Question Bank • QB_SWCE_EXP_080 NAT • 2 Marks

Section 4: Soil and Water Conservation Engineering

Soil Mechanics

Subtopic: Mohr's circle of stress

Question Statement:

At a depth of $4.0\text{ m}$ below the ground surface, a saturated soil has a saturated unit weight of $\gamma_{\text{sat}} = 19.81\text{ kN/m}^3$. The water table is at the ground surface. Calculate the effective vertical stress $\sigma'$ at this depth in $\text{kPa}$. (Unit weight of water $\gamma_w = 9.81\text{ kN/m}^3$)

Answer Key:

40

Step-by-Step Solution & Explanation

Submerged unit weight of soil: $\gamma' = \gamma_{\text{sat}} - \gamma_w = 19.81 - 9.81 = 10.0\text{ kN/m}^3$ Effective stress: $\sigma' = \gamma' \times z = 10.0\text{ kN/m}^3 \times 4.0\text{ m} = 40.0\text{ kPa}$
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