A coarse-grained soil has a void ratio of 0.75 and specific gravity of 2.75. The critical gradient at which quick sand condition occurs is
- A0.75
- B0.50
- C1.00Correct
- D0.25
Solution
Concept
Critical hydraulic gradient
Formula
ic = (G − 1) / (1 + e)
Step-by-step solution
1. ic = (2.75 − 1) / (1 + 0.75) = 1.75 / 1.75 = 1.0.
Explanation
Quicksand occurs when the upward hydraulic gradient equals the critical gradient, so effective stress becomes zero. For most sands the critical gradient is approximately 1.
Shortcut
ic = (G − 1)/(1 + e) ≈ 1.
Common mistake
Forgetting to subtract 1 from G.
Correct answer: C) 1.00