邻近基坑开挖对地铁隧道变形的影响研究

发布时间：2018-10-23 12:35

【摘要】：地铁为城市交通命脉,紧邻地铁的基坑设计中必须考虑到对地铁区间隧道的影响。目前已有较大量研究成果阐述了基坑开挖卸荷的环境效应。但在周边存在地铁隧道的情况下,对开挖卸荷时基坑围护墙体变形的影响、受扰动土体变形规律及隧道变形响应等方面的研究相对较少,亟待解决的问题很多。本文分析和指出了邻近基坑开挖时隧道变形解析法存在的缺陷和不足,进而采用FLAC3D软件模拟武汉地铁4号线附近某基坑开挖过程,得到了在基坑开挖与隧道相互影响条件下基坑围护结构、坑底土体及隧道结构的变形规律。分别讨论了坑顶堆载、土体性质、围护结构布置、隧道与基坑水平及竖直距离对邻近隧道变形的影响。总结和提出了隧道变形控制标准和合理的加固措施及建议。主要的研究成果如下:(1)对附加应力法和附加位移法两种解析方法进行了探讨。着重对附加应力、附加位移及地基梁变形进行了求解,指出两种解析法存在的缺陷和不足:附加应力法计算复杂,无法考虑施工过程的影响,且对设有支撑时的基坑侧向卸荷应力的假设不合理;附加位移法为一种半理论半经验公式方法,受人为假设等主观因素的影响较大,且需要用前期监测数据来验证结果可靠性。(2)用FLAC3D软件模拟武汉地铁4号线附近某基坑开挖过程。基坑围护结构在坑底处位移最大,且围护墙变形受隧道的影响较大,在近隧道侧墙顶位移较大,而坑底处位移较小;在隧道离基坑长边中点较近时地铁隧道变形较大,离基坑远处较小。与三维立体模型相比,平面模型隧道最大竖向位移计算值小10%,最大水平位移计算值大10%。在坑顶堆载较大时会增大隧道的水平变形;隧道所处土层材料性质在适当范围内变化时,对隧道竖向变形影响较小,而对其水平变形影响较大。(3)总结和提出的隧道变形控制标准为:竖向变形允许值不大于10mm,水平变形允许值不大于5mm,预警值为允许值的80%。基坑分段开挖和施工过程中及时施做底板,可明显减小地铁隧道变形;而在坑底底板上快速堆载及基坑被动区土体加固的控制效果较为显著。而以往采用增加基坑内支撑或提高隧道截面刚度时,其变形控制效果较差。
[Abstract]:Subway is the lifeblood of city traffic. The influence of subway tunnel must be considered in the design of foundation pit next to subway. At present, a large number of research results have expounded the environmental effects of excavation unloading. However, in the case of the surrounding subway tunnel, the deformation of the retaining wall of the foundation pit is affected by the disturbance soil deformation law and the tunnel deformation response, so there are a lot of problems to be solved. This paper analyzes and points out the defects and shortcomings of the analytical method of tunnel deformation during excavation of adjacent foundation pit, and then uses FLAC3D software to simulate the excavation process of a foundation pit near Wuhan Metro Line 4. The deformation law of foundation pit retaining structure, pit bottom soil and tunnel structure is obtained under the interaction of excavation and tunnel. The effects of pile load, soil properties, the arrangement of enclosure structure, the horizontal and vertical distance between tunnel and foundation pit on the deformation of adjacent tunnels are discussed respectively. The control standard of tunnel deformation and reasonable reinforcement measures and suggestions are summarized and put forward. The main results are as follows: (1) two analytical methods, the additional stress method and the additional displacement method, are discussed. The additional stress, the additional displacement and the deformation of the foundation beam are solved emphatically. The defects and shortcomings of the two analytical methods are pointed out: the calculation of the additional stress method is complicated, and the influence of the construction process cannot be considered. Moreover, the assumption of lateral unloading stress of foundation pit with bracing is unreasonable, and the additional displacement method is a semi-theoretical and semi-empirical formula method, which is greatly influenced by subjective factors such as artificial hypothesis, etc. And it is necessary to verify the reliability of the results with the pre-monitoring data. (2) the excavation process of a foundation pit near Wuhan Metro Line 4 is simulated by FLAC3D software. The displacement of foundation pit enclosure structure is the largest at the bottom of the pit, and the deformation of the retaining wall is greatly affected by the tunnel, the displacement near the side wall of the tunnel is larger, but the displacement at the bottom of the pit is smaller, and when the tunnel is near the midpoint of the long side of the foundation pit, the deformation of the subway tunnel is larger. The distance from the foundation pit is smaller. Compared with the three-dimensional model, the maximum vertical displacement of the plane model tunnel is 10% smaller than that of the three-dimensional model, and the maximum horizontal displacement value is 10%. The horizontal deformation of the tunnel will be increased when the top of the pit is larger, and the vertical deformation of the tunnel will be less affected by the change of the properties of the soil layer in the tunnel within an appropriate range. (3) the allowable value of vertical deformation is not greater than 10mm, the allowable value of horizontal deformation is not greater than 5mm, and the warning value is 80% of the allowable value. In the process of excavation and construction of foundation pit, the deformation of subway tunnel can be obviously reduced by using the floor plate in time, while the control effect of quick surcharge on the bottom slab and reinforcement of soil in passive zone of foundation pit is more remarkable. In the past, the deformation control effect was poor when increasing the support inside the foundation pit or increasing the cross-section stiffness of the tunnel.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U456;TU753

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