Consider a doubly$-$drained clay layer with a Cv of $1$ m$2/$yr and a thickness of $20$ m$.$ Calculate the time required for $70\%$ consolidation to take place. Compare this time to the time that it would require for $70\%$ consolidation to take place if thin sand layers were present at a depth $($from the top of the clay layer$)$ of $2$m$,5$m$,10$m$,$ and $15$m$.$ Report a time for each sublayer.