基坑开挖卸荷下桩基抗拔承载力影响因素研究

Study on influence factors of uplift pile bearing capacity under unloading of foundation pit excavation

目前关于抗拔桩的研究多以桩侧摩阻力反映桩的承载性状,对于桩侧桩-土界面法向压力研究较少.鉴于此,采用Plaxis 3D有限元软件,研究基坑开挖后桩的极限抗拔承载力、桩侧摩阻力等的变化情况.结果表明:对桩承载力而言,桩周土体的粘聚力和摩擦角影响较大;开挖的范围对桩的承载力影响较小,粉质黏土中基坑开挖宽度大于37.5倍桩径时,较未开挖时承载力损失比值为10.82%~17.83%,而砂土中基坑开挖宽度大于40倍桩径时,较未开挖时承载力损失比值为15.37%~33.01%;对桩-土界面法向压力曲线进行线性拟合并与未开挖状态下的斜率进行归一化分析,得到开挖后斜率与未开挖状态下的斜率比值,粉质黏土为9.18,砂土为34.92~40.94.

At present,the research on uplift pile mainly uses pile side friction to reflect the bearing behavior of pile,and there is little research on the normal pressure of pile-soil interface.In view of this,through the PLAXIS 3D,the changes of pile ultimate uplift bearing capacity,pile side friction,pile shaft axial force and pile normal stress after foundation pit excavation were studied.The results show that:for the bearing capacity of pile,the influence of cohesion and friction angle of soil around pile is great;the excavation range has little impact on the bearing capacity characteristics of the pile,for silty clay,when the width of the foundation pit excavation is greater than 37.5 times the pile diameter,compared with the non excavation,the loss ratio of bearing capacity is 10.82%~17.83%;for sandy soil,when the width of the foundation pit excavation is greater than 40 times the pile diameter,compared with no excavation,the bearing capacity loss ratio is 15.37%~33.01%.Linear fitting on the normal pressure curve of the pile soil interface and normalization analysis on the slope in the unexcavated state were performed and the ratio of the slope after excavation to the slope in the unexcavated state was obtained,which is 9.18 for silty clay and 34.92~40.94 for sandy soil.