Question

At a site where sand deposit extends to a great depth, the ground water table is lowered from 2 m below G.L to 3 m below the G.L. The increase in effective stress is
$({\gamma }_d=16kN/m^{3}and{\gamma }^{\prime }=10kN/m^3)$

• A. $16kN/m^2$
• B. $10kN/m^2$
• C. $26kN/m^2$
• D. $6kN/m^2$

Answer 1

The correct option is D $6kN/m^2$


$\sigma =2{\gamma }_d+1{\gamma }_{sat}$ ${\gamma }^{\prime }={\gamma }_{sat}-{\gamma }_w$

$=2\times 16+20$ $10={\gamma }_{sat}-10$
$=52kN/m^2$ $20={\gamma }_{sat}$
$u=1{\gamma }_w$
$10kN/m^2$

${\sigma }^{\prime }=\sigma -u=52-10=42kN/m^2$


$\sigma =3{\gamma }_d=3\times 16$

$=48kN/m^2$

$u=0$
${\sigma }^{\prime }=\sigma -u=48-0=48kN/m^2$

Increase in effective stress =$48-42=6kN/m^2$