考虑软土结构性损伤的柱形孔扩张理论分析

采用考虑结构性损伤的四折线应变软化模型，针对管桩沉桩过程中产生的挤土效应，得出改进的柱形孔扩张理论解，并与已有模型进行对比分析，结果表明，简化的四折线模型与软土的典型压缩曲线最为接近，提出了四折线模型中各直线段和相应参数的确定方法。采用Mohr-Coulomb屈服准则和相关联流动法则，提出了桩周不同区域内土体的应力、应变计算公式，给出了极限软化半径、极限破坏半径和极限扩张压力的计算方法。结合工程实例，通过对比分析发现，四折线模型的位移计算值与实测值最为接近，能更好地符合管桩挤土效应的实际情况。

Analysis of cylindrical cavity expansion theory considering damage of soft soil structure

Using four-fold line strain softening model which considers the structure damage,according to the effect of squeezing soil when pipe sinking,the improved cylindrical cavity expansion theory is deduced;and it is compared with the existing models;the results indicate that the simplified four-fold line model is proximate with the typical compressing curve;and the method for determining each line and relevant factors is put forward.The formulas of stress and strain for each region around pile and the method for determining ultimate softening radius,ultimate destructive radius and ultimate expanding press are obtained by using Mohr-Coulomb yield criterion and associated with flow rule.On the basis of engineering case study,the improved cylindrical cavity expansion theory using four-fold line strain softening model is compared with the existing models;the results indicate that the displacement calculation of four-fold line model is the closest to the measured value;so the model can satisfy the practical engineering of squeezing soil more effectively.