Abstract: The soft soil foundations with dry crust are different from the homogeneous foundations. Due to the closure effect and stress diffusion of hard crust, the method for the plastic and critical loads of soft soil foundations is different from that for the homogeneous foundation. By using the unified strength theory of three shears to analyze and calculate the double-layer foundation and considering the influences of the closure effect and stress dispersion with the static lateral pressure coefficient, the formulas for the plastic and critical loads of hard-shell layer soft soil foundations are obtained. Meanwhile, by adjusting the coefficients b and c, the formulas for the bearing capacity of foundations under the unified strength theories of twin-shear and Mohr-Coulomb are obtained, and the three formulas are compared through examples. The results show that with the increase of the coefficients b, c and the static earth pressure, the bearing capacity of the foundation increases. The unified strength solution of twin-shear and Mohr-Coulomb solutions are divided into three shear unified strength solutions. The three-shear strength solution is more in line with the actual situation.