Question

A coarse-gained soil has a void ratio of 0.78 and specific gravity as 2.67. The critical gradient at which a quick sand condition occurs will be

1. 0.62
2. 0.74
3. 0.82
4. 0.94

Answer 1

Correct Answer - Option 4 : 0.94

Concept:

Critical hydraulic gradient (icr): The quick condition occurs at a critical upward hydraulic gradient ic, when the seepage force just balances the buoyant weight of an element of soil. The critical hydraulic gradient is typically around 1.0 for many soils.

\({i_{cr}} = \frac{{{G_s} - 1}}{{1 + e}} \)

At the critical conditions, the effective stress is equal to zero.

Calculation:

Given, e = 0.78, Gs = 2.67

\(∴ {i_{cr}} = \frac{{{G_s} - 1}}{{1 + e}} = \frac{{2.67 - 1}}{{1 + 0.78}} = 0.938\)

∴ Option 4 is more appropriate.