Question

A partially-saturated soil sample has natural moisture content of 25% and bulk unit weight of 18.5 kN/m³. The specific gravity of soil solids is 2.65 and unit weight of water is 9.81 kN/m³. The unit weight of the soil sample on full saturation is

• A. 21.12 kN/m³
• B. 19.03 kN/m³
• C. 20.12 kN/m³
• D. 18.50 kN/m³

Hint:

To find the unit weight of the soil on full saturation, add the contribution from the moisture content to the given bulk unit weight.

Answer 1

The Correct Option is B

The unit weight of the soil on full saturation can be calculated using the formula: \[ \gamma_{sat} = \gamma_{bulk} + \frac{w}{G} \cdot \gamma_{w} \] Where:
- \( \gamma_{sat} \) is the unit weight of the soil when fully saturated,
- \( \gamma_{bulk} \) is the given bulk unit weight of the soil (18.5 kN/m³),
- \( w \) is the moisture content (25% or 0.25),
- \( G \) is the specific gravity of the soil solids (2.65),
- \( \gamma_w \) is the unit weight of water (9.81 kN/m³).
Substitute the values into the equation: \[ \gamma_{sat} = 18.5 + \frac{0.25}{2.65} \times 9.81 = 18.5 + 0.923 \approx 19.03 \, \text{kN/m³}. \] Final Answer: 19.03 kN/m³