An full scale load test was performed on an isolated pile in order to aid prediction of the settlement characteristics of a pile group installed in the same ground conditions. It was observed that the single pile settled by $1$ mm under an applied head load of $400$ kN$.$ The following date are given: pile length L$=25$ m pile diameter d $=0\mathrm{.}6$ m pile elastic modulus Ep$=25$x$102$ MN$/$m$2$ soil shear modulus variation with depth G$=10+1\mathrm{.}2$z MN$/$m$2$ soil Poisson$$s ratio $=0\mathrm{.}2.$ A $10$x$10$ pile group consisting of piles identical to the one tested and spaced at $2$ m centres is to be installed in the same type of ground. Estimate the stiffness of the pile group, i$.$e$.$ the load required to make the whole group settle by $1$ mm