Abstract: In this paper,based on the effective consolidation stress concept,the equations of active and passive earth pressure for clay have been derived through the parameters c cu and φ cu  obtained from the conventional undrained triaxial compression test of consolidated samples.As a result,the formula for passive earth pressure is essentially the same as the traditional one,but the newly obtained coefficients for active earth pressure are much lower than the correspondent values from Rankine theory.In addition ,it has been proved that even for the total strength theory,the full pore water pressure must be taken into account in the earth pressure calculation.