【作者】 裴颖洁；

【导师】 郑刚；

【作者基本信息】 天津大学 ， 岩土工程， 2007， 博士

【摘要】 桩与承台(筏板)的不同连接方式对群桩基础的承载能力、变形性状以及桩土荷载分担比有显著影响。本文对桩筏基础和桩顶预留净空桩基础进行了深入的实验及数值分析研究并考虑了桩周土体的固结对桩筏基础工作性状的影响,研究揭示了桩筏基础及预留净空桩基础的桩身轴力、桩侧摩阻力、变形和桩土荷载分担随时间的变化规律。本文所作的主要工作和研究成果如下:1.本文设计了一种群桩桩筏基础和桩顶预留净空桩筏基础的可视化模型实验:将埋置在分层铺设染色砂带土体中的群桩基础模型受竖向荷载作用下的变形过程在可视面一侧全程拍摄,并利用PostView图像分析处理软件将所拍摄的数码照片进行分析得到桩基础在观测面上桩土相互作用位移场的变化情况。同时利用电测设备对桩身进行电测,也得到桩身轴力、侧摩阻力的变化规律。2.采用ABAQUS软件建立无台单桩、带台单桩和桩顶预留净空单桩三维有限元模型,分析了竖向荷载作用下群桩基础和预留净空基础中独立基桩的工作原理。首次研究了桩顶预留净空值的改变对桩基础轴力、侧摩阻力及变形的影响,揭示了预留净空值大小与基础受力沉降机理的关系,该结论可以引入到桩顶预留净空群桩理论中,在工程实践中可通过调整预留净空值达到合理精确控制差异沉降和调控土体荷载分担量的目的。3.采用ABAQUS软件建立考虑土体固结效应的大桩距桩筏基础和桩顶预留净空群桩基础的三维实体模型,对比分析了两种群桩基础的内力和变形随时间的变化规律,重点讨论了预留净空群桩基础在降低承台差异沉降以及减少桩身轴力方面的优势,并预测了土体长期固结效应对桩身内力变形的影响。4.本文建立了简化的高层带裙房框架的高层-筏板-群桩-土体的三维流固耦合模型,通过改变裙房筏板下桩顶与筏板的连接构造方式,研究了桩顶预留净空桩在减少因不均匀荷载及筏板变刚度等因素引起的差异沉降方面的优势,为未来高层建筑结构控制差异沉降提供了一种新思路。5.在对桩顶预留净空桩基础的实验研究和理论分析基础上,针对工程实践本文提出了一种新型的预留净空桩施工方法,既发挥了预留净空的作用又能防止桩顶与筏板之间发生水平变位等问题,便于工程实践应用。更多还原

【Abstract】 The different connected manners of piles and raft (cap) have an influence on piled raft’s bearing capacity, deformation behavior and load sharing of piles and soil. Much work have been done in this paper including performing an experimental and numerical analysis on conventional piled raft and piled raft with gap between the pile top and cap, both taken into account the influence of consolidation of soil. The findings reveal that the change with time of pile internal force, shaft resistance, deformation and load sharing of the two type of piled raft. The research and findings of this paper including:1. This paper designed a kind of experiment about visual model test of piled raft. One of the four sides of model tank is plexiglass, which make it possible to observe the deformation of pile and soil when loading. High precise digital pictures were taken to analyze the deformation field of pile and soil by using PostView. At the same time, the strain and shaft resistance can be obtained by the way of electrical measurement.2. The 3D numerical model including single pile without cap, single pile with cap and single pile with gap between the pile top and cap have been built up by ABAQUS software and the operational principle of these kinds of single pile models under the vertical load had been discussed. Put emphasis upon the influence by variation about values of this gap in piled raft’s internal force and deformation. It found out the relation between the values of gap and internal force and deformation of piled raft. Also, the accurate differential settlement value and load share ratio of soil and pile can be controlled by presetting the value of this gap in the future.3. The 3D numerical models of piled raft and piled raft with gap between pile top and cap considering the soil’s consolidation had been built up under the help of ABAQUS. The rules about these two kinds of models’internal force and deformation along with time variation had been found out. The advantage of the second piled raft on reducing the differential settlement were emphasized. Simultaneously, the influence of soil’s long term consolidation upon the internal force and deformation were forecasted.4. This paper built up an 3D numerical model which had one chip tall building with annex–piled raft-soil system. By changing the connected manners of pile and cap under the annex, the advantage on controlling the differential settlement resulted from nonuniform load or variable rigidity of raft by laying out gap between the pile top and cap was brought to light, and this viewpoint and method were new.5. Other than the theory analysis and model test, this paper brought up a new kind construction method on the piled raft with gap between pile top and cap. This method can maintain the effect of gap and strengthen the connect of pile top and cap, in addition, it was very convenient for the constructors.更多还原