【作者】 白永学；

【导师】 漆泰岳；

【作者基本信息】 西南交通大学 ， 岩土工程， 2012， 博士

【摘要】 近年来,为了缓解交通拥挤问题,许多大城市开始筹划和修建地铁工程。在此期间,盾构施工诱发很多地面塌陷事故。地铁线路多位于城市道路和居民区地下,因此地面塌陷事故危害性大,引起了社会广泛关注。修建成都地铁1、2号线盾构区间时,在砂卵石地层中曾引发多次地面塌陷。目前,对岩溶塌陷和采矿引发塌陷的研究文献较多,研究内容也比较深入；而针对盾构施工诱发塌陷机理研究较少,对地层塌陷机理的认识和研究尚属起步阶段,研究深度仍停留在语言表述和简图示意水平。本文以成都地铁1、2号线为背景,针对砂卵石地层特性,对盾构施工诱发的地层塌陷演变机理进行研究,并寻找能够解决地层塌陷的对策,论文主要完成了以下几方面的工作：1.通过研究成都地铁1、2号线盾构施工诱发的多起滞后地面塌陷实例,总结了砂卵石地层盾构施工诱发滞后地层塌陷机理,该机理主要包括盾构开挖面失稳、开挖面失稳引起超出土从而形成空洞、空洞向地表移动三个方面。2.为更好掌握砂卵石层力学特性,利用大型三轴剪切试验获得砂卵石层的应力-应变曲线。针对砂卵石层粘聚力低、离散性强的特点,选用颗粒离散元法作为数值计算工具,通过对大型三轴试验的数值模拟,对砂卵石层的细观参数进行了标定,通过颗粒离散元法对滞后地层塌陷机理进行相应的数值分析。3.地层塌陷根本原因是开挖面失稳造成超出土而引起的,因此本文重点对砂卵石地层盾构开挖面稳定性问题进行了研究。总结影响盾构开挖面稳定性的主要因素,建立数值计算模型,分析内摩擦角、侧压力系数、盾构直径、盾构埋深和地下水位对开挖面稳定性的影响；研究支护压力对开挖面变形、地表沉降、开挖面的最大位移和土层应力的影响；编制位移显示程序,研究随着支护压力减小盾构开挖面变形和破坏形状的规律,提出开挖面失稳由局部破坏向整体破坏转变的模式。结合成都地铁2号线砂卵石地层盾构开挖面失稳实例,分析开挖面失稳主要原因,并提出避免砂卵石地层开挖面失稳措施。4.以梯形楔形体模型为基础,对开挖面极限支护压力公式进行重新推导,在推导过程中考虑了滑动块侧面三角形和其顶部与滑动块外部土体的相互作用力。通过数值计算分析了盾构开挖面以上破坏棱柱体的形状接近于圆形,采用直径为6m的圆形挡板模拟挡板下落实验,在三维空间修正太沙基松动土压力计算公式。文中探讨了修正梯形楔形体计算模型参数选取,并对计算模型进行了验证分析。5.砂卵石地层离散性很强,盾构施工引起地层塌陷过程属于非连续介质问题,地层坍塌变形曲线存在明显的不连续特性,因此本文选用颗粒离散单元法对地层塌陷变形进行预测。提出以现场实测法确定地层损失的计算方法,探讨了土层内部空洞分布形态,研究了砂卵石地层隧道平面断面收敛模式,分析了盾构埋深、地层损失数量和地层特性等因素对地层坍塌变形的影响,并提出基于地表沉降值影响的基础上对地层损失进行分类。多因素影响下的地层坍塌变形很难用数学表达式进行求解,本文引入BP神经网络和最小二乘支持向量机(LSSVM)对地面坍塌变形进行预测分析。6.针对砂卵石地层盾构施工特点,提出预防盾构施工诱发滞后地层塌陷的施工对策,论述了盾构刀盘开口率、开口布置、开口尺寸等设计参数。分析了同步注浆的注浆量和注浆压力关系,并进一步对理论注浆量公式进行修正；对砂卵石地层气压辅助工法适宜性进行分析,提出非满舱掘进状况下土舱内土压和气压分布模式,并进一步研究该种模式下气体压力设定值和判别开挖面产生流沙的方法；对辅助施工工法中降低地下水位工法和洞口段大管棚加固方案进行论述分析,总结砂卵石地层目前针对不同超出土量所采取的施工对策。更多还原

