Solution From Example Problem 8.11, turning the rectangular foundation into an equivalent round foundation:B =2r=28 m or r =14 m
Calculating the increase in stress to the top of the clay layer, use H =10 m
a =r/H =14/10 =1.4
Entering the upper part of Fig.4.16 with k =10,extrapolating between the a=1 and a=2
curves, the value of (I)(H/r)2= 0.24
I=(0.24)/(H/r)2 =(0.24)/(10/14)2 =0.47