$($a$)$ Define the equation for determining the efficiency of a pile group and relate this to the importance of using piles driven in groups.

$[5$ marks$]$

$($b$)$ With reference to $($a$),$ draw the bulbs of pressure to differentiate between a single pile and a pile group.

$[8$ marks$]$

$($c$)$ Describe FOUR situations in which a pile system may be the preferred foundation option.

$[12$ marks$]$