Q$.2(25$ marks$)$

In a $16(4x)$ piles group, the pile diameter is $0\mathrm{.}4m$ and center to center spacing of piles in the square group is $1\mathrm{.}5m.$ If $C_u=50k\frac{N}{m^2},$ with neglecting the bearing at the tip of the pile, determine whether the failure would occur as block failure or when the piles act individually. The piles are $12m$ long. Take $=0\mathrm{.}7$ for shear mobilization around each pile. Also determine the safe load on this group assuming the factor of safety $=2\mathrm{.}5.$