Section 4: Soil and Water Conservation Engineering
Soil Mechanics
Subtopic: Fundamental definitions and relationships
Question Statement:
A saturated soil mass below the groundwater table has a saturated unit weight $\gamma_{sat} = 20.0\text{ kN/m}^3$. Taking the unit weight of water $\gamma_w = 9.81\text{ kN/m}^3$, the submerged buoyant unit weight $\gamma'$ of the soil in $\text{kN/m}^3$ is ________ (round off to 2 decimal places).
Answer Key:
10.19
Step-by-Step Solution & Explanation
The submerged (buoyant) unit weight of soil solids is given by Archimedes' principle:
$\gamma' = \gamma_{sat} - \gamma_w$
Given:
• $\gamma_{sat} = 20.0\text{ kN/m}^3$
• $\gamma_w = 9.81\text{ kN/m}^3$
$\gamma' = 20.0 - 9.81 = 10.19\text{ kN/m}^3$