开口管桩沉桩过程试验研究与颗粒流模拟

Experimental and Numerical Analysis of Open-ended Pipe Piles During Jacking into Sand

利用侧面透明的模型箱和铝管半模桩模拟了开口管桩在砂土中的沉桩过程.分别测量了不同桩径和不同相对密实度开口管桩完全闭塞时的土塞高度.结果表明桩径越大,相对密实度越小,则土塞高度越大.利用高分辨率数码摄像设备观察到了土塞形成的三个阶段,重点分析了土塞内几个特征砂颗粒的移动轨迹和压桩过程中孔隙率和接触数的变化,从细观尺度出发探讨开口管桩沉桩过程中砂土的变形机制和土塞形成机理.利用Geodip软件分析了桩土接触面处的砂粒长轴定向和平均配位数,分析表明,土塞形成过程中颗粒原先的结构被打破以及发生了剧烈旋转,颗粒重新进行分布.在模型试验基础上,通过二次开发PFC2D颗粒流程序对沉桩全过程进行离散元仿真模拟.数值模拟结果表明,PFC2D能够模拟开口管桩从开始刺入砂土到形成土塞并最终呈现闭口管桩性态的整个过程.

The mechanism of soil plug formation and particles movement were analyzed from the meso-scale with physical model tests and numerical simulations. The container consisting of four steel sheets and one glass side and aluminum semi-model pile, was used to simulate the installation of open-ended jacked pipe pile in sand. The heights of soil-plug were recorded during the pile jacking into sand with different diameters and relative densities. The results show that, the larger pile diameters are, the higher soil-plug heights are; Conversely, the larger relative densities are, the smaller soil- plug heights are. The course of soil-plug formation was recorded from the transparent glass side and the process could be divided into three stages. Especially, the trails of some characteristic sand particles movement, porosities and contact numbers were analyzed emphatically. The major axis orientation and mean coordinate numbers of sand particles which located in pile-soil interface were analyzed with the software Gepdip. Results show that the original structure of particles are disturbed and rotated intensively, and the particles have been redistributed. Then, with the results of model test, the numerical model was established and the driving process was simulated, which could take both squeezing effects and plugging effects into consideration simultaneously. The behaviours of the numerical model are consistent with the results of physical model test. It indicates that PFC2D is capable of simulating the process of pile jacking into sand.