Electro-osmotic method is used when co-efficient of permeability lies between 10-7 cm/see to 10-5 cm/sec. In electro-osmotic method, two electrodes are driven into the saturated cohesive soil. The cathode is made out of steel in the form of a well point or a tube. A steel rod or a pipe or a sheet piling is made to serve as anode as shown in Fig.1.
In general the surface of soil is negative charged and is surrounded by polar water and ions of other elements. When a current is passed through the soil, the positively charged ions on the surface are attracted towards cathode. During ellectro-osmosis process the attracted positively charged ions take the water of the double layer with them. The direction of flow is reversed and water is collected in the well point made of cathode. The collected water is pumped out.
Electro-osmosis method requires specialized equipment and high electricity consumption. Hence drainage from electro-osmosis is costly. This method should be used for exceptional cases when other methods cannot be used.