Q$2$: Consider a $3$ by $3$ pile group in a layered saturated clayey soil, as shown in Figure $2.$ The solid piles are circular in cross section and have the same diameter D of $300$ mm $.$ The pile centre$-$to$-$centre spacing, d $,$ is $600$ mm $.$ The pile group is designed to support a vertical downward load of $1500$ kN $.$ Assume the lump$-$sum factor of safety for the load$-$bearing capacity of the pile group is $3.$

$[$Total: $30$ marks$]$

$($a$)$ Determine the vertical load$-$bearing capacity of an individual pile in undrained conditions.

$[10/30$ marks$]$

$($b$)$ Determine the vertical load$-$bearing capacity of the pile group in undrained conditions by assuming that the piles in the pile group acts as a block with dimension $\backslash ($ L$\_\{$g$\}\backslash$times B$\_\{$g$\}\backslash$times L $\backslash ).$

$[10/30$ marks$]$

$($c$)$ Does the pile group have sufficient load$-$bearing pile group capacity to support the vertical load?

$[3/30$ marks$]$

$($d$)$ To carry out pile$-$loading$-$tests on driven piles in clays, why should the pile$-$loading$-$tests be carried out at least a month after the pile installation?

$[3/30$ marks$]$

$($e$)$ List two disadvantages of bored piles in comparison to driven piles.