Abstract: There has been controversy concerning the methods of estimating water and earth pressures together. This article quantitatively analyzes the error of existing methods of water and earth pressures calculation for the normally consolidated saturated clay under fully undrained or steady flow conditions. In most cases, the predicted results by existing methods were found non-conservative and errors can be over 40%. After that, the formulas for estimating the water and earth pressures together for both the normally consolidated and over-consolidated clay were derived using principle of equivalence. The results of proposed equations are found in consistent with those by WEI Ru-long. The formulas are also verified by method using undrained shear strength used by other scholars in foreign countries with good agreement. The proposed approach tends to overestimate the total pressure of water and earth pressure in both normally consolidated and lightly overconsolidated clay subject to steady flow. On the other hand, this approach may underestimate the total pressure in heavily overconsolidated clay. The critical state occurs when the negative excess pore pressure fully dissipates. The developed equations calculate the total active or passive pressure of saturated clay under fully undrained condition using of the total stress parameters. The formulas do not consider the influence of seepage on water and earth pressure. The significant impact of seepage on the water and earth pressure suggests it should be considered in engineering practices.

Key words: estimating water and earth pressures separately, estimating water and earth pressures together, the equivalence principle, loss rate of hydrostatic pressure, error