基于薄层单元法的单桩挤土效应数值模拟

通常预制桩施工会产生挤土效应, 这会对周围环境产生不利影响. 根据某桩基工程施工的实际情况, 利用大型有限元分析软件Abaqus, 通过在桩土间增加薄层单元的方法对单桩施工的挤土效应进行了数值模拟. 薄层单元的厚度取0.08 m, 其力学性质参数介于桩和土之间. 模拟时, 薄层单元近土侧与土中节点进行位移耦合, 而近桩侧则采用摩尔-库伦(Mohr-Coulomb)定律来反映桩体和单元之间的接触关系. 通过数值模拟, 探讨了外部荷载作用下抗压桩的变化特点, 得到了桩顶的荷载与桩入土深度的关系曲线, 分析了打入桩施工的有效影响距离和有效影响深度, 对比研究了有限元数值模拟结果与圆孔扩张理论的解析计算结果. 数值模拟结果表明, 单桩施工的水平向有效影响范围大约为5 倍桩径, 竖直向约为2 倍桩长. 数值模拟结果和解析计算结果比较接近. 使用薄层单元法进行打桩挤土效应数值模拟, 符合桩基工程施工的实际情况, 反映了桩土接触面的变形机理与受力状态. 这对桩基工程设计和施工具有一定的参考价值.

Numerical Simulation of Compaction Effects of Single Driven Pile Using Thin-Layered Element Technique

Compaction effect usually occurs in the construction of precast piles. This effect may have a negative impact on the environment. A pile-soil model is simulated based on a numerical method using the finite element software Abaqus. A specially-defined contact element of pile-soil interface is used with a thickness of 0.08 m to simulate the mechanical features of the interface between the pile and soil. The mechanical parameters of the elements are set between those of the pile and soil, and the elements close to the soil are coupled with the element nodes in the soil. The Mohr-Coulomb’s law is applied to reflect the constitutive law of the elements close to the pile. Based on the numerical simulation, the effective distance and depth resulting from pile driving
are analyzed. The characteristic change of the compressive pile is explored. The relationship between the load and the penetration depth together with the side resistance distribution of the pile are then obtained. The results of simulation and cavity expansion theory are compared. It shows that the effective horizontal and vertical distances are about 5 and 2 times the diameter of the pile, respectively. The described method may provide references to the construction and design in the pile engineering.