For a sheet pile wall given in Figure $1,$

a$.$ Determine the quantity of seepage under the piling. $(5$ Marks$)$

b$.$ Determine the factor of safety against 'boiling' at the surface $x-x\text{'}($Assume that the failure due to boiling takes place within a distance $\frac{D}{2}$ from the sheet piles; $D$ is the depth of penetration of the sheet pile$).(15$ Marks$)$

c$.$ Calculate the pore$-$water pressure at points a$,$ b$,$ c and d$.(10$ Marks$)$