由于水、土压力合算法存在一定的争议，首先对国内现行水、土压力合算公式在完全不排水条件和稳定渗流情况下计算正常固结黏土水、土压力的误差进行了定量的分析，发现计算结果在大多数情况下偏危险，误差可超过40%；然后根据等效原则，推导出了饱和正常固结黏土和超固结黏土的水、土合算公式，得到的公式与文献[2]建议的公式一致，同时证明了该公式与国外采用固结不排水抗剪强度的水、土压力合算公式也一致；对于正常固结和轻微超固结饱和黏土，由等效原则得到的水、土压力合算公式高估存在渗流时主动极限平衡状态水、土压力的合力，而对于重度超固结饱和黏土，水、土压力合算可能低估存在渗流时主动极限平衡状态水土压力的合力，最危险的状态是负超静孔压完全消散时。水、土压力合算公式是采用总应力指标计算在假定完全不排水条件下饱和黏土进入主动或被动极限平衡状态时的水、土总压力，公式并不能考虑渗流对水、土压力的影响，而渗流对水、土压力的影响显著，在实际工程中应加以考虑。

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.