Question

To provide safety against piping failure, with a factor of safety of 5, what should be the maximum permissible exit gradient for soil with specific gravity of 2.5 and porosity of 0.35 ?

• A. 0.155
• B. 0.167
• C. 0.195
• D. 0.213

Answer 1

The correct option is C 0.195

Specific gravity,

$G_s=2.5$

Porosity n = 0.35

Void ratio,

$e=\frac{n}{1-n}=\frac{0.35}{1-0.35}$

= 0.538

Critical hydraulic gradient,

$i_{cr}=\frac{G-1}{1+e}=\frac{2.5-1}{1+0.538}$

= 0.975

Permissible exit gradient (i) with factor of safety = 5 is

$i=\frac{i_{cr}}{5}=\frac{0.975}{5}$

= 0.195