【作者】 孙林娜；

【导师】 龚晓南；

【作者基本信息】 浙江大学 ， 岩土工程， 2006， 博士

【摘要】 复合地基是指在地基处理过程中，部分土体得到增强或被置换，或在地基中设置加筋材料，加固区是由基体和增强体两个部分组成的人工地基。其本质是在荷载作用下，基体和增强体共同直接承担上部荷载。复合地基在工程中得到越来越广泛的应用，但其沉降计算方法研究还相对落后于工程实践。在处理深厚软弱地基时沉降控制显得格外重要，因此对复合地基及按沉降控制的复合地基优化设计进行研究十分必要。本文在前人研究成果的基础上结合实际情况对刚性基础下复合地基沉降及按沉降控制的优化设计进行了较系统的研究： 根据散体材料桩复合地基荷载传递及变形机理，分析了散体材料桩与桩间土之间的应力应变关系。根据散体材料桩复合地基在荷载作用下的变形形式将压缩层分为鼓胀段、非鼓胀段和下卧层三部分，并分别采用不同方法进行沉降计算，改进了散体材料桩复合地基的沉降计算方法。文中还对影响散体材料桩复合地基沉降的主要因素进行分析。 引入剪切位移法并考虑了桩长和端阻效应对复合模量的影响，对面积加权复合模量公式进行了修正，并分析了各影响因素对复合模量的影响。 柔性桩在荷载作用下存在有效桩长。文中根据桩侧摩阻力分布形式，推导了复合地基中柔性桩的有效桩长计算公式。考虑有效桩长的影响将复合地基压缩层分为三层，即桩顶至有效桩长范围、有效桩长至桩端范围和下卧层，分别计算沉降并最终求得总沉降，改进了柔性桩复合地基沉降计算方法。 刚性桩复合地基为改善受力性状常在桩顶设置褥挚层以保证桩体有一定上刺。由于刚性桩刚度较大，桩身变形很小常可忽略不计，整个复合地基沉降主要由上下刺入量和下卧层沉降组成。根据加固区桩土单元体桩与桩间土的静力平衡，推导了考虑上下刺入量的沉降计算公式。 当采用复合地基主要要求减小沉降量时，按沉降控制的复合地基优化设计显得更为重要。影响复合地基沉降的两个主要因素为桩长和置换率，结合上述对不同类型复合地基沉降计算方法的研究，将桩长和置换率作为优化参数，沉降量作为约束条件，用桩量最省作为目标函数，结合具体工程实例，对复合地基进行优化设计，以期达到更好的经济效益。更多还原

【Abstract】 Composite foundation is an artificial foundation composed of basal body and reinforced body, in which some soil is reinforced or replaced, or some reinforced materials are set in the progress of foundation treatment. The essence of composite foundation is that the superimposed loading is shared by the basal body and the reinforced body jointly and directly. Composite foundation has been widely applied in the civil engineering, but its study on settlement is relatively fall behind the engineering practice. Settlement of composite foundation is especially important when treating deep soft foundation, so it is quite necessary to study on settlement calculation and optimum design according to settlement. Based on the known research findings, research on settlement and optimum design according to settlement of composite foundation under rigid foundation has been systematically carried out in this paper.Based on the mechanism of load transfer and deformation of discrete material piles, the relationship between stress and strain of pile and soil is analyzed. Compression layer is divided into 3 different sections: expanding, un-expanding and substratum according to deformation forms, and each section is calculated by different method. By this method, the settlement calculation of discrete material piles composite foundation has been improved. And factors influencing the settlement are analyzed in this paper.Modified formula of composite modulus is deduced in which shear deformation method is introduced and the influence of pile length and tip resistance on composite modulus is considered. Then factors influencing the composite modulus are analyzed.There exists an effective length in the flexible pile under loading. The calculation formula of effective length of pile is deduced by assuming skin friction form. Considering the influence of effective length of piles, compression layer is divided into 3 different sections: top to effective length, effective length to bottom of pile and substratum. The settlement of composite foundation is the sum of these three sections. By this method, the settlement calculation of flexible piles composite foundation has been improved.In order to improve the stress distributions, it should have the upper penetration into the cushion. The deformation of pile can be ignored because of its large rigidity. So the total settlement of rigid pile composite foundation is chiefly composed of the upper and lower penetration and substratum. According to the equilibrium equation,更多还原