基于摩擦学及颗粒流方法的粘性土中静压桩试验研究

The jacked pile has been applied widely due to high bearing capacity, environmental protection and showing the jacked load. With the improvement of the testing technology and the increase of the analytical methods, the research into the jacked pile is gradually furthered . Firstly, in this application, the full-scale pile tests, installing kinds of measured devices, are conducted at site covered by cohesive soil. Not only the axial force and end bearing resistance but also the side stress on the pile-soil surface and the pore water stress are measured at the same time, thus the effective side stress could be obtained. On this basis: (1) combining the adhesion- plough friction theory from tribology with three-stage sliding friction mode，the friction coming from pile driving are studied. (2) the cling coefficient is introduced so as to research the pile-soil interaction, and the bearing capacity development as well as it’s determination method is studied from a new perspective. (3) The particle flow method PFC2D test simulating the continuous penetration process of the jacked pile is carried out under the centrifuge model test condition, revealing the mechanism of the pressure between the pile and the earth at microscope level. Combined the high-reliability test data and the tribology analysis, the mechanism of jacked pile is discussed from both microscopic and macroscopic view, then giving a more reasonable way to determine the bearing capacity.

静压桩承载力高、保护环境且能显示压桩力，得到广泛应用。随着测试技术的提高和分析方法的创新，对静压桩研究逐步深入。. 本申请项目首先在粘性土场地上进行安装多种测试传感器的足尺管桩试验，在测试桩身轴力、桩端受力的同时，测试桩土界面的侧压力以及孔隙水压力，从而求得有效桩侧压力。在此基础上：（1）采用摩擦学的粘着-犁沟摩擦理论，结合三段式滑动摩擦模式对沉桩摩擦展开研究；（2）引入贴紧系数考察桩土作用，从一个新角度研究承载力发展变化和确定方法；（3）利用颗粒流PFC2D进行静压桩数值实验，采用类似于离心模型试验的原理解决重力失真问题。并通过参数标定、算式输入及结果验证，将高信度试验资料、摩擦学分析及颗粒流模拟联动结合，宏细观探讨静压桩受力机理，提出更加合理的承载力确定方法。

针对静压桩机理和细观层面的问题模糊不清，运用摩擦学机理、颗粒流仿离心模型数值试验及现场测试方法，研究结论对静压桩沉桩机理、承载力的确定以及数值仿真都有重要意义。本项目通过现场实测桩端力、压桩力、桩侧土压力以及孔隙水压力，确定了桩侧摩阻力分布。研究了粉土与粉质黏土互层中静压桩桩土界面径向土压力，发现沉桩过程中引起的总径向土压力随贯入深度增加逐渐增大，在沉桩过程中同一贯入深度，随桩身的贯入，桩侧总径向土压力存在明显的退化现象。采用极限平衡理论分析沿桩长方向不同深度的总径向土压力时，在粉土中需同时考虑孔隙水消散和不同剪切程度(H/D)对径向压力退化的影响，剪切退化系数为0.19；在粉质黏土中考虑不同剪切程度(H/D)对径向压力退化的影响，剪切退化系数为0.12。运用摩擦学理论，结合桩侧实测有效侧压力分布，解释了滑动摩擦的机理，提出了桩侧摩阻力的计算方法。利用黏着-犁沟理论分析了室内模型试验得到的不同壁厚、桩端形式和桩径的桩侧阻力和桩身单位侧摩阻力的变化规律，静压沉桩过程中桩土界面滑动摩擦属于湿摩擦，桩土之间泥浆液膜是引起“侧阻退化”的主要原因。黏着-犁沟理论分析了沉桩引起的桩侧阻力和桩身单位侧摩阻力模型试验结果，揭示了饱和黏性土中静压沉桩的力学机制.利用参数联动传递，实现了在粘性土中静压桩的颗粒流 PFC 数值试验模拟。为深入探讨层状黏性土中静压桩的贯入机制，结合离散元PFC2D软件在处理大变形、非线性等问题的优势，考虑到接触黏结模型对模拟土体的优越性，建立了静压桩贯入层状黏土中的离散元模型，实现了离散元中静压桩的贯入过程。桩径10 mm和15 mm 的分析结果与桩径为20 cm的规律性相一致。不同土层接触力链的分布形式不同，粉土层的接触力明显的大于粉质黏土层。研究结果有助于从细观层次上揭示层状黏土地基中静压闭口管桩的贯入机理。