The GATE Grind

GATE 2019 CE (CE1) – Question 27

Geotechnical Engineering · Effective stress principle and quicksand condition · 1 mark · Multiple choice

Total stress, effective stress, hydraulic gradient and critical gradient in soil are σ, $\sigma^\prime$, i and $i_c$. At initiation of quicksand, which is true?

  1. $\sigma^\prime\ne0,\ i=i_c$
  2. $\sigma^\prime=0,\ i=i_c$
  3. $\sigma^\prime\ne0,\ i\ne i_c$
  4. $\sigma=0,\ i\ne i_c$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) $\sigma^\prime=0,\ i=i_c$

Explanation

At the critical upward gradient, seepage force balances submerged soil weight. Effective grain-contact stress becomes zero while total stress need not vanish. Therefore $\sigma^\prime=0$ and $i=i_c$: **B**.