Abstract: Most of the formulas for foundation ultimate bearing capacity factor are still borrowing the results of Prandtl theory. Considering the difference of calculation models, Nc=(Nq-1)tanϕ is not true. And experiments have proved that the intermediate principal stress would produce some influence to strength of soil. The result derived from Mohr-Coulomb criterion formula doesn't consider the effect of intermediate principal stress which causes the conservative results. To solve these problems, according to ultimate balance theory and unified strength theory, the analytical formulas of ultimate bearing capacity with completely coarse foundation is studied. In the calculation process, the intermediate principal stress factors is considered which results in a higher ultimate bearing capacity of foundation. Thus, in the practical application, the bearing capacity of the material itself can be fully utilized.

Key words: completely coarse, unified strength theory, ultimate bearing capacity, analytical formula

摘要： ：目前大多数地基极限承载力系数公式仍借用Prandtl地基极限承载力的结论，而考虑到计算模型的差异，Nc与Nq之间并不存在Nc=(Nq-1)tanϕ的关系。且实验证明，中间主应力对土体的强度会产生一定的影响，而由Mohr-Coulomb准则推导出的公式并没有考虑中间主应力的影响，致使结果偏于保守。依据极限平衡原理，结合统一强度理论，研究在基底完全粗糙情况下极限承载力的解析解，并通过分析算例，验证了极限承载力解析解的合理性。结果表明在计算过程中加入中间主应力这一影响因素时地基的极限承载力会提高，从而在实际运用过程中充分发挥材料自身的承载能力。

关键词: 完全粗糙, 统一强度理论, 极限承载力, 解析解