冻土与桩基础相互作用研究

发布时间：2018-05-31 04:54

本文选题：层状冻土 + 切向冻胀力　；参考：《江苏大学》2017年硕士论文

【摘要】：随着经济科技的发展以及西部大开发的深入开展,很多工程项目须在冻土上进行建设。桩基础自身众多的良好特性,例如,对冻土的良好适应性及施工的方便性等,使其成为寒区建筑物的首选基础。寒区桩基础设计中的重点和难点问题是如何合理地考虑冻土与桩基础的相互作用。对此,国内外众多学者采用理论方法及试验方法对冻土与桩的相互作用问题进行了研究,得出了十分有价值的结论。本文首先着重介绍冻土与桩基础相互作用问题的相关理论与试验研究,然后介绍了冻土相关物理力学性质,分析了冻土冻胀融沉的相关机理以及有效的防治措施。本文分别从模型试验与数值计算分析两个方面对冻土与单桩的相互作用问题进行研究。本文的研究内容包括:(1)基于自行设计的正冻土-单桩模型试验装置,对单向冻结情形下,正冻土与模型单桩的相互作用进行了室内模型试验,研究了在人工冻结条件下模型单桩的受力变形特性。首先对土样进行土工试验,测定其含水率、液塑限及渗透系数等基本物理参数,然后进行本文的冻结试验。试验中对相同含水率的土体,在三种不同冻结温度,即:-5℃,-10℃及-15℃下,土体中桩周土体温度场、桩顶上拔位移和桩侧摩阻力的进行了测定。研究发现在单向冻结过程中,温度在冻土中呈阶梯状分布,上部温度低下部温度高,期间存在着温度梯度,同时土体冻结导致土体发生冻胀变形,进而导致桩基础的上拔。桩基础的上拔过程经历三个阶段,即:桩基础无明显上拔位移阶段、上拔位移快速增长阶段和逐渐稳定阶段,其中第二阶段发生的上拔位移最大。同时,桩基在上拔过程中,土体对桩基础施加摩阻力,总体规律是先增大后不变或者稍有减小,并且在整个桩长范围摩阻力大致保持平衡。(2)对各向同性层状饱和土地基的上层施加初始冻胀应变,可得饱和冻土的简化模型。基于上述简化冻土模型,根据虚拟桩法并利用各向同性层状饱和土的圆形载荷基本解,建立了层状冻土与单桩相互作用问题的第二类Fredholm积分方程。数值求解所建立的积分方程,可得冻土中单桩的桩身轴力,切向冻胀力和桩身位移等。类似地,在层状饱和土的模型上施加融沉应变,可模拟上部融化的永久冻土或者季节性冻土。利用该上部融化的永久冻土或者季节性冻土模型,以及各向同性层状饱和土的圆形载荷基本解,建立了融化冻土和单桩相互作用的第二类Fredholm积分方程。基于该积分方程,对融化冻土中桩身轴力、负摩阻力和位移进行了数值计算。数值结果表明,桩基切向冻胀力主要分布在冻深范围内并且与冻深和冻胀应变存在正相关关系,同时他们会导致桩基础发生拉伸变形。类似地,融化冻土中桩基础所受的负摩阻力与融深与融沉应变也存在正相关关系,他们会导致桩基础发生压缩变形。对数值结果的对比发现,土体冻胀效应比融沉效应对桩基础损害更为严重。
[Abstract]:With the development of economic science and technology and the development of the western development, many projects must be built on the frozen soil. Many good characteristics of the pile foundation itself, such as the good adaptability of the frozen soil and the convenience of the construction, make it the first choice of the buildings in the cold zone. The key and difficult problems in the design of the pile foundation in the cold zone How to consider the interaction between the frozen soil and the pile foundation reasonably, many scholars at home and abroad have studied the interaction between frozen soil and pile with theoretical method and test method, and draw a very valuable conclusion. Firstly, this paper focuses on the related theory and Experimental Research on the interaction of frozen soil and pile foundation. The related physical and mechanical properties of frozen soil are introduced, and the related mechanism and effective prevention measures of frozen soil frost heave and thawing are analyzed. In this paper, the interaction between frozen soil and single pile is studied from two aspects of model test and numerical calculation. The contents of this paper include: (1) the single pile model based on self designed frozen soil In the test device, the interaction between the frozen soil and the model single pile was tested under the single freezing condition, and the stress and deformation characteristics of the single pile under the artificial freezing condition were studied. The soil samples were first tested, and the basic physical parameters such as the water content, the liquid plastic limit and the permeability coefficient were measured, and the freezing of this paper was then carried out in this paper. In the test, the temperature field of soil in the soil under three different freezing temperatures, that is, -5, -10 and -15, is measured. It is found that in the process of Unidirectional Freezing, the temperature is staircase in the frozen soil, the upper temperature is low and the lower temperature is high. There is a temperature gradient, at the same time the soil freezing causes the frost heave deformation, which leads to the uplift of the pile foundation. The uplift process of the pile foundation goes through three stages, that is, the pile foundation has no obvious uplift stage, the uplift displacement rapid growth stage and the gradual stabilization stage, the second stages of the uplift displacement are maximum. At the same time, pile foundation During the uplift process, the soil body exerts frictional resistance to the pile foundation, and the general rule is first increasing and then changing or slightly decreasing, and the frictional resistance of the whole pile length is roughly balanced. (2) the initial frost heave strain is applied to the upper layer of isotropic layered saturated soil foundation, and a simplified model of full and frozen soil can be obtained. Based on the simplified frozen soil model, Based on the virtual pile method and using the basic circular load solution of the isotropic layered saturated soil, the second kind of Fredholm integral equation for the interaction of the layered frozen soil and the single pile is established. The integral equation established by the numerical solution can be used to obtain the axial force of the pile body, the tangential frost heaving force and the displacement of the pile body in the frozen soil. On the model, the thawing strain can be applied to simulate the permafrost or seasonal frozen soil in the upper thawing. Using the permafrost or seasonal frozen soil model of the upper thawing, and the basic circular load of the isotropic layered saturated soil, the second kind of Fredholm integral equations for the melting frozen soil and the single pile are established. The numerical results show that the shear stress in the pile foundation is mainly distributed in the depth of frozen depth and has a positive correlation with the frozen depth and the frost heave strain. At the same time, they will lead to the tensile deformation of the pile foundation. Similarly, the negative effect of the pile foundation in the frozen soil is negative. There is a positive correlation between the frictional resistance and the melting depth and the thawing strain. They will lead to the compression deformation of the pile foundation. The comparison of numerical results shows that the frost heave effect is more serious than the thawing effect on the pile foundation.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

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