注浆成型螺纹桩抗拔承载特性的数值分析

注浆成型螺纹桩为一种利用施工工艺创新，结合钻孔灌注和二次注浆技术的新型螺纹抗拔桩型，目前已在软土地区开展应用。为了对其受力承载特性深入研究，使该桩型得到广泛推广，通过数值分析方法对其抗拔性能和承载机制进行了三维有限元数值模拟。首先，通过数值模拟桩-土界面室内大型直剪试验得到了有限元分析需要的桩-土接触面参数，而后将得到的参数带入注浆成型螺纹桩抗拔三维有限元数值模型，通过计算得到了不同距径比S/D（即螺距与桩径的比值）螺纹桩的抗拔荷载-位移曲线和轴力分布，并观察了抗拔过程中桩周土体塑性变形的发展。数值分析表明，螺纹桩与桩周土体的机械咬合作用增大了桩侧摩阻力，从而使桩体极限抗拔承载力较等截面圆桩提高约2～5倍；同时，其承载能力与桩体的S/D有关，当S/D取最优时，荷载-位移曲线的初始切向刚度最大，极限承载力最高，桩周土体形成的连续拱形破坏区域最大。

Numerical analysis of grouting-screw pile uplift bearing capacity

Grouting-screw pile is a new type of uplift pile which uses a construction technology innovation combining boring and secondary grouting, has been carried out in soft soil area. In order to conduct a further research on its bearing characteristics, so that the pile can be widely promoted, a three-dimensional finite element numerical simulation analysis of its uplift bearing performance and mechanism is carried out. Firstly, the numerical simulation of pile-soil interface indoor large direct shear test is done to get the pile-soil interface parameters. Secondly, the three-dimensional finite element numerical simulation analysis is done by using the pile-soil interface parameters obtained. Finally, through the numerical simulation, the uplift load-displacement curve and the distribution of axial force of screw piles for different values of S/D (ratio of screw pitch to pile diameter) are obtained; the development of plastic deformation of soil around the pile is observed. Numerical analysis shows that owning to the increase of skin friction of pile caused by the "mechanical occlusion effect", the ultimate uplift resistance bearing capacity of screw pile increases by 3~5 times than circular cross-section pile's; the bearing capacity is related to S/D, when the S/D equals optimum, the initial tangential stiffness of the load-displacement curves, the ultimate bearing capacity and the continuous arched plastic deformation zone of soil around the pile equal maximum.