$6\mathrm{.}2.$ An $8m$ thick clay stratum lies between a $10m$ thick sand stratum

at top and a rock layer at bottom. The unit weight of sand is $1\mathrm{.}75t^3.$ The

clay stratum has the following properties:

$L.L.=42\%,w=28\mathrm{.}5\%,G=2\mathrm{.}72$

A raft footing of $15m15m$ area and carrying a uniformly distributed

load of $20\frac{t}{m^2}$ is proposed to be constructed at the site. Determine the prob$-$

able consolidation settlement of the footing. The clay layer should be divided

into four sub$-$layers of equal thickness and the stress increments may be

computed by $2$:$1$ dispersion method.