考虑桩—土相对位移的桩基沉降计算及桩基时效性研究

发布时间：2019-06-10 04:34

【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。
[Abstract]:Pile foundation is a common foundation form, which is widely used because of its high bearing capacity and can effectively control settlement and uneven settlement. Its settlement calculation is a very important research topic. The settlement calculation of pile foundation is very complex because it involves the interaction between pile, soil and cap and the nonlinear behavior of soil mechanics. Most of the previous calculation methods assume that the side friction of pile does not affect the force at the end of pile. With the construction of large projects such as cross-sea bridge and the rapid increase of high-rise buildings, the application of super-long pile and long-short composite pile foundation in engineering is more and more, but the corresponding theoretical research lags far behind the engineering practice. Pile foundation engineering is also facing new research topics. In this paper, analytical and semi-analytical research on settlement calculation of pile foundation under vertical load is carried out. The main work and innovations are as follows: (1) A new exponential function relationship between pile side friction and pile-soil relative displacement is proposed. It is also used to describe the relationship between pile end force and pile end settlement. (2) considering the nonlinear relationship between the relative displacement of pile and soil and the mechanical behavior on the contact surface of pile and soil, the formula for calculating the settlement of foundation pile caused by the small displacement at the end of pile in homogeneous soil layer is derived. The displacement of pile end is increased step by step and the stiffness change of pile side soil and pile end soil is calculated according to the function relation proposed in (1), which is further applied to the settlement calculation of single pile in layered soil. (3) considering the vertical compression deformation of the pile body, the settlement calculation method of the super-long pile under vertical load is suggested, and the bearing characteristics of the super-long pile are analyzed. Through the calculation and analysis, it is pointed out that the nonlinear compression deformation of the pile body should be considered in the settlement calculation of the super-long pile. Considering the nonlinear mechanical behavior on the pile-soil contact surface, the effective pile length controlled by displacement is calculated, and the factors affecting the effective pile length are analyzed. (4) based on ABAQUS finite element software, the interaction of different pile lengths is analyzed, and the effects of different pile spacing and pile length difference on the settlement of loaded pile and unloaded pile are compared. Based on the modified method proposed by Wong and Poulos to calculate the interaction coefficients of different pile lengths, the pile-pile interaction is modified. The Mindlin displacement solution is used to calculate the interaction between long and short pile ends, and it is applied to the settlement calculation of long and short composite pile foundation. The calculated results in this paper are in good agreement with those calculated by ABAQUS. (5) considering the change of bearing capacity of pile foundation with time, combined with the existing research results and measured test data, the calculation method of bearing capacity of pile foundation with time is put forward. (6) the settlement calculation formula of pile foundation under long-term load is put forward, and the influence parameters are analyzed, and the rationality of the method is proved by using the existing measured research data. (7) combined with a practical project, considering the time effect of bearing capacity of pile foundation, the settlement calculation method of long and short composite pile foundation proposed in this paper is used to calculate and analyze the project. Finally, the work of this paper is summarized and further research direction is suggested.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1

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