Question

Increasing the depth of foundation in saturated clays results in an increased ultimate bearing capacity of strip footings

• A. Because the bearing capacity factor, $N_q$, decreases.
• B. Because the bearing capacity factor, $N_c$, increases as the depth increases.
• C. The term in the bearing capacity equation,$q{N}_q$, increases with depth.
• D. Because the angle of internal friction decreases as the depth of foundation increases.

Answer 1

The correct option is C The term in the bearing capacity equation,$q{N}_q$, increases with depth.

As per Terzaghi's theory,

$q_u=C{N}_c+q{N}_q+\frac{1}{2}B\gamma N_{\gamma }$ .... (i)

For Clay
$N_c=5.7$
$N_q=1$
$N_{\gamma }=0$

From (i)
$q_u=5.7c+q$
$=5.7c+\gamma D_f$

Hence,
Ultimate bearing capacity for strip footing increases with depth because
$q{N}_q=\gamma D_f{N}_q$,
increases with depth.