本文在考虑桩-土相互作用的基础上，根据桩-土侧向变形协调及竖向变形相等的条件，应用弹性理论导出了线弹性状态下桩体及桩周土的应力-应变关系，得出了桩体材料屈服时桩-土应力比的计算式。利用摩尔-库仑屈服准则导出了桩周土处于极限平衡状态时，桩体和桩周土竖向变形的表达式，并导出了碎石桩极限承载力计算式。讨论了桩-土应力比、竖向应变与置换率及桩周土变形模量的关系。同时指出：用碎石桩加固软土地基其加固效果比较明显。但用碎石桩来加固土的变形模量大于8 MPa的地基，加固效果不很明显，且是十分有限的。并建议对于碎石桩加固的软土地基应该按控制沉降量设计法来代替传统的控制承载力设计法来进行设计计算。为验证本文方法的正确性，通过工程实例，将本文计算结果与实验结果进行了对比，对比表明：本文方法有较高的精度。

In this paper, based on the pile-soil interaction, equality of the vertical deformation and the harmony of the lateral deformation, the relationship of the stress and the strain of the piles and the pile lateral soil is derived by the elastic theory under the linear elasticity. The formula of pile-soil stress ratio at the pile materials yielding is obtained. The formulas of the vertical deformation in the piles and the pile lateral soil, the ultimate bearing capacity of the single pile arc derived by Mohr-Coulomb yielding condition at the ultimate equilibrium state. Relationships between the pile-soil stress ratio, the vertical deformation and the replacement ratio, the pile lateral soil modulus of deformation arc discussed. Meantime, it is indicated that the effectiveness reinforced by the crushed-stone piles in the weak ground is obvious, but it isn't obvious for the ground modulus of deformation to excess 8 MPa and the reinforced effectiveness is very finite. It is indicated also that the traditional design method of controlling bearing capacity should be replaced by the design method of controlling settlement to the weak ground reinforced by the crushed-stone pile. To verify the reliability of this method, the calculating results in this paper are contrasted with the test results by and engineering example and it is confirmed that the method has very high precision.