The equation hW=h ? Z, can be used to plot pressure net representing lines of equal water pressure without saturated soil mass since all three quantities in equation can be expressed a percentage of total hydraulic head H.

Both Bligh?s ory and khosla?s ory deals with a finding of uplift pressure and exit gradient.

According to commonly accepted ideas, undermining is supposed to result from piping, that is, erosion of sub-soil by high velocities of flow of water through it when such velocities exceed certain limit.

The direction of seepage is always perpendicular to equipotential line. But both equipotential line and stream line (flow line) is mutually orthogonal. So individual particle of water seep through stream line.

In earth dam with filter, base parabola does not cut d/s slope. But in earth dam with no filter, base parabola will evidently cut d/s slope.

The portion between any two successive flow lines is called a flow channel and portion enclosed between two successive equipotential lines and successive flow lines are known as field.

Given,
k₁=9×10^-7 cm/s
k₂=4×10^-7 cm/s
?₁=30°
since \(\frac{k_1}{k_2} = \frac{tan?_1}{tan?_2}\)
\(\frac{9×10^{-7}}{4×10^{-7}} = \frac{tan30}{tan?_2}\)
? ?₂=14.39°.

Since pressure is equal to force by area,
p_s =J/A
? J=p_s A.

According to practical suggestion given by A.Casagrande, every transition in shape of curve is smooth, being eir elliptical or parabolic in shape.

Given,
??=10.69 kN/m³
The critical hydraulic gradient i_c is given by,
\(i_c= \frac{??}{?_w}\)
\(i_c= \frac{10.69}{9.81}\)
? i_c=1.09.