大直径土压平衡盾构穿越深基坑稳定性分析

发布时间：2018-05-24 13:39

本文选题：盾构隧道 + 深基坑　；参考：《山东大学》2017年硕士论文

【摘要】：地铁在修建过程中不可避免的要穿越各城市的建筑密集区,车站附近往往分布着大量的住宅、办公建筑,隧道建设和基坑开挖对周边环境的影响被越来越多的被决策者及工程人员所重视。先站后隧法方案是目前已知最为节省成本、最安全可靠也是最常用的施工方法。我国将进一步加大各城市的地铁建设力度,因此盾构进站、出站的问题应得到足够的关注,这无论是在保证周边环境安全还是在节省建设成本方面都具有十分重要的意义。在车站基坑开挖以及盾构进站过程中,基坑周边地层的应力会受到基坑支护结构变形、坑底卸荷回弹、盾构掘进压力等各种因素的影响。各种因素的影响机理及程度又不尽相同,因此很难对这一过程中各结构的稳定性进行直观评价。虽然目前关于盾构掘进期间的开挖面稳定性以及盾构对周边环境的影响方面的理论比较丰富,但关于盾构进站过程的研究依然比较缺乏。本文借助长株潭城际铁路树木岭隧道工程实测数据,以正交实验设计方法结合神经网络对该区段地层参数进行反演,利用FLAC3D数值分析软件建立盾构进、出站工程模型,研究基坑开挖、隧道掘进以及盾构进、出站期间的地表隆沉变化及地应力演化规律,针对盾构进出站期间的周边土体的应力变化、位移变化以及基坑支护结构内力变化的规律及成因进行探索。为今后车站基坑支护结构的优化提供依据。本文主要结论如下:1、在施工过程中地层损失率随着开挖天数的增加不断增大并逐渐趋于稳定,因此名义地层损失率与地层损失率相差不大,名义地层损失率测取周期短,因此更具有实用价值。2、在基坑开挖过程中,坑底卸荷回弹是以地连墙+内支撑作为支护结构的基坑的周边地表变形的主要原因。随着坑内土体的挖除基坑底的卸荷回弹可以造成基坑围护结构的上升,从而带动基坑周边土体的上升。3、当掘进面推进至距基坑边缘4m范围以内时,掘进面其前方靠近基坑部分地层会形成塌落拱,土层自然形成的塌落拱拱脚一端落在隧道支护结构上,另一端则落在基坑的围护结构上。由于土拱的存在,越靠近基坑边缘的地表土层受隧道开挖的影响越小。4、盾构进站开挖会造成基坑附近土体向远离基坑方向移动。基坑内各支撑受盾构掘进压力的影响,由地连墙、基坑中上部的支撑形成一组杠杆体系,造成顶部的支撑压力减小而底部支撑的支护压力增大的现象。5、在出站过程中,靠近基坑部分向远离基坑方向移动,而距离基坑较远的土体向靠近基坑方向移动。基坑上方支撑轴力增大,下方支撑轴力减小,中部位置的支撑轴力基本保持不变。
[Abstract]:In the construction of subway, it is inevitable to pass through the built-up areas of various cities, and there are often a large number of residential and office buildings near the stations. The influence of tunnel construction and foundation pit excavation on surrounding environment has been paid more and more attention by decision makers and engineers. The first station after tunneling method is the most cost-saving, the safest and most commonly used construction method. China will further increase the construction of subway in various cities, so the problem of shield tunneling station and exit station should be paid enough attention, which is of great significance in ensuring the safety of surrounding environment and saving the construction cost. During the excavation of station foundation pit and the process of shield tunneling, the stress around the foundation pit will be affected by the deformation of foundation pit support structure, the unloading of pit bottom, the pressure of shield tunneling, and so on. The influence mechanism and degree of various factors are different, so it is difficult to evaluate the stability of each structure directly. Although there are abundant theories about the stability of excavation surface during shield tunneling and the influence of shield tunneling on the surrounding environment, the research on the process of shield tunneling is still lacking. Based on the measured data of Shuiling tunnel of Chang-Zhuzhou-Zhuzhou-Xiangtan intercity railway, this paper uses orthogonal experimental design method combined with neural network to inverse the stratum parameters of this section, and sets up the engineering model of shield tunneling and exit station by using FLAC3D numerical analysis software. This paper studies the variation of surface uplift and subsidence and the evolution of in-situ stress during excavation, tunneling and shield tunneling, aiming at the stress changes of surrounding soil during the period of shield tunneling. The change of displacement and the internal force of foundation pit support structure are discussed. It provides the basis for the optimization of the supporting structure of the station foundation pit in the future. The main conclusions of this paper are as follows: 1. In the construction process, the formation loss rate increases with the increase of excavation days and tends to be stable gradually, so the nominal formation loss rate has little difference with the formation loss rate, and the measuring period of nominal formation loss rate is short. Therefore, it has more practical value .2.In the excavation process of foundation pit, the bottom unloading springback is the main reason for the ground deformation around the foundation pit with the support inside the ground connecting wall. With the excavation of soil in the pit, the unloading rebound of the bottom of the foundation pit can cause the rise of the retaining structure of the foundation pit, thus driving the soil around the foundation pit to rise .3. when the excavation surface is pushed within 4m from the edge of the foundation pit, Collapse arch will be formed in front of excavation surface near some ground of foundation pit, one end of collapse arch foot of soil layer will fall on tunnel support structure, the other end will fall on foundation pit enclosure structure. Because of the existence of soil arch, the soil layer near the edge of foundation pit is less affected by tunnel excavation, and the excavation of shield tunneling station will cause the soil around the foundation pit to move away from the foundation pit. Each bracing in foundation pit is affected by shield tunneling pressure, and a group of leverage system is formed by the ground connecting wall and the support of the middle and upper part of the foundation pit, which results in the reduction of the supporting pressure at the top and the increase of the support pressure at the bottom. Near the foundation pit part moves away from the foundation pit, and the soil which is far away from the foundation pit moves towards the foundation pit direction. The supporting axial force increases at the top of the foundation pit, decreases at the bottom, and remains unchanged in the middle position.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U455.43;TU473.2

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