Section 4: Soil and Water Conservation Engineering
Soil Mechanics
Subtopic: Fundamental definitions and relationships
Question Statement:
A soil sample has a void ratio $e = 0.60$ and specific gravity of soil solids $G_s = 2.65$. The dry unit weight of the soil in $\text{kN/m}^3$ (taking unit weight of water $\gamma_w = 9.81\text{ kN/m}^3$) is ________ (round off to 2 decimal places).
Answer Key:
16.25
Step-by-Step Solution & Explanation
The relationship for dry unit weight $\gamma_d$ is:
$\gamma_d = \frac{G_s \gamma_w}{1 + e}$
Given:
$G_s = 2.65$
$e = 0.60$
$\gamma_w = 9.81\text{ kN/m}^3$
$\gamma_d = \frac{2.65 \times 9.81}{1 + 0.60} = \frac{25.9965}{1.60} = 16.248\text{ kN/m}^3 \approx 16.25\text{ kN/m}^3$