通过数学理论推导，给出了考虑静止土压力系数K₀≠1时的条形基础的地基临界荷载P_1/4，并与国标《建筑地基基础设计规范》（GB50007—2011）中相应公式（5.2.5条）进行了对比分析，认为国标公式过高估计了地基承载力，而本文公式相对较合理。当基础受力层范围内存在软弱下卧层时，国标中“5.2.7”条给出了软弱下卧层承载力验算公式，但未说明软弱下卧层埋深超过多少时可不考虑软弱下卧层影响，采用已推导的地基承载力公式，通过无量纲化推导计算，给出了软弱下卧层相对临界埋深(H_cr/b)与基础相对埋深(d/b)之间的关系式。最后通过实例计算，得出了不同基础宽度、不同软弱下卧层抗剪强度指标下的相对临界埋深(H_cr/b)关系曲线，认为软弱层抗剪强度指标越大、上层土内摩擦角越大，则软弱下卧层相对临界埋深H_cr就越小，其不利影响就越小。

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.   