静压桩沉桩及已打入桩遮拦效应的数值模拟

采用三维有限差分软件 FLAC3D 建立了数值模型, 对比了圆孔扩张理论的解析解与数值解, 并在此基础上建立了桩实体单元基于位移贯入法模拟桩-土间摩擦作用, 且与相关文献中施加节点力模拟摩擦效应的方法进行了对比, 二者的计算结果较吻合. 基于此数值模拟方法 对静压桩单桩、双桩的沉桩过程进行计算分析, 并就已打入桩体对沉桩过程中土体位移的影响 进行研究, 得到以下结论: 模拟桩-土问摩擦效应的两种方法中, 位移贯入法计算所得土体水平位移在地表处较大, 这是因为桩体以固定速度向下运动时, 为阻止圆孔缩径而约束了其径向位移, 消除了摩擦效应对土体水平作用的影响. 沉桩结束后, 在大于地表下1/4 桩长深度范围内 的土体水平位移较大, 是主要的变形区域. 上部土体沉降较大, 而下部土体沉降较小, 其中距地 表下1/8 桩长至 1/4 桩长处沉降最大, 说明已打入桩的存在改变了土体水平位移的大小, 更使得土体水平位移随深度的变化趋于线性. 待打入桩的沉桩过程使得已打入桩身产生一定的倾斜. 由于沉桩扩孔的影响, 受到水平挤压的桩前土体在已打入桩的阻隔下沿着桩身向上隆起, 表明已打入桩的存在改变了土体位移的分布模式, 最终达到了减小水平位移的目的. 

Numerical Study on Statically Pressured Pile and Its Masking Effect of Driven Pile

This paper compares the analytical and numerical solutions of the cavity expansion theory based on calculations using the 3D finite difference software FLAC3D. By simulating pile-soil friction using the displacement penetration method, comparison of the result of applied nodal force is in good agreement with the literature. Based on the simulation method, calculation and analysis of the  static pressure single pile, double pile driving process, and impact on the displacement of the pile driving from driven pile, the following conclusions can be reached: The horizontal displacement on the surface is bigger. The
reason is constraintting the radial displacement when the pile body move downward at a constant speed which is in order to prevent the circular hole necking. After pile driving, the depth range of more than 1/8 pile length is the main deformation area, so the horizontal displacement is bigger. The upper soil subsidence is bigger than the lower region. The largest settlement appears below the surface by 1/8−1/4 of the pile length. Pile driving process makes the pile a bit tilt. Due to the impact of the pile driving reaming, the soil uplifts along the driven pile because of the pile barrier. This is the substance of the masking effect, achieving the purpose of reducing horizontal displacement by changing the distribution of soil displacement.