反拱曲面异形桩异形效应理论分析及透明土模型试验研究

The abnormal pile with inverted arch surface changes the traditional concept which means that the pile shape is circular, otherwise square. There are inward-concaved and inverted arch surfaces along the pile circumference. Two popular abnormal piles with inverted arch surface are the Y-section and X-section piles, both of which have been widely applied in the soft soil treatment in the highways of Zhejiang and Jiangsu and have been incorporated in the relevant national and local standards. The engineering practices show that the economy and bearing capacity of abnormal piles with inverted arch surface are significantly better than those of equal-area circular piles, and its bearing characteristics have abnormal effect. Currently, most studies are focused on the macro aspects which demonstrate that the abnormal pile with inverted arch surface has its own superiorities in the bearing capacity and settlement controlling when compared with circular pile. However, the mobilized mechanism of abnormal effect is not fully understood. Therefore, the abnormal effect has been the scientific and technical issue to be solved firstly for establishing the analytical theory of abnormal piles with inverted arch surface. According to the usual and transparent soil model tests, through the way of combining the numerical simulation and theoretical analysis, taking the Y-section pile as the research carrier, considering the three dimensional stress state, and based on soil arching and cavity expansion theories, the methods with abnormal effect taken into account are established for the analysis of the skin friction, ultimate pile base resistance and settlement of Y-section pile. These methods for Y-section pile are expanded and applied to other abnormal piles with inverted arch surface, such as X-section and H-section piles etc., which can reveal the differences in abnormity effect and bearing mechanism between abnormal pile and traditional circular pile. This project is of great theoretical and practical significance for the unsolved scientific and technical issues of abnormal piles with inverted arch surface.

反拱曲面异形桩改变了桩"非圆即方"的传统理念，桩周具有向里凹的反拱曲面，以Y、X形桩应用最为广泛，已在浙江、江苏公路软基处理中较大规模应用，并被列入国家及地方相关规范；其经济性及承载力明显优于等面积圆形桩的特点已被工程实践所证明，同时表明其承载特性具有异形效应。目前对其研究多侧重于证明承载力和沉降与圆形桩相比具有优越性的宏观方面，其异形效应发挥机理尚未明确，异形效应已成为建立其分析理论首先要解决的科学技术问题。本项目通过常规及透明土模型试验、数值模拟和理论分析相结合的手段，以Y形桩为载体，考虑桩周土体的三向应力状态，基于土拱效应和小孔扩张理论，建立考虑异形效应的Y形桩桩侧摩阻力、桩端极限承载力及沉降分析理论，并将其拓展用于X形桩、H形桩等反拱曲面异形桩研究，揭示反拱曲面异形桩区别于传统圆形桩的的异形效应及受力机理。本项目针对反拱曲面异形桩亟待解决的科学技术问题，具有较大的理论及现实意义。