软土深基坑咬合桩围护结构的施工变形特性分析

发布时间：2018-02-12 06:18

本文关键词： 软土深基坑咬合桩围护结构基坑变形现场监测 FLAC数值模拟　出处：《成都理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：目前,地铁建设特别是地铁车站建设绝大多数都选择基坑开挖并结合支护体系的方法。地铁基坑深度较深,且多处于城市建筑和管线密集地带,因此对其设计、施工的安全可靠性提出更严格要求。深基坑在施工状态下风险较大,需要通过施加支护措施确保基坑施工的安全性。随着基坑技术越来越成熟,在不同地质条件下,深基坑的支护方式也随之越来越多样化。咬合桩基坑围护结构结合了地下连续墙和普通钻孔桩各自的优势,具有较强的适用价值,但国内对于咬合桩方面的研究尚且不足,需要大量的试验和工程应用对其适用性进行研究,本文通过研究软土深基坑咬合桩围护结构在施工阶段的受力及变形特性,为以后同类型的基坑工程提供参考。本文阐述了软土深基坑咬合桩围护结构的变形理论,并结合南京新庄地铁车站深基坑的现场监控数据以及对该基坑的有限元分析结果进行了如下分析:(1)对软土深基坑的受力性能和变形机理进行了理论分析,对咬合桩的受力机理和设计方法进行研究,对软土深基坑的变形影响因素进行了分析;(2)分析了新庄站基坑监测方案,并对咬合桩围护结构水平变形、支撑轴力和周边地表沉降的监测数据进行整理,得出咬合桩围护结构体系在软土地层施工阶段的变形量和变形规律与土层中淤泥质层的关系,淤泥质层较厚的区域桩体变形相对较大,围护桩处于淤泥质层的部分可能桩体变形速率大,甚至出现部分隆起。因为淤泥质软土的蠕变性,基坑封底后围护体仍然会有持续较大变形,而淤泥质层较薄或不含淤泥质层的区域围护结构变形较小,且基坑封底后变形速率快速收敛;(3)利用有限差分析软件FLAC3D对基坑开挖过程中咬合桩体的受力和变形、支撑轴力及周边地表沉降进行数值模拟分析,并将模拟所得结果与现场监测数据作对比分析得出数值模拟结果与监测数据基本相符,证明数值模拟软件研究软土基坑咬合桩围护结构的变形特性具有准确性和适用性,通过最大主应力图找到基坑围护结构安全最不利的位置,并且发现在咬合桩围护结构中,钢筋混凝土桩(荤桩)承担了大部分的抵抗土压力的作用;(4)通过数值模拟分析不同岩土体物理力学参数和设计参数对于软土深基坑咬合桩围护结构性能的影响,并且就这些参数对围护结构变形的影响程度进行了分析,结果表明土体弹性模量、内摩擦角以及素混凝土桩混凝土强度等级变化对基坑围护结构变形及周边土体沉降影响较大,粘聚力、桩长及咬合量的影响则相对较小,为该基坑设计、施工提出优化方案,为之后同类型的深基坑设计和施工提供参考意见。
[Abstract]:At present, most subway construction, especially subway station construction, choose the method of foundation pit excavation and combined with supporting system. The subway foundation pit is deep in depth, and most of it is located in urban buildings and pipeline dense ground zone, so it is designed. The safety and reliability of the construction is more strictly required. The deep foundation pit is riskier in the construction state, so it is necessary to apply supporting measures to ensure the safety of the foundation pit construction. As the foundation pit technology becomes more and more mature, under different geological conditions, The retaining methods of deep foundation pit are more and more diversified. The retaining structure of bite pile foundation pit combines the advantages of underground continuous wall and common bored pile, and has strong applicable value, but the research on bite pile in China is still insufficient. A large number of tests and engineering applications are needed to study its applicability. In this paper, the stress and deformation characteristics of the retaining structure of occluded pile in soft soil deep foundation pit during the construction stage are studied. In this paper, the deformation theory of entrainment pile retaining structure of deep foundation pit in soft soil is expounded. Combined with the field monitoring data of the deep foundation pit of Nanjing Xinzhuang subway station and the result of finite element analysis of the foundation pit, this paper makes a theoretical analysis on the mechanical behavior and deformation mechanism of the deep foundation pit in soft soil. The stress mechanism and design method of the occlusal pile are studied. The influencing factors of the deformation of the soft soil deep foundation pit are analyzed. (2) the monitoring scheme of the foundation pit of Xinzhuang station is analyzed, and the horizontal deformation of the retaining structure of the occlusal pile is analyzed. The monitoring data of supporting axial force and surrounding surface settlement are sorted out, and the relationship between the deformation amount and deformation law and the silt layer in the soil layer during the construction phase of the masonry retaining structure system of the occlusal pile is obtained. The pile deformation in the area with thicker silt layer is relatively large, and the pile deformation rate may be high or even some uplift may occur when the retaining pile is located in the silt layer, because of the creep property of the silt soft soil, After the foundation pit is sealed, there will still be large deformation of the retaining body, while the deformation of the surrounding structure in the area without silt layer is smaller than that in the silt layer. And the deformation rate of foundation pit is convergent rapidly after foundation pit sealing. The finite difference analysis software FLAC3D is used to simulate the force and deformation of the entrainment pile during excavation, the supporting axial force and the surface settlement around the foundation pit. By comparing the simulation results with the monitoring data, the numerical simulation results are in good agreement with the monitoring data, which proves that the numerical simulation software is accurate and applicable to study the deformation characteristics of the retaining structure of the entrainment pile in soft soil foundation pit. Through the maximum principal stress diagram to find out the most unfavorable position of the foundation pit enclosure structure, and found that in the occluded pile enclosure structure, Reinforced concrete pile (pile) bears most of the function of resisting earth pressure. Through numerical simulation, the influence of physical and mechanical parameters and design parameters of different rock and soil mass on the performance of retaining structure of occluded pile in deep foundation pit of soft soil is analyzed. The influence of these parameters on the deformation of retaining structure is analyzed. The results show that the elastic modulus of soil, the angle of internal friction and the change of concrete strength grade of plain concrete pile have great influence on the deformation of foundation pit retaining structure and the settlement of surrounding soil. The influence of cohesion, pile length and bite amount is relatively small. The optimization scheme for the design and construction of the foundation pit is put forward, and the reference for the design and construction of the same type of deep foundation pit is provided.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU753

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