基坑倾斜支护桩的桩土相互作用机理及变形与稳定分析方法研究

The current large and long excavations were supported by the conventional retaining structure with strut, which has some prominent drawbacks, including material waste, high cost, long construction period, inconvenience of constructions, difficulties in strut removal, and environmental damage. Previous researches and engineering practice have proved that the inclined retaining piles are capable of the disusing the strut and can be used in large and long excavations considering the deformation control. Based on the traditional double-row piles technique, a proposed inclined double-row piles method is proposed to further enhance the excavation depth in engineering application. However, limited investigations focused on the deformation mechanism, stability mechanism, and design methodology for the inclined retaining piles. In this project, field tests, centrifuge tests, numerical modellings, and limit analysis will be carried out to study the interaction between soil and inclined retaining piles and the distribution of earth pressure under different soil condition, excavation depth, ground surcharge and the strength and stiffness of retaining structure. The deformation and stability mechanisms of the inclined retaining piles will be investigated and compared with conventional retaining piles. Furthermore, based on the deformation control, the calculation method of optimum inclined angles will be proposed. At the same time, the calculation methods of earth pressure, deformation and stability for different inclined angles of retaining piles will be established.

当前在大面积、大长度基坑工程中所常用的传统内支撑支护方法，存在着耗材多、造价高、工期长、施工不便、支撑拆除困难并产生大量固体废弃物等诸多缺点和局限。已有研究和实践表明，采用一定倾斜角度的悬臂桩可替代内支撑，在变形可控的前提下实现大面积、大长度基坑的无支撑支护；在传统双排桩支护型式的基础上，引入倾斜支护桩形成新型双排桩可进一步提高基坑开挖深度。然而，基坑倾斜支护桩的工作和破坏机理及设计理论均缺乏研究。拟采用现场工程实测、离心机试验、数值模拟和极限分析相结合的方法，研究不同土质条件、开挖深度、地面超载、支护桩强度和刚度等因素影响下基坑开挖全过程中倾斜支护桩的桩-土相互作用机理及土压力分布规律，揭示其变形机制与稳定破坏模式，并与传统竖直支护桩工作性状与破坏模式进行对比分析。进一步，基于变形控制提出支护结构最优倾斜角的确定方法，建立不同倾斜角时支护桩的土压力、变形和稳定分析计算方法。

本项目基于现场工程实测、离心机试验、数值模拟和理论分析相结合的方法，对基坑倾斜支护的桩土相互作用、工作和破坏机理及设计理论进行了深入研究。揭示了基坑柔性倾斜支护的位变与土压力耦变机理，分析了柔性支护的刚体和挠曲变形对土压力发展的影响，明确了柔性倾斜支护的非极限到极限状态土压力演化，分析了柔性倾斜支护土体位移场的改变。揭示了基坑倾斜-竖直组合支护的变形和侧摩阻力发展的联系，阐明了侧摩阻力与桩体轴力和支护结构位移的相互影响，揭示了斜直交替支护桩的三大工作机理，即：刚架效应、斜撑效应和重力效应。揭示了基坑倾斜支护桩和斜直交替支护桩稳定破坏机理，定量描述了安全系数与基坑变形间的关系，分析了不同倾角倾斜支护桩破坏模式的转变。基于弹性地基梁法,推导出了倾斜支护桩的变形计算方法，针对其可能发生的倾覆破坏与整体失稳两种破坏模式，提出了抗倾覆稳定性与整体稳定性计算方法。对比分析了多种倾斜支护结构在控制基坑变形的能力，并阐明了其支护机理，并进行了倾斜支护结构设计参数的敏感性分析和最优化设计。获得建华工程奖特等奖1项，发布天津市工程建设标准1部。为倾斜支护在软土地区大面积、大长度基坑中的广泛应用提供了理论基础。