单侧边载作用下的被动桩受力特性及计算理论研究

One-side surcharge load is often found to exist around engineering piles. The piles will be subjected to the additional load due to soil displacement caused by the one-side surcharge load, and become passive piles. At present, the research of this kind of passive piles only consider the lateral or vertical additional load due to soil displacement, but the mechanical characteristics of this kind of passive piles are not fully reflected. By means of physical model test and theoretical deduction and numerical simulation analysis, this project will carry out systematic study on the effects of lateral and vertical additional load caused by soil displacement. Based on the relationship between the lateral additional load and the lateral pile-soil interaction condition, a method to calculate the lateral passive load of the passive piles in the working state will be deduced. Considering the influence of lateral and vertical additional load, the vertical load distribution of passive piles will be reasonably assessed. Combining the vertical load and the lateral passive load of piles, a calculation model of the passive piles will be established. And the calculation method of internal force and deformation for the piles will be presented under the both actions of lateral and vertical additional load. Consequently, the research results will provide theoretical basis to evaluate the passive load effects of existing piles and planned piles, and to design the similar passive piles. The results of this study also have broad application prospects in the bridge foundations, ports, and industrial buildings.

工程桩附近经常存在单侧的边载问题，单侧边载引起的地基土位移会对邻近桩产生附加荷载而形成被动桩，目前对此类被动桩的研究仅考虑土体位移在侧向或竖向的单因素附加荷载效应，而无法反映桩身的真实受力特性。本项目利用模型箱试验，结合理论分析和数值模拟方法，对单侧边载作用下土体位移引起的桩身侧向和竖向附加荷载效应进行系统分析；通过建立侧向附加荷载与侧向桩土相互作用状态的联系，得出正常工作状态下被动桩的侧向被动荷载计算方法；综合侧、竖向附加荷载对被动桩竖向荷载传递性状的影响，合理刻画桩身竖向荷载分布模型；基于桩身竖向荷载与侧向被动荷载的联合作用，建立被动桩的受力计算模型，给出侧向和竖向附加荷载共同作用下的桩身内力变形计算方法。研究成果可为边载作用下既有或拟建结构桩的被动附加荷载效应评估，以及类似被动桩的设计计算提供理论依据，在桥梁基础、港口码头、工业厂房建筑等工程中有广阔的应用前景。

工程桩附件经常遇到因堆载或开挖引起的边载问题，这种不平衡的边载极易引起土体位移而使工程桩承受附加被动荷载，考虑不当，易引发工程事故或安全隐患，然而目前国内外对此类问题的分析多依赖于工程经验的估算，缺乏实用有效的分析方法。本项目首先通过现场测试试验、数值模拟与理论分析，揭示了土体侧移作用下桩土相互作用机制，分别建立了边载作用下排桩被动受荷的拱效应分析模型和单桩被动受荷的绕流分析模型，考虑了边载荷载水平、桩周土塑性区开展等因素的影响，给出了被动桩被动荷载的确定方法；在此基础上，结合三参数地基模型，考虑地基土非线性和桩身轴力影响，构建了边载作用下被动桩受力响应计算模型，采用矩阵传递法给出了桩身受力变形计算方法。然后，针对开挖引起的不平衡荷载问题，根据多支点支护桩受力特点，基于弹性地基梁模型，考虑开挖工况下不平衡荷载影响，推导建立了多支点支护桩结构的受力变形计算模型。最后，对上述分析模型和计算方法进行了程序实现和验证，并将之应用于工程实践分析。项目研究对不平衡荷载作用下被动桩受力特性进行了系统化分析，既可为工程中普遍遇到的类似被动桩的工程设计提供理论依据，也可为工程中既有结构桩被动受荷出现病害的加固方案选取提供理论支撑和实践指导。