砂土地层钉形变径桩变截面处端阻计算方法研究

Study on the Tip Bearing Capacity at Variable Section of Nail Shape Pile in Sand stratum

变径桩具有承载力高、施工速度快以及经济性强等特点,被广泛运用于铁路桥梁基础中。然而,现有桩基承载力计算方法主要针对等直径桩基,未能考虑变径截面带来的影响。由于桩基变径截面的存在,其竖向承载机制区别于普通的等直径单桩。采用有限元分析方法,分析竖向荷载作用下,砂土地基中钉形变径桩在变截面处的承载模式。计算结果表明:变截面以下有限范围内的土体存在刚性核,与变截面共同承担上部荷载;与普通等直径桩相比,变截面桩的桩身轴力在变截面处出现明显的突变现象;依据球孔扩张理论,引入变截面处承载力的计算公式,结合传统的桩基端阻与侧阻计算原理,推导了变径桩的竖向承载力计算公式。与现有规范对比表明,提出的公式可较好地计算砂土地基中变径桩的竖向承载力。

The variable diameter pile has the characteristics of high bearing capacity,fast construction speed and strong economy,and is widely used in the foundation of railway bridges.However,the existing pile foundation calculation methods are mainly based on equal-diameter pile foundations and fail to consider the influence of variable diameters.Due to the existence of variable cross-section,its vertical bearing and horizontal bearing mechanisms will be significantly different from ordinary equal-diameter single piles.In this paper,the finite element analysis method is used to discuss the bearing mode of the nail shape pile in the sandy foundation at the variable section under the vertical load.The soil in a limited range below the variable section has a rigid core,which shares the upper load with the variable section.Compared with ordinary equal-diameter piles,the axial force of the pile body of the variable-section pile will have obvious mutation phenomenon at the variable-section.According to the theory of spherical hole expansion,the calculation formula of the bearing capacity at the variable section is introduced,and the calculation formula of the vertical bearing capacity of the variable diameter pile is deduced based on the traditional calculation principle of the end resistance and side resistance of the pile foundation.The comparison with the existing codes shows that the proposed formula can better calculate the vertical bearing capacity of variable diameter piles in sandy soil.