Question

A subgrade soil sample was tested using standard CBR apparatus and the observations are given below

$\begin{array}{cc}\text{Load (kg)}& \text{Penetration (mm)}\\ 60.5& 2.5\\ 80.5& 5.0\end{array}$

Assuming that the load-penetration curve is convex throughout, the CBR value(%) of the sample is

• A. 5.5
• B. 4.4
• C. 6.5
• D. 3.9

Answer 1

The correct option is B 4.4

CBR value at 2.5 mm penetration

= $\frac{\text{Load}}{\text{Standard load}}\times 100$

= $\frac{60.5}{1370}\times 100=4.416\%$

CBR value at 5 mm penetration

$=\frac{80.5}{2055}\times 100=3.917\%$

CBR value at 2.5 mm penetration should be higher than that of 5 mm

Hence, CBR value of sample = 4.4%