Direction: A sand layer found at sea floor under 20 m water depth is characterised with relative density = 40%, maximum void ratio = 1.0, minimum void ratio = 0.5, and specific gravity of soil solids = 2.67. Assume the specific gravity of sea water to be 1.03 and the unit weight of fresh water to be 9.81 kN/m3
-
What would be the effective stress (rounded off to the nearest integer value of kPa) at 30 m depth into the sand layer?
-
- 77 kPa
- 273 kPa
- 268 kPa
- 281 kPa
Correct Option: D
Relate density, ID = .40 (40%)
emax = 1, emin = 0.5
| ID = | emax - emin |
| 4 = | 1 - 5 |
∴ e = 0.8
Effective stress = γsub.h
| γsub = | .γ'w | (1 + e) |
γ'w = unit weight of sea water.
∴ γ'w = G × γw = 1.03 × 9.81 = 10.1 kw/m3.
| ∴ γsub = | (1 + e) |
| = | × 10.1 = 9.37 mN/m3. | (1 + .8) |
Effective stress = 9.37 × 30 = 281.1 kN/m2 = 281. 1 kPa
