【作者】 瞿万波；

【导师】 刘新荣；

【作者基本信息】 重庆大学 ， 桥梁与隧道工程， 2009， 博士

【摘要】 随着城市化进程的快速推进和城市人口的逐渐集聚,城市地面交通日益拥挤。为有效改善城市交通体系,城市地铁伴随着21世纪中国地下工程的大发展,以其方便、快捷、环保的设计理念,高效、安全、准点的运行模式,也必将迎来发展建设的新高潮。在地下工程开挖中,施工方法不断创新,浅埋隧道暗挖施工的洞桩工法是近年来发展起来的一种新工法,它结合了浅埋暗挖法和盖挖法的技术成果,通过对小导洞、扣拱、桩等成熟技术的有机组合,形成的一种新的浅埋隧道开挖与支护方法,能有效地控制地层松软地区地下工程开挖所引起的地表沉降,减少对人口稠密、交通拥挤、地下管线复杂的城市中心区的干扰。目前,洞桩工法虽然在北京地铁建设中得到成功应用,并取得了显著的经济效益和社会效益。但关于洞桩法的研究却较多集中在施工工艺,而设计、施工的力学效应等理论方面研究涉及较少。本文结合国家自然科学基金项目“隧道与地下空间工程结构的稳定性与可靠性”,以北京地铁十号线工体北路车站实际工程为依托,在充分借鉴前人研究的基础上,通过理论分析、模型试验、数值模拟等手段,结合现场监测成果,对采用洞桩法地铁隧道的施工力学效应进行了较为全面的研究。本文的主要研究工作如下:(1)考虑桩顶拱部支护结构压力、桩后地层压力和临时横撑的共同作用,将开挖面以下的桩简化为弹性地基梁,得到隧道边桩内力计算模型,并推导边桩在多个临时支撑作用工况、最不利工况和考虑P-?效应时的内力计算公式。(2)考虑桩顶初支拱压力以及桩侧土体的影响,对边桩稳定分析计算模型进行概化,并在此基础上推导边桩支护体系的势函数,利用尖点突变模型,得到了边桩支护体系的突变失稳必要条件。研究表明,边桩抗弯刚度越大、地层力学性质越好,桩顶荷载越小,对边桩稳定越有利。(3)采用硬质塑料管为模型桩,通过改变其直径、间距、埋置深度以及桩底支承条件等影响因素,研究洞桩法边桩在初支拱荷载和地层压力共同作用下的受力变形规律以及桩侧土压力的变化规律;并将理论计算结果与试验数据进行了对比分析;得到了边桩参数对其受力变形的控制效果。(4)运用有限元法对模型试验内容进行相应的数值模拟,并与模型试验结果进行比较研究;以工体北路站为依托工程,研究洞桩法逆筑施工分部开挖的施工力学效应;针对施工的主要过程进行三维模拟,重点分析导洞掌子面间距和主体开挖台阶长度这两个重要因素对地层变形和地表沉降变化规律的影响,为掌子面间距和台阶长度的合理取值提供依据。(5)以北京地铁十号线工体北路站为原型,通过运用数值模拟方法研究地铁站交叉口初期支护结构的施工力学效应,得出交叉口初期支护结构双向扣拱施工过程中的相互影响和交叉口初支结构拱顶沉降规律,以及交叉口区辅助受力构件的应力特征。(6)采用数值模拟方法对洞桩法与CRD工法,洞桩法顺筑与逆筑不同施工方案支护结构内力以及地层位移和地表沉降规律进行对比分析,并与现场监测成果进行比较研究。(7)基于模糊理论建立了施工方案多目标优化模型,以北京地铁十号线工体北路站为例,对施工方案进行模糊优选探讨。更多还原

【Abstract】 With the rapid urbanization and urban population’s gathering, ground traffic of the city became increasingly crowd. For effective improvement of urban traffic system, A new development opportunity of subway occured due to its convenience, rapidness, friendly environment, high efficiency, safety and timeliness. The construction methods of underground structure were innovated continuously. Pile-beam-arch(PBA)tunneling method of underground excavation in shallow-burial tunnel was one of the new construction methods in recent years. It absorbed the achievement of shallow buried tunnel and top-down construction method. With the combination of small section pilot tunnel, supporting arch and pile, a new excavation and support of shallow buried tunnel-PBA tunneling method was developed. This construction method could effectively decrease the settlement deduced by underground excavation in districts with soft stratum and lessen the disturbance to urban center with high population density, heavy traffic and complex underground utilities. With the successful application of PBA in Beijing subway, remarkable economic benefits and social benefits were gained. However, current research on PBA mainly concentrated on construction process, few involved theoretical issue.This dissertation was founded by the State Natural Sciences Foundation project‘the tunnel and the underground structure stability and the reliability’. Takes the North Gongti Road station of Beijing subway line 10 as example, systematical and thorough study and evaluations were carried on the construction mechanics of the PBA tunnel. The research methods include theoretical analysis, model tests, numerical simulation and in-situ monitor data analysis as well. The main achievements include:(1) Taking the pile buried under the excavation surface as elastic foundation beam, under the combined actions of pressures of arch and the soil and braces, a internal force calculation model was achieved. Formulas to calculate internal force were derived in three cases: supported by multiple braces, the worst condition, considering P-? effect.(2) Considering the pressure of the arch and the soil, by simplifying the stability analysis mode of the pile, potential functions of the pile was derived. Using cusp catastrophe model of large deformation, the necessary destabilization condition of pile is obtained. Large flexural rigidity and excellent mechanical properties of soil and less loading make for stability of pile. (3) Taking plastic pipe as model pile, by changing the diameter, spacing, buried depth and supporting condition of pile bottom, the variation characters of soil pressure, displacement and internal force of the pile were bained. Calculations according to the tests were also conducted to compare with the results of the tests. The effects of displacement control by different parameters were also analyzed.(4) Numerical simulations according to the tests were also conducted to compare with the results of the tests. Based on North Gongti Road station of Beijing metro line 10, 2D analysis of PBA with divisional excavating was conducted. 3D analysis, mainly focused on distance between the working faces of two pilot tunnels and on the bench length of main tunnel, was also performed to simulate the excavation procedures of PBA.(5) Take North Gongti Road station of Beijing metro line 10, 3D analysis were performed to simulate the construction procedures of preliminary supporting system of tunnel intersection. The interaction behaviors and arch settlement of preliminary supporting system of tunnel intersection as well as the stress characteristics of the assistant supporting components in tunnel intersection were analyzed.(6) Using numerical simulation, the internal forces of arch and pile, the ground displacement field and the ground surface settlement of CRD tunneling method and sequential construction and reverse construction of PBA were gained and analyzed and compared with in-situ monitoring results.(7) A multiobjective fuzzy optimization model of construction scheme decision was derived and a case was conducted according to the case of the North Gongti Road station of Beijing subway line 10.更多还原