For a given soil profile, complete the following

$($a$)$ Calculate the drained shear strength on the horizontal plane A$-$A$.$

$($b$)$ Suppose the water level in the lake drops by $20$ feet due to lack of rainfall. What would the

drained shear strength on plane A$-$A be$?$

Fresh water lake

$20$ ft

$15$ ft

A $--$

Clay

Lake bottom

c$\text{'}=400$ psf

$\text{'}=26\backslash$deg

Ysat $=110$ pcf