【作者】 李晋；

【导师】 谢永利；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2006， 博士

【摘要】 黄土的工程特性和地层分布具有其自身的特点，黄土区桥梁桩基桩—土—承台共同工作的研究越来越受到工程界和学术界的关注。本论文在总结国内外研究现状的基础上，通过现场测试和离心试验研究，利用数值仿真技术，结合理论推导，对黄土区桥梁桩基桩—土—承台共同作用进行了系统分析。 1、基于Visual Fortran平台，对大型通用有限元软件Marc进行了二次开发，研编了更适用于分析桩基和岩土问题的系列用户子程序包，主要包括：模拟地基初始应力及其释放子程序、移动分布荷载子程序、参数随工况变化的非线性弹性本构关系子程序、接触面单元子程序和动态接触状态子程序等。 2、进行了黄土地区桥梁桩基现场静载试验，试验中对各级荷载下的桩顶沉降、桩身轴力、桩端反力及桩侧摩阻力进行了现场测试和分析；同时进行了现场浸水试验，对黄土湿陷区干燥状态及浸水状态单桩竖向承载特性变化情况进行了研究。揭示了地面浸水对黄土区域桥梁桩基承载力性状的影响规律：分析了桩及桩周土浸水期间的沉降变化特征。 3、建立了分析桥梁桩基单桩空间轴对称有限元模型；结合此模型提出了计算自重湿陷性黄土地区合理桩长的方法——叠加法，得出了当中性点上、下土层摩擦力分布形式相同时，应增加的桩长与摩擦力的分布形式无关，而只与极限摩擦力的大小有关的结论。运用此方法分析了自重湿陷性黄土湿陷特性对桩基承载性状的影响规律，结果表明：在极限荷载时，中性点深度与桩长有关；湿陷系数对桩剩余承载力的影响是非线性的；定量给出了中性点深度及应增加桩长的范围。基于剪切位移法并利用弹性理论，推导了自重湿陷性黄土条件下桩基沉降、轴力及中性点计算公式，并与工程实测进行了对比验证。 4、考虑桩周土体及桩—土接触的非线性，建立了分析群桩的三维空间有限元计算模型，分析了各种土体和桩体参数条件下群桩基础的承载性状及各参数对群桩效应的影响；对Vesic法进行了改进，克服了原公式不能考虑群桩桩长的缺点；通过初应力释放子程序，模拟了黄土的自重湿陷，并进一步分析了负摩阻力条件下的群桩效应。更多还原

【Abstract】 The soil engineering characteristics and soil layer’s distribution in loess foundation have special quality. More and more study on cap-pile groups-soil interaction of bridge pile in loess area has been paid attention to. In this dissertation, based on the existing theory, by the result of tests in situation , centrifugal tests and numerical simulation, the cap-pile groups-soil interaction of bridge pile in loess area has been analyzed systemically.1 、 Based on the Visual-Fortran flat, the second development of the large common finite element MARC programme is more done. The subroutines is programmed including initial and release stress subroutine, motion load subroutine, changing parameter nonlinear elasticity model subroutine, three-dimensional and two-dimensional gap element subroutine dynamic contact subroutine, and so on.2、 Field tests on bridge pile in loess ground have been carried out .The top displacement, the axial stresses, the skin resistance and the point resistance have been measured by installing various measuring gauges. The bearing capacities before and after saturation are analyzed. It is found out that effect of surface water on the property of bearing capacity of pile foundation in loess area is significant. The regularity of settlement of pile foundation and soil around is summarized.3、 The spatial axisymmetric finite element model is established. Based on the model, a superposition method is proposed to calculate proper pile length in the self-weight collapsible loess, and it is concluded that, when the distribution of skin friction at the upper and lower parts of soil is of same pattern, added pile length has no significant influence on distribution of skin friction, but it has on ultimate friction resistance. By this method, the influence of property of the self-weight collapsible loess on pile beating performance is analyzed. It is observed that: (1)when pile is under ultimate capacity, the depth of neutral point is related to pile length, and(2)the influence of collapse coefficient on rest bearing capacity of pile is nonlinear, and(3)the quantitative range of the depth of neutral point and the added pile length is given. Based on shear displacement method and elasticity theory, the formula of estimating the settlement and axial force and the depth of neutral point of pile in self-weight collapsible loess is given. A close matching between the emulation results with the actual test data assures that the model is appropriate for analysis.4、 The spatial three-dimensional finite element model is established considering更多还原