开挖卸荷桩土界面荷载传递模型的修正与验证

Improved hyperbolic model of load-transfer for pile-soil interface and its verification considering deep excavation

为了准确预测深开挖条件下桩基的承载变形性状,在桩土界面荷载传递计算模型中考虑了卸荷效应.基于快速拉格朗日法(FLAC3D),将线弹性-完全塑性的桩土界面荷载传递模型修正为双曲线计算模型,修正后的模型可以考虑开挖卸荷后桩周土体法向应力减小对桩土界面剪切刚度的影响,也可以考虑开挖深度、面积和桩长对桩端阻力的影响.利用修正模型对开挖条件下砂土地基中的单桩进行了足尺数值试验,分析计算了开挖后桩基的承载性能,并将修正后模型的计算值与软件内嵌的线弹性-完全塑性模型的计算值及试验值进行对比分析.结果表明:修正后计算模型和传统计算模型都能够较准确地预测开挖条件下桩基总极限承载力,但是,修正计算模型考虑了支护结构外围土体对桩端承载力的贡献,能更准确地预测桩身下部侧摩阻力与桩端阻力.因此,修正计算模型更适合开挖条件下的桩基承载力计算.

An improved hyperbolic model of load-transfer for the pile-soil interface under deep excavation conditions was developed. It not only considered the influence on the initial shear stiffness because of excavation which decrease the normal stress of the surrounding soil, but also considered the influence of excavation depth, width and length of pile. A full-scale numerical experiment was completed on a single pile in sandy soil after excavation and the bearing capacity of pile foundation was analyzed using this model, and then the results was compared with the measurement and the calculating values, which were calculated from the traditional model. It was shown that the ultimate bearing capacity of pile foundation after excavation, which was calculated from both model, are closed to measurement. The tip resistance and shaft friction on the bottom of pile calculating from traditional model which cannot consider the contribution of soil for the pile tip behind the supporting structure, however, have significant differences compared with the measurement. So, the improved model is better to estimate the shaft friction and tip resistance for the pile foundation after excavation.