Q$2$: Solve only one

a$)18m$ wood pile is installed small end down in clay$($see Fig a$).$ Pile diameter is $125mm$ at the end and $10m\frac{m}{m}$ increase in diameter. The undrained shear strength of the soil, measured from the pile cut$-$off level is: $0-6$ m$=12kP6-12m=16$kPa $12-18m=19$kPa. Determine the ultimate load capacity of the pile. Pile cut$-$off level is $1\mathrm{.}5m$ from the ground level. $Rd=1\mathrm{.}7.[20$M$]$

b$)$ The pile center to center spacing$($see Figure b$)$ in $x-$ and $Y-$direction is $1\mathrm{.}5m$ and $2m$ respectively design pile cap?$[20$M$]$