【作者】 张昭；

【导师】 周健； 王广国；

【作者基本信息】 同济大学 ， 岩土工程， 2007， 博士

【摘要】 桩基础的沉降计算问题是目前岩土工程研究的热点问题之一,特别是桩-土—台共同分但上部荷载的问题,是国内外土木工程界十分关切而又非常复杂的问题。在以沉降为控制的桩基设计理念日益为学术界及工程界所接受的背景下,明确桩土界面处的荷载传递机理以及桩端阻力随桩端刺入变形发挥的规律,合理计算桩基础的沉降,是优化沉降控制桩基设计理论中一个迫切需要解决的关键问题。本文围绕这一课题,采用宏、细观相结合的方法对砂土中单桩和群桩的沉降机理以及荷载分布特性做了系统的研究,研究内容和成果如下:(1)提出一种基于板壳理论的桩基础试验方法,通过在钢管桩内壁贴设应变片,并经过一套成熟的数值分析方法来反算钢管桩在压入、静载过程中的摩阻力、端阻力以及侧压力的变化情况,该方法在郑州某工地上应用成功。将该试验方法应用于室内细观模型试验,对不同密实度砂土中的单桩和群桩进行模型试验。试验中利用显微数码摄像可视化跟踪技术与数值图像变形量测设备采集宏细观图像数据,对沉桩及静载过程中的土体位移场、应力场等宏观表现进行了分析。(2)建立单桩和群桩的颗粒流细观分析模型,主要分析单桩在压入、静载过程中摩阻力、端阻力以及桩周土位移场的细观变化情况;对于群桩则主要从细观角度分析由于桩间距以及承台刚度的改变对群桩工作性状的影响。(3)通过室内试验和颗粒流模拟结果以及前人的研究成果,总结了砂土中单桩的沉降模式,提出了一种可以考虑砂土状态的单桩非线性传递函数,该传递函数考虑了桩周土的近场和远场效应,可以用来分析不同密实度的砂土与桩的相互作用关系,并且使用室内试验和颗粒流模拟结果对该方法进行了验证。(4)使用所建立的传递函数,建立单桩的刚度矩阵,用来对砂土中的单桩进行非线性分析,研究了砂土中单桩的沉降规律、荷载分布情况以及不同的密实度对单桩工作性状的影响,并为以后的群桩分析作准备。(5)在单桩分析的基础上建立群桩的刚度矩阵,然后建立土单元、板单元的刚度矩阵,最后形成桩—土—台整体刚度矩阵,最后由静力平衡条件求解群桩沉降及承台反力。(6)利用国内外发表的群桩试验结果和室内模型试验对所建立的群桩计算方法进行了验证,在此基础上分析了群桩的沉降机理,并比较了群桩沉降与单桩沉降的异同,最后分析了由于桩间距、桩的长径比、承台刚度等因素的改变对群桩工作性状的影响。更多还原

【Abstract】 The calculation of the pile foundation settlement problem is a hot issue of geotechnical engineering studies, especially the question of the total applied load carried by pile-soil-cap. It’s a very complex problem that has been paid attention to by internal and international civil engineers. Under the background of settlement-control composite pile design theory being widely accepted by academics and the engineering, research on the load transfer mechanism at the pile and soil interface and the development of the tip resistance with the pile tip penetration displacement, and how to calculate the settlement of pile foundation, which is the key to optimize settlement-controlled composite pile design theory. According to this subject, this paper does systematic researches on settlement mechanism and load distribution of single pile and pile groups by combinating macro and meso methods. The results are as follows:(1) Based on the plate-shell theory, a pile testing method is established. through affixing the strain gauge on the inside wall of steel tube pile, a perfect numerical analysis method to back-calculate the tip resistance, skin pressure, lateral pressure during the pile driving and static loading process is discussed. Finally it is applicated successfully in Zhengzhou. This method is also used to simulate the single pile and pile group with different density sands in lab meso-scale model test. Microscopic digitization technique for tracing and digital photography deformation measure system is introduced to collect the macro and meso images during each test. The Macro phenomenon of the soil displacement field and stress change field are analyzed during driving and static loading process.(2) The particles flow code analysis models of the single pile and pile group are established, which are introduced to analysis the meso phenomenon of the soil displacement field, friction resistance, tip resistance changing during the single pile driving and static loading process. Finally the influence of pile group behaviors when the distance of pile-pile and the stiffness of cap changing from the micros level are analysised.(3) Based on laboratory tests, particles flow code simulation results and the previous study conclusions, the settlement form of the single Pile in sands is aggregated. Then one nonlinear transfer function of the single pile which can consider the state of sands is proposed. The soil near-field and far field effects are considered in the transfer function, which can be introduced to analysis the relationship of the different density sands and piles interaction. At last the transfer function is verificated by laboratory tests.(4) Stiffness matrix of single pile is established to research the settlement law by introducing the transfer function. After the method being certificated, the load distribution of single pile, the behavior of single pile in different density sands are studied.(5) Based on the analysis of single pile, the stiffness matrixs of pile groups, soils and plate are introduced. Then, the total stiffness matrix of pile-soil-cap is established. The settlement of pile groups and contact pressure of the cap can be solved by the static equilibrium using the total stiffness matrix in the end.(6) Certificated the settlement calculation method of pile groups by laboratory tests results and the previous study conclusions, the settlement mechanism is analyzed of pile group. The different forms between the settlement of single pile and pile group are discussed. Finally the influence of pile group behaviors while the changing of the distance of pile-pile, length-diameter ratio, stiffness of the cap are analyzed.更多还原