Question

A 3 m thick soil stratum has coefficient of permeability $3\times {10}^{-3}cm/secat{25}^{\circ }C$. Test results on same soil gives porosity 30% bulk unit weight as 2 gm/cc and moisture content of 25%. The head at which upward seepage will cause quick sand condition is in m.

• A. 2.7
• B. 1.9
• C. 3.6
• D. 1.1

Answer 1

The correct option is A 2.7

$K=3\times {10}^{-3}cm/s$
At quick sand condition
$\gamma =2g/ccF=1$

$w=25\%n=30\%F=\frac{i_c}{i}=2\therefore i=i_c$

$\therefore e=\frac{n}{1-n}=\frac{0.3}{1-0.3}\frac{h}{L}=\frac{G-1}{1+e}$

$\therefore e=0.428$

$\therefore \gamma =\left(\frac{G+e.S_r}{1+e}\right){\gamma }_w$

$\gamma =\frac{G(1+w)}{1+e}{\gamma }_w$

$2=\frac{G(1+0.25)}{1+0.428}\times 1$

$G=2.285$

$G\simeq 2.29$

$\therefore h=\left(\frac{G-1}{1+e}\right)\times L$

$h=\left(\frac{2.29-1}{1+0.428}\right)\times 3=2.7m$