中文摘要：

基坑开挖引起的坑底土卸荷回弹会使既有桩基产生受拉的不利影响,而桩身拉力在中性点位置达到最大值。利用简化的附加侧摩阻力分布模型,对中性点的变化规律进行了理论分析,再结合相关的研究数据,通过汇总分析,得出了中性点深度随桩长、开挖深度、桩侧土体性质等因素的变化规律。分析显示,中性点深度与桩长的比值、开挖深度与桩长的比值近似满足线性正比关系,桩侧土体重度、内摩擦角的增加会引起中性点位置的下移,未设置围护结构、桩端扩底等条件也会引起中性点位置的下移。在此基础上,提出了预测中性点位置的计算模型,预测结果与数值分析结果较为吻合。

英文摘要：

Unloading and rebound of soil induced by excavation can result in an adverse effect on existing piles with the action of the tensile force, meanwhile the tensile stress of pile reaches the maximum at the neutral point. The variation of neutral point of the additional skin friction is analyzed theoretically with a＇simplified distribution model. The variations of the neutral point location with pile length, excavation depth and the properties of surrounding soil are obtained by summarizing and analyzing the reported data of pile foundation during excavation. The results show that there is approximately linear positive correlation between the ratio of neutral point depth to pile length and the ratio of excavation depth to pile length. The location of neutral point descends with increasing the unit weight and the internal friction angle of the surrounding soil. Similar downward movement of the neutral point can also occur in the case of the absence of retaining structure for excavation or the presence of expanded pile tip. Based on this, a calculation model is put forward to predict the neutral point location. The predicted result is close to the numerical result.