The standard formula for calculating the soil shear strength of the preloading ground under anisotropic consolidation is not applicable to isotropic consolidation process. In this paper

a new formula was proposed to calculate the soil shear strength of the preloading ground under isotropic consolidation process. This new formula was derived by analyzing the calculation principle of the two existing fundamental methods

which are effective stress method (ESM) and effective consolidation stress method (ECSM)

respectively. Then the results that calculated by the new formula and the standard formula applied to vacuum preloading and vacuum combined surcharge preloading were theoretically discussed and compared. Finally

the applicability of the new formula and the standard formula were tested by the practical engineering

and the difference between the calculated strength and the measured strength were also analyzed. The results show that the ECSM can be applied to the preloading ground under both the isotropic consolidation and the anisotropic consolidation

while standard formula is only applicable to surcharge preloading ground theoretically. The values of soil shear strength of the vacuum preloading and vacuum combined surcharge preloading that calculated by the standard formula are smaller than those calculated by the new formula. The relative difference of the two calculation values only relates to the friction angle and increases as the friction angle increases. In the vacuum combined surcharge preloading treatment project

the shear strength prediction values by the new formulas are closer to the measured values than those by the standard formulas. The result of this study can be potentially helpful for calculating different kinds of preloading grounds in practice.