Q$-2(10$ Points$)$

A $2m$ wide continuous foundation is placed at $D_f=1m,$ within a $1\mathrm{.}5m$ thick sand layer that is underlain by a weaker clay layer. The soil properties are as follows:

Upper sand layer : Unit weight, $=18k\frac{N}{m^3}$ and ${}^{\text{'}}=38$

Lower clay layer : Unit weight, $=19k\frac{N}{m^3},$ and Cohesion $($C$)=25K\frac{n}{m^2}$

Determine the maximum wall load that can be allowed $(Q_{\text{a}\text{l}\text{l}})$ on the foundation with $FS=3.$