Based on the unified strength theory

a new formula of critical edge pressure and critical load of subsoil considering the effect of intermediate principal stress ?2 and the static lateral pressure coefficient is deduced. After contrasting the results of the unified solutions with those based on the Mohr-Coulomb criterion

it is shown that this method can reflect the essentials of foundation bearing capacity more accurately and be conducive to make full use of the strength of foundation. A thorough study of the intermediate principal stress coefficient b has been made through statistical analysis for 177 groups of soil indices and the loading test data of different foundation soils in Hebei province. The result proves that the value of b changes from 0 to 0.50 for the silt and clay soil foundation; and the relative error between the theoretical values of the foundation bearing capacity and the measured values of loading test is generally less than 5%.