【作者】 徐丽娜；

【导师】 佴磊；

【作者基本信息】 吉林大学 ， 地质工程， 2014， 博士

【摘要】 随着我国工程建设事业的蓬勃发展，大直径钻孔灌注桩在各种大型的桥梁、高层建筑和高速公路中得到了较为广泛的使用，但大直径钻孔灌注桩的理论研究还相对较为缺乏，尤其在实际工程中，桩基承载力的确定往往是通过单桩静载荷试验或者自平衡测试法获得，由于考虑到工程造价、荷载箱放置位置等原因，施加的荷载往往不足以使测试桩进入破坏状态，试桩资料虽然可以满足工程需求，但影响了其研究价值。本文在吉林省交通厅项目《大桥软岩桩基承载力评价方法研究》（2011-1-11）的基础上，以仿真分析方法为基础，对大直径钻孔灌注桩的承载特性进行分析研究，本文的研究对完善大直径钻孔灌注桩的理论研究和指导实际工程具有一定的意义和价值。在对大直径桩基承载力评价方法研究的基础上，采用仿真分析方法对单桩抗压静载荷试验和自平衡试验中单桩的承载特性进行仿真模拟，对大直径桩在不同试验方法下荷载沉降曲线的特征、桩身轴力的变化等方面进行分析，并对影响大直径钻孔灌注桩的承载特性的各种因素进行了系统的研究。建立基于BP神经网络的接触面力学参数的反分析模型，对桩土接触面的力学参数进行反分析研究。基于荷载传递理论的双曲线模型，从理论上推导出自平衡试验中单桩荷载与沉降的关系，在此基础上，利用模拟分析程序对自平衡试验中“平衡点”位置进行讨论，从而为自平衡试验设计提供参考。更多还原

【Abstract】 With the development of highway, railway, large bridges and other large-scaleconstruction projects, in order to meet the requirements of large-span, high-rise, heavyloads and complex geological conditions, pile foundations become the first choice offoundation form for many buildings or structures. The design size and bearingcapacity of the pile foundations become larger, and the application of large-diameterpiles in projects has become more and more common.Comparied with small-diameter piles, large-diameter piles have some advantages,such as the high capacity, small deformation, convenience in construction etc. In themeanwhile, there are some differences, such as the load transfer mechanism,deformation characteristics, and load bearing characteristics. Due to the large bearingcapacity of large-diameter piles, there are some limitations on study of the bearingcharacteristics using field test. Especially in the actual projects, the bearing capacityof the pile is often determined by the static load test or Osterberg-cell test, andconsidering the project cost, or the location of the balance point in the Osterberg–Celltest and other reasons, the applied load is often not enough to make the test pile intodestruction state. The bearing capacity of test pile meets the requirement of the project,but the research value is reduced. So the theoretical analysis on bearing characteristicsof large-diameter piles is relatively lagging behind the engineering practices.Therefore, in this paper, the numerical simulation is using to analysis the deformationand the load bearing characteristics of large-diameter piles, the main findings andconclusions are as following:1. Study on evaluation methods of large-diameter pile bearing capacity.Systematic comparative study on the evaluation methods of the bearing capacity oflarge-diameter pile is made, including empirical parameter method, field test (PileStatic Load test, Osterberg-cell test, dynamic load test and Statnamic method),numerical simulation method and indoor model test. The advantages and limitationsof these methods in determining the pile bearing capacity of large-diameter pile areanalyzed. 2．Simulation is used to study the bearing characteristics under different test.Numerical simulation methods are used to simulate Pile Static Load test andOsterberg-Cell test to discuss the bearing behavior of large-diameter pile underdifferent test methods. Comparing with the measured data, it found that the simulationstudy of the pile bearing characteristics is a very important and useful.3. Through the simulation experiments, the influencing factors of bearingcapacity of large-diameter piles were analyzed, including the deformation modulus ofsoil around the pile, cohesion and internal friction angle of soil around the pile,deformation modulus of soil at the pile tip, pile length, pile diameter, the elasticmodulus of pile, the interface mechanics parameters between the pile and soil. In thestudy, obtaining methods of the parameters for simulation are analyzed and discussed.Through the study, it found that the bearing capacity of the large-diameter pile linearlyincreases with the pile diameter increases. In a certain range, the bearing capacity ofthe pile can be improved with the increasing of the deformation modulus of soilaround the pile, deformation modulus of soil at the pile tip, and the length of the pile.There is no signigicant effect to increase the pile elastic modulus for improving thebearing capacity of the pile. The settlement of the pile is impacted by the interfaceshear stiffness between the pile and soil. And the the bearing capacity is impacted bycohesion and internal friction angle of interface between the pile and soil.4. Back-analysis is used on the study of the mechanical parameters of interfacebetween pile and soil. Based on the simulation results, orthogonal design and BPneural network program, the displacement back-analysis model has been established,which was used to study the mechanical parameters of interface between pile and soil.5. Based on the load transfer theory of piles and the deformation characteristics ofpile in the Osterberg–Cell test, a simulation analysis program was applied to simulatethe relationship between the load and settlement in the test. The analytical methodspresented in this paper can be considered practically, since the results from thesimulation test and on-site measurement indicate that the theoretically predicted resultis consistent with the measured one.6. The simulation analysis program can be used to determine the location of the balance point in the Osterberg–Cell test. A reasonable selection of the location of thehydraulic jack-like device (O-cell) can maximize the bearing capacity of testing pilesto obtain a more accurate ultimate bearing capacity. So this study provides a referencefor the design of the Osterberg–Cell test as well as pile foundations.更多还原