Abstract：Engineering practices and model test results all indicate that overburden soil stratum is often able to withstand greater head pressure than the pressure of its own weight. Currently，no relevant theory can explain this phenomenon. The concepts such as generalized buoyancy，generalized buoyant unit weight and generalized hydraulic gradient are proposed by considering adsorptivity of soil particles to pore water as well as considering connectivity of bound water；and then specific calculation method is given，explaining the physical meaning of the parameters such as ， and used in the calculation and recommending the estimating method of . The tests envisaged on measuring and are also given，then the relationship between and initial hydraulic gradient is established. Aforesaid calculation method takes the different natures of soil into account. For sand and loose soil，generalized buoyancy，generalized buoyant unit weight and generalized hydraulic gradient are changed into Archimedes buoyancy，traditional buoyant unit weight and hydraulic gradient. Further，calculation method of seepage force in different soils has been given. In the end，the unified expression of failure conditions of soil under the action of groundwater is got，which can interpret several different failure modes of soil under the action of groundwater. According to this theory，the calculating method of anti-seepage stability and the stability of resistance to the confined water of foundation pits should be amended and the current calculation method can only be applied to sand and loose soil. Some conclusions derived by using this calculation method to analyze the stability of soil in groundwater under different strata combinations are different from traditional arguments. For example，when analyzing the embedment depth of enclosure structures，if there is no impact of confined water，the seepage failure of the foundation pit is difficult to occur in the clay stratum and the ability of foundation pits to resist seepage failure in the silt stratum is better than that in sand layer. When analyzing the anti-upbursting of confined water in foundation pit，the traditional ballast-balance calculation is unsafe to the overburden soil stratum with permeability，while for the overburden soil stratum of confined water stratum containing a certain amount of silt，its ability to resist the confined water pressure is relatively increased. Finally，based on the result of the paper，the unified calculation theory on soil-water pressure is amended.
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2013, Vol. 32 
