According to the stress and strain condition of the soil around a pile,two formulas are developed based the extremum principle, with which the radius of plasticity area can be determined.

• 根据沉桩时桩周土体的受力及变位特性，文章运用了极值原理分别从静力学和考虑速度场两方面出发，推导并给出了桩挤土效应的计算公式。