【作者】 刘杰；

【导师】 张可能；

【作者基本信息】 中南大学 ， 地质工程， 2003， 博士

【摘要】 褥垫层作用机理及复合地基中桩与桩周土的相互作用问题是复合地基理论中重要的研究内容，弄清复合地基中垫层作用机理及桩柱体与桩周土的相互作用关系，将有助于更好地分析复合地基的承载力和沉降，有助于创造新的地基处理工艺和方法，合理而有效地采用已有的复合地基形式。 本文抓住褥垫层及两类常见的复合地基—散体材料桩复合地基和柔性桩复合地基的工作特征，基于有效的理论分析和数值分析方法、现场试验和室内模型试验，系统地研究了褥垫层作用机理、散体材料桩复合地基中桩、土的相互作用、变截面散体材料桩及其复合地基承载力计算方法、柔性桩复合地基中桩与基土的线性及非线性相互作用，这对褥垫层厚度的合理设置、褥垫层材料的选择及复合地基的设计具有重大的指导意义。 对褥垫层的作用机理，是基于桩—基土—褥垫层相互作用的工作特征，并引入等沉面的概念，建立了桩与桩周土相互作用的竖向位移协调方程，总结了垫层厚度及垫层材料对复合地基工作性状的影响。为垫层厚度的合理设置及垫层材料的选择提供了理论依据。 对散体材料桩复合地基的研究，是基于弹性理论及莫尔—库仑屈服条件，且将桩土相互作用视为空间问题，探讨了桩—土的横向相互作用过程及桩周土对桩的约束和桩对桩周土的影响。得到了合理的桩土应力比和桩土竖向变形的解析算式，也推出了桩周土处于极限平衡状态时桩体所分担的荷载的解析算式。 提出了变截面散体材料桩复合地基的概念。采用变截面散体材料桩，它与等截面散体材料桩相比，一方面，相当于提高了散体材料桩上半部的 摘要横向约束能力;另一方面，提高了基础底面以下一定深度范围内散体材料桩的面积置换率，从而达到提高散体材料桩及其复合地基承载力的目的。同时，考虑桩土接触面上剪切力的影响，将变截面散体材料桩与桩周土的相互作用问题视为空间问题和简化为平面问题两种情况，分别研究了变截面散体材料桩及其复合地基承载力的计算方法。 对柔性桩复合地基，是基于位移协调条件，并结合荷载传递法与微分方程的近似解法—子域法，提出了变截面自由单桩与地基土、刚性承台下柔性单桩和变截面柔性单桩与地基土、刚性承台下柔性群桩与地基土线性及非线性相互作用的分析方法，并得到有效桩长、桩与基土的荷载分配及刚性承台下各桩桩顶荷载分配、荷载一沉降关系、荷载传递规律等有意义的结果。 对柔性基础下柔性群桩复合地基，是基于位移协调条件和力学理论，并通过选定适当的位移模式，提出了柔性基础下柔性群桩与基土相互作用的解析算法，得到了加固区压缩量计算的解析算式，为柔性基础下柔性群桩复合地基沉降计算提供了理论基础。 由于柔性桩复合地基在基础传来的荷载作用下，其真实的边界条件应该是无限远处的位移为零，常规有限元分析难以实现这一点，因此，作者提出用有限元一无限元一接触元祸合的数值分析方法来研究柔性桩复合地基的弹塑性工作性状。得到了刚性承台下各桩分担的荷载随作用于承台上荷载的增大趋于均匀等有意义的结果。更多还原

【Abstract】 It is important research content for the action mechanism of the cushion and the interaction between reinforcements and surrounding soil in composite foundations. Understanding fully the action mechanism of the cushion and the interaction relation between reinforcements and surrounding soil in composite foundations, it is help to analysis the bearing capacity and settlement of composite foundations, to create new techniques and method of ground improvement, to adopt effectively the composite foundation types.In this paper, two typical types composite foundations, the ground with granular columns and the ground with compressible piles, the action mechanism of the cushion were systematically studied by means of theoretical analyses and numerical analyses, laboratory tests, in-site tests. It possesses important guidance meaning to determine the cushion thickness and materials, to design of composite foundations.For the action mechanism of the cushion, based on the work characteristic of interaction for pile-soil-cushion, and introduced concept of the equality sinking-surface, the harmony equation of the vertical displacement for interaction between piles and surrounding soil were established. Influence of the cushion thickness and materials on properties of the composite foundations were summarized. Theoretical basis to determine the cushion thickness and materials were offered.For the composite foundation with granular columns, based on elastictheory and Mohr-Coulomb yielding criteria, process of lateral interaction between piles and surrounding soil, restriction of surrounding soil and influence of surrounding soil on piles were studied. Analytical formulae of the pile-soil vertical deformation and stress ratio were obtained. Formula exerting load on pile were derived too at ultimate equilibrium state for surrounding soil.New concept of the composite foundation with granular columns of variable cross section is presented. Comparing granular columns of variable cross section with granular columns of uniform cross section, as both lateral restricted ability and area replacement ratio of granular columns for shallow part are improved, bearing capacity for composite foundation and granular columns can be improved. At the same time, based on influence of shear force on the pile-soil interface, and interaction between granular columns with variable cross section and surrounding soil was treated as space and simplify plane problem, calculation methods of bearing capacity for composite foundation and granular columns with variable cross section are studied, respectively.For composite foundation with compressible piles, based on displacement harmony condition, and combining with load transfer method and approximate solution of differential equation, analysis methods of linear and nonlinear interaction between piles and surrounding soil were suggested. A lot of significative results, for example availability pile length, load distribution between piles and surrounding soil, load distribution among all piles under rigidity pile-cap, load-settlement relation etc, were obtained.For composite foundation with compressible piles group, based on displacement harmony condition, mechanics theory and appropriate displacement model, analytical method of interaction between piles group and surrounding soil were put forward under flexible foundation, analytical formula which calculates deformation reinforced area were obtained, Theoretical basis to calculating settlement for composite foundation with compressible piles were offered.No displacement at the infinite location is the true boundary condition for the composite foundation with compressible piles under loads, but it is difficult for the conventional finite element to satisfy exactly this boundary condition. On the contrary, the infinite element is very convenient and effective to reflect the far field effect of the soil in an infinite domain. The key to the infinite element is to determine the nodal shape functions and the assumed elemental displacements. So更多还原