Example $6\mathrm{.}5$: Water flows at the rate of $0\mathrm{.}09m\frac{l}{s}$ in an upward direction through a sand

sample with a coefficient of permeability of $2\mathrm{.}7{10}^{-2}m\frac{m}{s}.$ The thickness of the sample is $120$

mm and the area of cross$-$section is $5400m{m}^2.$ Taking the saturated unit weight of the sand as

$18\mathrm{.}9k\frac{N}{m^3},$ determine the effective pressure at the middle and bottom of the sample.