中文摘要：

柔性基础、垫层、复合地基、下卧层土体的共同作用一直没有得到较好的考虑。将四者作为一个共同作用的系统，假设桩土界面之间存在相对滑移且同一水平面上地基土沉降不同，考虑系统四部分界面上的应力与变形协调，对典型单无体建立荷载传递基本微分方程并给出其解答，从而得到表征复合地基性状的沉降和桩土应力比等的求解公式；与某工程实测成果及按现行规范推荐方法计算所得结果对比表明该解答是合理的，柔性基础下桩体复合地基中的桩士荷载分担比、荷载传递机制等均与刚性基础下的复合地基不同，工程设计中要高度重视和运用等沉面和中性面的概念；最后对进一步的解析法研究提出了建议。

英文摘要：

Interactions among flexible foundation, cushion, composite ground, and underlying soils have not been well researched. A simplified analytical model is presented considering the above four parts as an interactive system. The method allows the relative movement between piles and soils, and assumes different settlements of foundation soil at the same level plane. The force equilibriums of a typical element are established. And then, according to the compatibility of stress and deformation on the interfaces between these four components, the formulas for settlement and stress ratio of pile-soil, which are used to characterize the behaviors of the composite ground, are derived. Comparisons demonstrate that the results from this solution are in accordance with the measured ones of a project in China＇s Zhejiang Province, and they are closer than those obtained using the recommended method of the current codes in China. The pile-soil load ratio and the load transfer law of pile composite ground under flexible foundation are different from those of rigid foundations. More attentions should be paid to the concepts of equal settlement plane and neutral point plane for the engineering designs. Finally, same suggestions are proposed for further study of analytical method of pile composite grounds under flexible foundation.