【作者】 肖宏彬；

【导师】 王永和； 王星华；

【作者基本信息】 中南大学 ， 道路与铁道工程， 2005， 博士

【摘要】 随着我国高速公路、高速铁路和大跨、高层建筑的发展,上部结构对基础的承载力要求越来越高。大直径桩不但具有很高的承载力和较小的变形,而且还具有使用灵活、计算简洁、施工方便、节省材料等优点,因而被工程上日益广泛地采用为首选的深基础型式。 由于大直径桩的荷载传递机理和变形特征与普通中、小直径桩存在着明显的差异,因此,用中、小直径桩计算理论来分析大直径桩是不合适的。正是由于大直径桩的承载力很高,因而对大直径桩的现场试验研究受到诸多限制,使得试验成果和经验资料相对较少,理论研究也就相对滞后。基于国内外关于大直径桩问题的研究现状,在综合分析的基础上,结合国家自然科学基金课题和湖南省自然科学基金课题的研究,开展了本文的研究工作。通过理论分析、模型试验、现场测试和数值模拟相结合的方法进行研究,主要取得了如下几方面的研究成果和结论: 1)基于荷载传递的双曲线模型和大直径桩的沉降变形特点,提出了大直径桩荷载-沉降关系的解析计算方法。在此基础上,提出了可以考虑桩端沉渣影响的迭代分析方法。根据以上方法得到的计算结果与试验结果进行了对比,证明上述理论具有较好的实用性和可靠性。 2)基于剪切位移法和一维固结理论,研究了考虑固结和地面超载作用下的大直径桩的荷载传递规律,首次提出了考虑地基固结的大直径桩的荷载传递分析的解析计算方法。经过与模型试验和现场测试结果对比,方法是可靠的。 3)根据大直径桩的静载试验特点,改进了桩的荷载-沉降关系预测的GM(1,1)模型,用有限的荷载试验数据预测大直径桩完整的荷载-沉降关系,为大直径桩的沉降和承载力预测提供了合理的方法。 4)应用剪切位移法原理并考虑土的非线性变形影响,提出了多层地基中的大直径桩荷载传递分析的矩阵方法;在此基础上,应用弹性-全塑性模型和三折线软化模型,对多层地基中大直径桩的荷载传递的全过程进行了研究,提出了相应的解析计算方法;同时,根据上述理论,对嵌岩大直径桩的荷载传递进行了研究,提出了相应的分析方法和理论。理论分析结果和实测结果非常吻合。更多还原

【Abstract】 Along with the construction development in speedways, express railways, long-span structures and tall buildings in China, the requirements of bearing capacity of the foundations which support the upper structures have turned out more and more strict. The large diameter piles (LDPs) not only have stronger bearing capacity with less deformation, but also have some other advantages: flexible in application, simple in computation, convenient for construction, and economical in materials consumption, etc., thus LDPs are widely used as the first priority in deep foundations.It is unsuitable to use the theory of common small-medium piles to analyze LDPs, because there are distinguished differences in the mechanism of load transfer and deformation features between them. It is because LDPs have higher bearing capacity that the load test in-situ for them is confined for many reasons, therefore the tested results and experiential information are seldom reported, thus the theoretical research on it lays behind. Based on the present domestic and international research on LDPs and the integrated analysis, this dissertation combines the above-mentioned research with the research projects supported by the National and Hunan Provincial Natural Science Fund. By means of combining the research with the theoretical analysis, the model tests, load tests in-situ and numerical simulation, the research work has been accomplished with the following achievements:1) Based on the hyperbolic model of load transfer, this dissertation proposes an analytical method to analyze the relation between load and settlement of LDPs. Furthermore, it puts forward an iterative analytical method referring to the influence of pile-end sediment. Compared with tested results, the proposed method proved its reliability.2) Based on shear-deformation method and one-dimension consolidation theory, the present dissertation makes a systematical study on the law of load transfer of LDPs with the effect of consolidation and overload, and proposes the relative calculation method for LDPs’ loadtransfer analysis for the first time, which, compared with results of model tests and load tests in-situ, proves to be reliable.3) According to the load test characteristics of LDPs, the dissertation improves GM(1, 1) model for the prediction of load-settlement relation, and provides a reasonable approach to calculate the bearing capacity and settlement of LDPs by applying limited load test data to predict the whole relation of the load-settlement of LDPs.4) Applying the principle of shear-deformation approach and with the influence of nonlinear deformation of soil considered, the dissertation puts forward a matrix method to analyze the load transfer of LDPs in layered soils. Based on this method, a study on the whole course of load transfer of LDPs in layered soils is carried out with the application of elasticity-fully-plasticity model and tri-linear softening model, and at the same time a corresponding calculating method is also proposed. According to the above theory, a study on load transfer of LDPs socketed into rock, and its corresponding analytic methods and theories are put forth in the dissertation. These studies show that the calculated results are in good agreement with the tested data.5) Through shear-friction test, deep-hole load test and Self-balance load test, the parameter of load transfer of LDPs is measured systematically. With a further study on mechanism of load transfer of LDPs, the following conclusions are found:CD In the process of load transfer, some factors have great influence on the development of pile side friction, such as the nature of pile side soil, pile-soil relative displacement, pile-soil connection conditions and pile diameter, as well as the supporting conditions of pile-end soil.?Along with the development of pile side friction and pile-end resistance, the depth effect appears in the process of load transfer. For LDPs, the critical depth of pile side friction and pile-end resistance is about 10 times of the pile diameter.(3) In the course of load transfer, pile side friction and pile-end resistance are strengthened mutually, which is important for the design and construction of engineering.(4) For LDPs, its size effect (pile shaft diameter and pile-end diameter) on the influence of pile-side friction and pile-end resistance cannot be neglected, which is the basic difference in load transfer of LDPs from ordinary piles.(5) Influence of soft underlayer on the bearing capacity of piles is great, while it is exists. Therefore, it is necessary to ensure the thickness of bearing stratum. For LDPs, the critical thickness of bearing stratum is about 10 times of the pile-end diameter.6) The relative computer programs are designed for the above proposed analytic methods for practical use. Furthermore, the finite element method (FEM) program is also designed to simulate the load transfer of LDPs. The conclusions and results from the simulation are in good agreement with the results obtained through theoretical analysis and experimental research.更多还原