红粘土静压管桩承载机理及挤土效应研究

发布时间：2018-03-02 00:08

本文关键词： 管桩静载试验承载机理挤土效应细观模拟　出处：《广西科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：红粘土具有特殊的性质,不同于一般的砂土和粉质粘土,而在我国某些地区红粘土地质分布非常广泛,研究红粘土地质条件下的管桩沉桩问题及其承载机理问题很有必要。本文通过室内模型试验及颗粒流数值方法,在红粘土介质(上硬下软)中做闭口管桩静载试验,探究红粘土介质中静压管桩的承载机理及群桩挤土效应。本文的主要工作和研究成果如下:(1)本文利用自主设计的可视化模型箱,对红粘土地质的静压管桩进行室内模型试验研究,分别作出不同桩径的Q-s曲线、桩身轴力分布图及桩侧摩阻力分布图。考虑不同桩径在不同土层的静载试验,对比分析不同工况下桩端阻力、桩侧摩阻力的变化规律,揭示出红粘土介质中静压管桩的承载机理。室内模型试验结果表明,当桩端位于不同红粘土土层时,桩身轴力分布规律不同、桩侧摩阻力的峰值出现在不同深度处,侧摩阻力在不同深度处发挥程度不同,群桩挤土会导致桩体上浮,从而对桩基承载力有一定的影响。(2)本文通过工程实例分析了群桩挤土效应对桩基承载力的影响。现场静载试验表明,在红粘土地质中静压大量管桩导致了桩基承载力降低40%左右,经过复压之后,其承载力得到了大幅提高。(3)本文基于室内模型试验,应用PFC2D颗粒流数值方法模拟在红粘土介质(分层介质)的管桩静载试验,建立合理的管桩颗粒流数值仿真模型,通过颗粒流方法研究管桩静载过程中各宏细观参数的变化规律,可以弥补现有量测设备的不足,揭示沉桩过程中土体的宏细观演化机理。颗粒流数值方法研究结果表明,在沉桩过程中,水平方向的位移随着离桩轴线的距离的增加而减小,其主要影响范围大约为7倍的桩径;桩端应力远大于桩侧应力,表明桩顶荷载主要由桩端来承担;沉桩过程中桩端土体孔隙率降低,密实度增大,平均接触数增大;桩侧土体孔隙率增大,密实度降低,平均接触数减低,滑动比例增大;从特征点的轨迹可以看出,群桩挤土时不同深度处的土体运动轨迹不同,某一深度以下的土体向下挤密,而此深度以上的土体会向上隆起。
[Abstract]:Red clay has special properties, which is different from sand and silty clay in general, but it is widely distributed in some areas of China. It is necessary to study the piling problem and its bearing mechanism under the red clay geological condition. In this paper, the static load test of the closed pipe pile is done in the red clay medium by the laboratory model test and the particle flow numerical method. This paper explores the bearing mechanism of static pressure pipe piles in red clay medium and the compaction effect of pile groups. The main work and research results of this paper are as follows: 1) in this paper, we use the visual model box designed by ourselves. The static pressure pipe pile in red clay geology is studied by laboratory model test. Q-s curves of different pile diameters, axial force distribution map of pile body and frictional resistance distribution map of pile side are made respectively. The static load tests of different pile diameters in different soil layers are considered. By comparing and analyzing the variation law of pile end resistance and pile side friction under different working conditions, the bearing mechanism of static pressure pipe pile in red clay medium is revealed. The results of indoor model test show that when the pile end is located in different red clay soil layer, The axial force distribution law of pile body is different, the peak value of pile side friction appears at different depth, and the side friction is different in different depth. Therefore, it has certain influence on the bearing capacity of pile foundation. (2) this paper analyzes the effect of pile compaction on the bearing capacity of pile foundation through engineering examples. In the red clay geology, the bearing capacity of pile foundation is reduced by about 40% due to a large number of pipe piles under static pressure. After recompression, the bearing capacity of pile foundation is greatly improved. PFC2D particle flow numerical simulation method is used to simulate the static load test of pipe pile in red clay medium (stratified medium). A reasonable numerical simulation model of pipe pile particle flow is established, and the variation law of macro and meso-parameters during static loading of pipe pile is studied by particle flow method. The results of particle flow numerical method show that the displacement of horizontal direction decreases with the increase of the distance from the axis of the pile in the piling process, which can make up for the deficiency of the existing measuring equipment and reveal the mechanism of the macroscopical evolution of the soil in the piling process, and the numerical results show that the horizontal displacement decreases with the increase of the distance from the axis of the pile. The main influence range is about 7 times of the diameter of the pile, the stress at the end of the pile is far greater than the stress on the side of the pile, which indicates that the load on the top of the pile is mainly borne by the end of the pile, the porosity of the soil at the end of the pile decreases, the density increases and the average contact number increases during piling. The porosity of pile side soil increases, the compactness decreases, the average contact number decreases, and the sliding ratio increases. And above this depth of soil experience upward uplift.
【学位授予单位】：广西科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU473.1

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