Question

During CBR test, the load sustained by a re-moulded soil specimen at \(5\,\mathrm{mm}\) penetration is \(50\,\mathrm{kg}\). The CBR value of the soil will be

• A. \(10\%\)
• B. \(5\%\)
• C. \(3.6\%\)
• D. \(2.4\%\)

Hint:

Standard CBR loads: \[ \boxed{ \begin{aligned} 2.5~\mathrm{mm} &: 1370~\mathrm{kg}\\ 5~\mathrm{mm} &: 2055~\mathrm{kg} \end{aligned} } \]

Answer 1

The Correct Option is D

Step 1: Recalling the reference load.
The California Bearing Ratio test compares the load a soil specimen sustains against the load a standard, well graded crushed stone sample sustains at the same penetration. At $5\,\text{mm}$ penetration, this standard load is fixed at $2055\,\text{kg}$.
Step 2: Setting up the ratio.
$\text{CBR} = \dfrac{\text{Load on test specimen}}{\text{Load on standard specimen}} \times 100$. Here the test specimen sustains $50\,\text{kg}$ at that same $5\,\text{mm}$ penetration.
Step 3: Working out the percentage.
Dividing gives $\dfrac{50}{2055} = 0.02433$, and multiplying by $100$ gives about $2.43\%$, which rounds to $2.4\%$.
\[ \boxed{2.4\%} \]