A $2\mathrm{.}5m$ thick fill with large dimensions in plan is going to be placed over the ground,

the geotechnical profile of which is shown in Figure $3.$ As can be observed, ground

profile includes a soft clay layer $10m$ thick.

The results of site investigation suggest the possible existence of a continuous thin

sand layer at $6m$ depth. Nevertheless, to be on the safe side, it has been decided not to

consider its effect in the project estimate for the consolidation time.

In order to allow an earlier date of pavement construction on top of the fill, it is

decided to install PVD drains $($equivalent radius $=0\mathrm{.}10m),$ in a square pattern with

spacing of $2\mathrm{.}65m.$ Assume ${}_w=9\mathrm{.}8k\frac{N}{m}3.$

$($i$)$ Calculate the primary consolidation settlement, due to the construction of fill.

$($ii$)$ Calculate the average radial consolidation ratio expected after $6$ months.

$($iii$)$ At the end of six$-$month period, a surface settlement of $66mm$ registered.

Assuming that all parameters of the clay layer used in the computations are correct,

check whether that settlement value confirms that the thin sand layer works as a

draining boundary.