Question

A group of a 16 piles (4 in each row) was installed in a clay deposit shown below. The diameter of each pile is 0.5m and clear spacing between the pile is 0.5 m. The depth of the pile group is 18m.

Group efficiency of pile group will be

• A. 60%
• B. 75%
• C. 90%
• D. 92.8%

Answer 1

The correct option is D 92.8%

$Q_u(g{)}_1=q_p\times A_g+\alpha \times P_g\times D$

$=9\times 25\times (3.5\times 3.5)+1\times 25\times (4\times 3.5)\times 18$

$Q_u(g{)}_1=9056.25kN$

$Q_u=9\times 25\times \frac{\pi }{4}(0.5{)}^2+0.8\times 25\times (\pi \times 0.5)\times 18$

$Q_u=44.15+565.2$

$Q_u=609.35kN$

For 16 piles

$Q_u(g{)}_2=9754.64kN$

Safe Load = $\frac{\text{Lesser of}{Q}_u\left(g{)}_{1}and{Q}_u\right(g{)}_2}{F.O.S.}$

Safe Load = $\frac{9056.25}{2.5}$

= 3622.5 kN

Group efficiency

${\eta }_g=\frac{Q_u(g{)}_1}{Q_u(g{)}_2}=\frac{9056.25}{9754.64}$

${\eta }_g=92.8$%