The maximum value of effective stress in the past divided by the present value, is defined as over consolidation ratio (OCR). The O.C.R. of an over consolidated clay is

If N_{f}, N_{d} and H are total number flow channels, total number of potential drops and total hydraulic head differences respectively, the discharge q through the complete flow is given by (where K is a constant)

A flow line makes angles θ_{1} and θ_{2} with the normal to the interface of the soils having permeabilities k_{1}, k_{2} before and after deflection. According to the law of deflection of the flow lines at the interface of the dissimilar soils