Abstract: Based on 4 basic hypotheses, a generic Rankine theory is established and verified by idealized experiments. Its application in the foundation pit project in the Dongzhimen Station of the Beijing subway line No.13 also proves its effectiveness by predicting earth pressure which is very close to results obtained from field measurements. The generic Rankine theory establishes the relationship of the soil experimental indexes with its in situ ones, which allows the estimate of in situ active or passive earth pressure with experimental indexes. For the unsaturated soil, this method provides a very accurate estimate of earth pressure from the direct shear experimental indexes, which overcomes the shortage of the extended Rankine theory. The formula can appropriately utilize existing engineering experience and data, which is a new way to application of the soils mechanics for unsaturated soils in engineering.