交通荷载作用下饱和土-薄壁管桩体系的动力荷载传递机理研究

Thin-walled pipe piles have been widely used to reinforce the soft subgrade of road engineering in China’s South-East coastal areas, and the Yangtze river and the pearl river delta where there are rich and thick saturated soft soil layers. However, the dynamic load-transfer mechanism between the saturated soil and the pipe pile under traffic loads is not yet clear. To this end, in this project, the Boer’s porous medium theory and elastic shell theory are employed to describe the mechanical behavior of the soil and the pile, respectively, while the traffic load is treated as a moving time-harmonic load. By using the method of boundary integral equation, the rigorous theoretical models for the dynamic response of thin-walled pipe piles embedded in homogenous and multilayered saturated visco-elastic half-spaces are built, respectively. And the semi-analytical solutions of the effective stress, pore-liquid pressure, and displacement at the pile-soil interfaces are presented. With these solutions, the effect of the moving speed and vibrating frequency of the load, and the layered property of the soil on the dynamic response of the soil-pile system is studied. By employing a model mobile load simulator to simulate the traffic load, the model test for the mechanical behavior evolution at the interface of the soil and the pile subjected to the long-term effect of traffic loads is performed. Then the variation of the displacement, effective stress, and pore-liquid pressure at the pile-soil interfaces with different load times is studied, and also their correlation models are established. This study can reveal the dynamic load-transfer mechanism of saturated soils and pipe piles to traffic loads, and provide the scientific reference for the related engineering design and practice.

东南沿海以及长江、珠江三角洲等地区富含深厚饱和软土层，这些地区的道路工程建设广泛采用薄壁型管桩进行软土地基加固，但在交通荷载作用下饱和土和管桩的动力荷载传递机理尚未明确。本项目拟采用Boer多孔介质理论和弹性壳理论分别描述饱和土和管桩的动力学行为，交通荷载视为移动的稳态谐和荷载。采用边界积分方程法建立交通荷载作用下均质和层状饱和黏弹性半空间中薄壁管桩动力响应的严格理论分析模型，得到桩土接触面上有效应力、孔压、位移等的半解析解，在此基础上研究荷载移动速度、振动频率以及土体层状分布特性等对所得动力响应的影响；采用小型移动荷载模拟系统开展交通荷载长期作用下饱和土和管桩接触界面力学行为演变的模型试验，主要研究桩土接触面上位移、有效应力和孔压等动力响应随加载次数的变化规律，并建立其相关关系模型。研究成果揭示了交通荷载作用下饱和土和管桩的动力荷载传递机理，并为相关工程的设计和施工等提供科学依据。

东南沿海以及长江、珠江三角洲等地区富含深厚饱和软土层，这些地区的道路工程建设广泛采用薄壁型管桩进行软土地基加固，但在交通荷载作用下饱和土和管桩的动力荷载传递机理尚未明确。本项目采用Boer多孔介质理论和弹性杆振动理论分别描述了饱和土和桩基的动力学行为，将交通荷载视为稳态谐和荷载。首先考虑桩基的轴向和径向变形，通过叠加原理，提出了饱和土中桩基的动力响应积分解；然后推导得到了埋置荷载作用下刚性地基上有限厚度饱和土层的三维动力Green函数，为建立饱和土桩动力相互作用边界积分方程提供基本解；通过建立描述圆板和饱和土体动力相互作用的第二类耦合Fredholm积分方程，进而得到了饱和土层上刚性圆板的竖向动力柔度系数，为获得桩底土体反力提供基础；采用Hamilton动力学原理，建立了作为二维空心杆结构的管桩的控制方程，并推导得到了交通荷载作用下薄壁管桩竖向动力柔度的解析解，揭示了其动力荷载传递机理；最后结合饱和软土地基处理时桩基的工作环境，开展了桩基承载性能模型试验和浸水试验，揭示了长期浸水条件下其承载性能演变规律。成果丰富了桩土动力相互作用理论，对管桩复合地基的设计和工程应用具有重要意义。