Question

The total, neutral and effective vertical stresses (in t/m²) at a depth of 5 m below the surface of a fully saturated soil deposit with a saturated density of 2 t/m³ would respectively be
1. 5, 5 and 10
2. 5, 10 and 5
3. 10, 5 and 10
4. 10, 5 and 5

Answer 1

Correct Answer - Option 4 : 10, 5 and 5

Concept:

Total stress (σ) is made up of two parts

(i) One part is due to pore water pressure (u)

(ii) The other part is due to pressure exerted by the soil skeleton which is called effective stress (σ̅ )

i.e. σ = u + σ̅ 

∴ σ̅ = σ - u

Calculation:

Given, h = 5 m, saturated soil with saturated density (γ_sat) = 2 t/m³

Total stress (σ) = γ_sat × h = 2 × 5 = 10 t/m³

Pore water pressure (u) = γ_w × h = 1 × 5 = 5 t/m³

effective stress (σ̅ ) = σ - u = 10 - 5 = 5 t/m³