【Abstract】 In recent years, inorder to relieve traffic congestion problem, lots of big cities began to plan and build the subway. In the meantime, shield construction caused a great deal of surface collapse accidents. The subway lines are generally builted under the road and residential areas below. Therefore the harmfulness of surface collapse accident is very serious and it has aroused widespread social concern.When shield crossed trough the sandy cobble stratum in Chengdu metro No.1and2line, ground subsidence accidents reached as high as dozens of times. At present, there were many research literatures on karst collapse and the ground collapse caused by underground mining and these contents have been very well researched. However, ground collapse mechanism induced by shield construction was rarely researched and it is still in initial stage. The research extent remained on level of language description and sketch map. Shield crossing trough the sandy cobble stratum in Chengdu metro No.l and2lines is taken as research background. For the characteristics of sandy pebble stratum, ground collapse mechanism induced by shield is researched and the corresponding countermeasures to avoid ground collapse are proposed. The main research contents are as follows:1. Through analysis on many lagged ground collapse cases induced by shield crossing trough the sandy cobble stratum in Chengdu metro No.1and2lines, Lagged ground collapse mechanism in sandy pebble stratum is summarized. It mainly comprises of face instability, formation of cavity due to over excavation under low support pressure and upward movement of cavity.2. In order to master mechanical properties of sandy pebble stratum, the large scale triaxial test was implemented to obtain differential stress-strain curve. According to the low cohesion and heavily discrete characteristics of sandy cobble soil, numerical computation is conducted by particle discrete element method. By numerical simulation of the large scale triaxial test, the micro parameters of the sandy pebble stratum in Chengdu were calibrated. Numerical analysis on lagged ground collapse mechanism is simulated by particle discrete element method.3. The fundamental reason of ground subsidence is that the losing stability of shield face causes excessive ground loss. Therefore face stability of shield tunneling in sandy cobble stratum is emphasis of the research. The major influencing factors of face stability in sandy pebble stratum are summarized. Though numerical calculation, influence of face stability is analysed by the factors such as friction angle, lateral pressure coefficient, shield diameters, buried depth and groundwater level. The paper analyzed the influence of support pressure on shield tunnel face deformation, surface settlement, max horizontal displacement and stress of soil. Though writing displacement display program, the regularities of deformation and collapse pattern of shield face are studied along with decrease of support pressure. The process of shield face from local instability to integral instability is proposed. Combining with practical shield face instability instance in Chengdu metro No.2lines, the reason of face losing stability is analyzed. Corresponding construction measures are proposed to avoid face losing stability in sandy cobble stratum.4. On the basis of trapezoid wedge model, limited supporting pressure formula of shield excavation face was re-derived. In the process of rededuction, the forces of triangular sides and top surface on sliding block with outside soil are considered. Numerical simulation show that shape of upside sliding block in shield excavation face is circular. Hence by adopting6meters in diameter baffle, Trapdoor model test was simulated. Terzaghi loosening earth pressure formula is modified in3-dimensin space. The paper discussed the selection parameter problem on modified trapezoid wedge model and according validating analysis was carried out.5. Owing to heavily discrete characteristic of sandy cobble, ground collapse deduced by shield belongs to the field of in-continuous medium promlem. Ground collapse deformation curve has obviously discontinuous feature. Thereby the paper adopts particle discrete element mothod for displacement prediction. In-situ measurement method is proposed to obtain ground loss value. The distribution form of ground cave is explored. Ground movement pattern of shield in sandy pebble stratum was discussed. Ground collapse deformation influenced by buried depth, ground loss value and stratum characteristic is analysed. On the basis of surface settlement, ground loss are made a classification. Ground collapse deformation influenced by many factors is difficult to solve with mathematics formulas. BP neural network and least squares support vector machine method are introduced to predict surface collapse deformation.6. According to the characteristics of shield construction in sandy pebble stratum, corresponding construction measures are proposed to avoid lagged ground collapses. Shield design parameters such as aperture ratio, aperture distribution and aperture size of shield cutter head are studied. Relation between grouting pressure and grouting amount of synchronous grouting is analyzed. The suitability of air pressure auxiliary method in sandy pebble stratum is discussed. The distribution pattern of earth pressure and air pressure is proposed for unfull of soil dregs in cabin. Air pressure value, discriminant method for producing drift sand phenomena is put forward. Auxiliary methods such as decreasing groundwater level and pipe shed of portal section was analyzed. For different ground loss, corresponding construction measures are proposed to guide the construction.更多还原