At a construction site $3$m thick clay layer is followed by a $4$m thick gravel layer which is resting onimpervious rock a surcharge load of $2$SKN$/$m$^2$ is applicd suddenly at the surface of the ground $.$Thesaturated unit weight of soil are $19$kN$/$m$3$ and $20$ KN$/$m$\text{'}$ for the clay and gravel layers respectively.The water table is at the surface. draw the variation of stress.