Abstract: Mathematical inferential reasoning was employed to obtain the critical load P_1/4 of strip foundation when  the effect of K₀≠1 was considered, and the obtained formula was compared with formula 5.2.5 in Code for Design of Building Foundation  (GB50007—2011). It's believed that the formula in the Code overestimates the foundation's bearing capacity while the formula in this study is more reasonable. When weak substrata exists in the foundation's load carrying layers, a check formula for the bearing capacity of the weak  substrata is given in "5.2.7" in the Code, but the Code doesn't explain under what embedded depth of weak strata  the effect of K₀≠1 can be ignored. On the basis of the obtained formula of foundation's bearing capacity, the relationship between the relative critical embedded depth (H_cr/b) of weak  strata and the relative embedded depth of foundation (d/b) was obtained through dimensionless calculation. Finally through calculation examples, curves of relative critical embedded depth (H_cr/b) with different foundation widths and different shear strengths of weak layer were acquired. It's concluded that when the shear strength of weak strata and the internal friction angle of topsoil are larger, the relative critical embedded depth of weak  substrata H_cr is smaller, hence the adverse impact would be smaller.       

Key words:  foundation's bearing capacity, coefficient of lateral earth pressure, weak substrata, critical depth of weak strata