岸边软土区带帽刚性桩复合地基模型试验与理论研究

发布时间：2018-03-11 06:35

本文选题：带帽刚性桩　切入点：复合地基　出处：《湖南大学》2015年硕士论文　论文类型：学位论文

【摘要】：刚性桩复合地基在深厚软土地基处理中的应用日益广泛。但由于刚性桩复合地基在较大荷载作用下,桩体易产生上刺和下刺现象,影响了地基加固效果。为此,工程中引入带帽刚性桩,它不仅可减少桩的上刺现象,而且可很好地发挥桩间土的承载能力,从而大大改善了刚性桩复合地基的承载与变形特性。然而尽管带帽刚性桩在国内外的工程实践中得到了广泛的应用,但是对于桩帽的作用机理以及荷载作用下带帽刚性桩的承载机理的研究还处于初级阶段。本文在国家自然科学基金“岸边软土区双向增强复合地基工作性状及按沉降差控制智能优化设计方法(51278186)”课题的资助下,从室内模型试验以及理论分析两个方面,对带帽刚性桩复合地基加固岸边软土地基进行了较为深入的研究。在总结已有的带帽刚性桩复合地基理论的基础上,依据相似理论进行室内模型试验的设计,采用量纲分析方法推导得出带帽刚性桩复合地基室内模型试验相似准则,确定室内模型试验参数。通过对室内模型试验试验数据的分析处理,揭示了下卧倾斜硬土层带帽刚性桩在荷载作用下桩顶压力的分布呈现中间桩体较大、两侧桩体较小的试验现象,并对桩土应力比的分布情况进行了分析;通过对带帽刚性桩桩身轴力以及桩侧摩阻力分布情况的研究,得出在桩帽以下的桩体存在负摩阻力区域,并在桩长约三分之一的位置出现基本不变的等沉面。基于塑性极限理论的上限分析法,借鉴已有数值分析和室内模型试验所揭示的带帽刚性桩破坏模式,构建了其运动许可速度场,并引入统一强度理论,根据能量平衡原理,导得了能考虑中主应力影响的带帽刚性桩极限承载力上限计算公式。同时通过参数分析,得到了带帽刚性桩极限承载力随桩帽尺寸、土的粘聚力和内摩擦角的变化规律。研究发现:考虑中主应力影响的带帽刚性桩的上限解较不考虑时有较大的提高,对于带帽刚性桩承载力计算时,实际统一强度理论中反应中主应力影响的参数取0.1~0.2附近较为合理。带帽刚性桩承载力随着桩帽尺寸的增大而增大,且桩帽直径与桩径之比D/d2时,承载力增大趋势较为明显;承载力随着土体粘聚力和内摩擦角的增大而增大。通过与已有理论方法和试验结果对比分析发现,本文提出的方法不仅在理论上更严密,而且可得到更符合实际的计算结果。
[Abstract]:Rigid pile composite foundation is widely used in the treatment of deep soft soil foundation. However, the pile body is prone to the phenomenon of burr and underburr under the action of large loads, which affects the effect of foundation reinforcement. When rigid pile with cap is introduced in engineering, it can not only reduce the burr phenomenon of pile, but also bring into play the bearing capacity of soil between piles. Thus, the bearing and deformation characteristics of rigid pile composite foundation are greatly improved. However, although rigid pile with cap has been widely used in engineering practice at home and abroad, However, the research on the action mechanism of pile cap and the bearing mechanism of rigid pile with cap under load is still in the primary stage. The method of Intelligent optimal Design for settlement difference Control (512781866), supported by the project, From the two aspects of indoor model test and theoretical analysis, this paper makes a deep research on the reinforcement of soft soil foundation with cap rigid pile composite foundation on the basis of summarizing the existing theory of composite foundation with cap rigid pile. According to the similarity theory, the indoor model test is designed, and the similarity criterion of indoor model test of rigid pile composite foundation with cap is deduced by using dimensional analysis method. The parameters of indoor model test are determined. By analyzing and processing the data of indoor model test, it is revealed that the distribution of pressure on the top of the pile with cap in inclined hard soil is larger than that of the middle pile under load. Through the study of axial force of rigid pile body with cap and the distribution of frictional resistance of pile side, it is concluded that there exists negative friction region in pile body below pile cap, and the distribution of stress ratio between pile and soil is also analyzed, and the distribution of axial force of rigid pile body with cap and frictional resistance of pile side is studied. At the position of the pile length of about 1/3, the equal-settlement surface is basically unchanged. Based on the upper bound analysis method based on plastic limit theory, the failure mode of rigid pile with cap has been revealed by numerical analysis and indoor model test. According to the principle of energy balance and the unified strength theory, the upper limit formula of ultimate bearing capacity of rigid pile with cap considering the effect of medium principal stress is derived. At the same time, through parameter analysis, the limit bearing capacity of rigid pile with cap is analyzed. The variation law of ultimate bearing capacity of rigid pile with cap with pile cap size, cohesive force of soil and angle of internal friction is obtained. It is found that the upper bound solution of rigid pile with cap considering the effect of medium principal stress is greatly improved when the cap size is not taken into account. When calculating the bearing capacity of rigid pile with cap, it is reasonable that the parameter of principal stress influence in the response of practical unified strength theory is around 0.1% 0.2. The bearing capacity of rigid pile with cap increases with the increase of pile cap size, and the ratio of diameter of pile cap to diameter of pile is D / d 2. The increasing trend of bearing capacity is obvious, and the bearing capacity increases with the increase of cohesive force and internal friction angle of soil. By comparing with existing theoretical methods and experimental results, it is found that the method proposed in this paper is not only more rigorous in theory, Moreover, more practical results can be obtained.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU473.1

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