day when construction is completed,
A = 2723

Annual growth rate,
r = 5%

Design life,
n = 10 year

Vehicle damage factor,
F = 2.4

Number of standard axles,
$N_s=\frac{365A\left[\right(1+r{)}^n-1]}{r}\times F$
$=\frac{365\times 2723\left[\right(1.05{)}^{10}-1]\times 2.4}{0.05}$
$=30\times {10}^6$
standard axle = 30 msa
From table for 30 msa,
Thickness of pavement = 670 mm