The effective stress on the surface of sea bed is?
- Aalways 0Correct
- Bincreases with depth of sea bed from sea level
- Calways > 0
- Dnone of these
Solution
Concept
Effective stress at the sea bed surface
Formula
σ′ = σ − u
Step-by-step solution
1. At the sea bed surface, total stress σ = γw h (weight of water above). 2. Pore water pressure u = γw h. 3. σ′ = σ − u = 0.
Explanation
At the surface of the sea bed there is no soil above, so the whole stress is carried by water and the effective stress is zero. Below the surface the effective stress increases with the submerged weight of soil.
Shortcut
Surface of the ground (dry or submerged) → effective stress = 0.
Common mistake
Including the water depth above the bed as effective stress.
Correct answer: A) always 0