On this foundation the article inducts in detail the method which is based on the relative settlement of calculating unit area end support ( qb ) force at the same time considering the feature of pedestal pile ' s " arch effect " the article introduces conception of pile effective length and finally obtain t he formula of calculating man - made pipe with bulb - shaped axial carrying capacity . the article uses marc program to calculate and analyze foundation soil ' s stress and displacement and gets the change curve chart and the proportion that is shared by king - pipe side soil friction resistance and pipe end counterforce respectively . the article inducts the structure of pedestal in detail on the basis of generalizing pedestal application cases of many countries 在此基础上论文详细归纳了以相对沉降为依据确定单位面积端承力q _ b的计算方法，并考虑扩底桩的“拱效应”特点引入了有效桩长的概念，最后结合公路规范推出了比较实用的人工挖孔扩底桩轴向承载力计算公式。论文运用了marc程序对地基土的应力和位移进行了有限元数值计算分析，得到了地基土的应力和位移场的变化曲线和在加载过程中桩侧土摩阻力和桩端反力各自所承担的比例；本文还在总结各国挖孔扩底桩应用情况的基础上就扩底桩的构造进行了详细的归纳。
