【作者】 王忠瑾；

【导师】 谢新宇； 朱向荣；

【作者基本信息】 浙江大学 ， 岩土工程， 2013， 博士

【摘要】 桩基是一种常用的基础形式,因具有高承载力、可以有效控制沉降和不均匀沉降而得到广泛使用,其沉降计算是一个非常重要的研究课题。桩基的沉降计算因涉及到桩、土、承台的相互作用和土体力学行为的非线性而十分复杂,以往的计算方法多假定桩侧摩阻力与桩端力互不影响。随着跨海大桥等大型工程的兴建和高层建筑的迅猛增多,超长桩和长短组合桩基在工程上的应用越来越多,但与之相应的理论研究远远落后于工程实践,桩基工程也面临新的研究课题。本文对竖向荷载作用下,桩基的沉降计算开展了解析与半解析研究,主要工作和创新如下：(1)提出了一种新的桩侧摩阻力与桩-土相对位移的指数函数关系,并用于描述桩端力与桩端沉降的关系。(2)考虑桩-土相对位移与桩-土接触面上力学行为的非线性,推导了均质土层中由桩端微小位移引起基桩沉降的计算公式。逐步增大桩端位移并按(1)中提出的函数关系计算桩侧土体和桩端土的刚度变化,并进一步应用于成层土中单桩的沉降计算。(3)考虑桩身竖向压缩变形,建议了超长桩在竖向荷载作用下的沉降计算方法,分析了超长桩的承载特性。通过计算分析指出,超长桩的沉降计算需考虑桩身的非线性压缩变形。考虑桩-土接触面上力学行为的非线性,计算了由位移控制的有效桩长,并对影响有效桩长的因素进行了分析。(4)基于ABAQUS有限元软件,分析不同桩长的相互作用,对比了不同桩间距和桩长差对受荷桩与非受荷桩沉降的影响。基于Wong和Poulos建议的计算不同桩长相互作用系数的修正方法,修正了桩-桩相互作用,应用Mindlin位移解计算得到长短桩桩端的相互作用,并应用于长短组合桩基的沉降计算。本文计算结果与ABAQUS计算结果吻合较好。(5)考虑桩基的承载力随时间的变化,结合已有的研究成果和实测试验资料提出了桩基承载力随时间的计算方法。(6)提出了长期荷载作用下桩基的沉降计算公式,对其中的影响参数进行分析,并应用已有的实测研究数据证明了本方法的合理性。(7)结合某实际工程,考虑桩基承载力的时间效应,应用本文建议的长短组合桩基的沉降计算方法对该工程进行计算分析。最后,对本文工作进行了总结,并建议了进一步的研究方向。更多还原

【Abstract】 Pile foundations are usually used in practice, because of its high bearing capacity and its ability to control the settlement and reduce non uniform settlement, so the research about the settlement calculation is very significant in pile foundation design. The settlement calculation about piles is very complicated due to the interactions among the piles, the caps and surrounding soils, and the nonlinear behavior of the soils. The existing methods to calculate the settlement of piles usually considered the pile shaft and the pile end, respectively. As the sea-crossing bridges and high-rise buildings increasing, the super-long piles and long-short compound piles are widely used in practice. But the corresponding researches are backward in actual project, and the researches about pile foundations are also faced with new topics. In this paper, the analytical and semi-analytical researches about piles are present. The main work and innovative achievements are as follows:1. The Boxluscal function is present to simulate the pile shaft resistance and the corresponding relative displacement. The relationship between the pile end resistance and pile end settlement is also described using the function.2. Considering the relative displacement and the nonlinear behavior between pile shaft and surrounding soils, the calculation method about pile settlement in homogeneous soils is obtained. As the pile end settlement increased, the rigidity of the surrounding soils and pile end soils varied using the Boxluscal functions, and then disseminated in layered soils.3. Considering the nonlinear deformation of pile shaft concrete, the approach to calculate the settlement of super-long piles is obtained, and the behavior of the super-long piles is analyzed. The results show that the settlement of super-long piles is mainly due to the nonlinear deformation of the pile shaft. The effective length of super-long piles is discussed considering the nonlinearity between the pile shaft and surrounding soils, and the factors that affect the effective length of super-long piles are also analyzed.4. Based on the FEM software ABAQUS, the interactions between piles with different lengths are analyzed, considering the different space between piles and the difference in pile length. Based on the methods to revise the interaction factors proposed by Wong and Poulos, the interaction factors between piles with different lengths are revised. The interaction factors between pile bases are calculated by the displacement solution obtained by Mindlin, and then used to calculate the settlement of the long-short compound piles. The results obtained by the proposed method are well consist with that from ABAQUS.5. Considering the change of pile bearing capacity with times and the existing researches, the method to calculate the pile bearing capacity changed with time is obtained.6. The settlement calculation of pile foundations with time is proposed in this thesis, and the factors that affect the calculation are analyzed. The rationality of the proposed method is validated by the present data.7. Considering the time-effect in pile bearing capacity, a practical engineering is analyzed by the proposed methods to calculate the settlements of long-short compound piles.At the last part of this thesis, the main work is summarized and the future researches are recommended.更多还原