$\frac{20}{6}$

The soil profile shown below has a $15\text{'}$ thick clay layer below a $5\text{'}$ sand layer. The Poisson's Ratio of the clay is $0\mathrm{.}5$ and the Undrained elastic modulus of clay is $500ksf.$ A square rigid foundation is placed on the ground surface and carries a load $20$ kips. Maximum settlement cannot exceed $1"$ What is the minimum size $($in feet$)$ of the square footing?

$p_c=\frac{0\mathrm{.}5tsf}{21000}=1000PSF$

$e_0=0\mathrm{.}76$

$C_C=0\mathrm{.}31$

$C_R=0\mathrm{.}02$

$N_{\text{L}\text{O}\text{M}}=-20$

$(b)$

Size of footing