$(6)$ A retaining wall, A cantilever retaining wall of $7$ meter height retains sand. The properties of the

sand are: $e=0\mathrm{.}5,\frac{O}{?}=30$ and $Gs=2\mathrm{.}7.$ Using Rankine's theory determine the active earth pressure

at the base when the backfill is $($i$)$ dry, $($ii$)$ saturated and $($iii$)$ submerged, and also the resultant active

force in each case. In addition determine the total water pressure under the submerged condition.

$(15$ Marks$)$