Dewatering of fine grained cohesive soil can be done only electro-osmosis method.

For fine-grained soils, the well point system can be extended by the vacuum method.

A flow net can be utilized for determination of seepage, seepage pressure, hydrostatic pressure, and exit gradient.

Where the dewatering system consists of a number of closely spaced well points or wells a simplified solution can be obtained by considering the lines of wells equivalent to a linear drainage slot.

Fully penetrating slot is used for both confined and unconfined case of flow.

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

EA= extra length factor, which is a function of the ratio of slot penetration p to the thickness of pervious stratum b.

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

The seepage analysis is done on the assumptions that the flow is laminar and Darcy’s law is valid and further assumed that the soil to be dewatered is homogeneous and isotropic.

ie =Δ h /l, represent gradient formula where Δ h=potential drop and l is the average of last field in the flow net at the exit end.