Question

Consider the following statements:

Which of these statements are correct?

• A. 1, 2 and 3
• B. 1 and 2 only
• C. 2 and 3 only
• D. 1 and 3 only

Answer 1

The correct option is A 1, 2 and 3

The ratio of the ultimate load capacity of the pile group, $Q_{ug}$ to the sum of the individual load capacities of the pile in the group, is called group efficiency $\eta$.

$\eta =\frac{Q_{ug}}{n{Q}_u}$

Disturbance of soil during installation of piles and overlap of stresses between adjacent piles may cause the group capacity become less than the sum of the inidividual capacities, that is $\eta <1$. Generally, for smaller spacings between piles, $\eta <1$ .For larger spacing , the effect of pile interaction diminishes and $\eta$ approaches unity. In driven piles where the soil around the piles gets densified, as in loose to medium sand, $\eta$ may be even more than 1.