考虑土芯作用的大直径灌注筒桩轴向荷载传递性状分析

Analysis of axial load-transfer of large-diameter tubular pile using cast-in-situ concrete

大直径现浇混凝土薄壁筒桩为高速公路软弱地基处理中的一种新型高效优质桩。筒桩具有与一般的灌注或沉管实心桩不同的荷载传递机理,筒桩的荷载传递机理的复杂性制约了筒桩承载理论的发展与工程应用,其工程设计方法至今仍处于半理论半经验的状态。考虑大直径灌注筒桩土芯分担荷载以及筒桩与土芯内摩阻力发挥情况,采用一种桩内侧阻、桩外侧阻和桩端阻荷载传递模型,推导出一种沉管灌注筒桩的轴向荷载-沉降曲线的解析算式,并计算得到任意截面桩身轴力及内外侧摩阻力表达方程式。通过一工程算例,验证本文公式的实用性。计算结果表明,土芯分担顶部荷载并提供内侧摩阻力,对增大承载力和减小沉降量都有贡献。

Thin-wall cast-in-situ tubular pile is a new type of high quality pile, which has been applied in soft ground treatment. Load transfer mechanism of tubular pile is not expatiated completely because of the complex mechonism of soil core, which restricts the development of the theory for the bearing capacity of pile and its practiceal application. With linear elasto-plastic load transfer function, a set of analytical equations for the axial load-settlement curve of thin-wall cast-in-situ tubular pile were deduced. Correlative parameters of the pile-soil system could be got from fitting of measured P-S curve, and the distribution equations of axial force and friction along pile could be calculated. Case study was given to validate the method.