【作者】 刘维；

【导师】 唐晓武； Stravos Savidis；

【作者基本信息】 浙江大学 ， 岩土工程， 2013， 博士

【摘要】 城市地铁建设中,由于受到复杂地质水文条件和施工综合因素影响,盾构隧道施工会造成地层变形。盾构开挖面失稳作为盾构施工造成地层变形重要原因之一被广泛关注。本文以地铁隧道土压平衡盾构施工为背景,采用上限分析法从机理上分析了饱和成层土地质条件下盾构开挖面稳定性分别得到无渗流作用和考虑渗流作用成层土中盾构开挖面稳定支护压力上限解,并与已有极限平衡解进行分析比较。主要研究内容如下：(1)基于摩尔库伦(Mohr-Coulomb)屈服准则和相关联流动法则(Associated flow rule),建立无渗流作用成层土中开挖面失稳土体三维机动场模型,通过上限分析法得到成层土体中开挖面稳定支护压力上限解。(2)采用无渗流作用成层土中开挖面支护压力上限解分别对均质地层和成层地层中开挖面稳定进行研究。均质地层中,成层土中支护压力上限解可以退化为均质土支护压力上限解(Leca解)。成层地层中,支护压力为支持穿越土层土体所需压力与支持覆土层所需压力之和,通过研究穿越土层和覆土层的土剪切强度参数(c’,φ’)变化对支护压力影响,分析了穿越土层和覆土层对盾构开挖面稳定性影响,当穿越土层剪切强度小于覆土层剪切强度情况下,开挖面稳定性主要受穿越土层强度变化影响,覆土层对开挖面稳定影响非常有限,当覆土层剪切强度小于穿越土层时,覆土层对开挖面稳定具有不可忽略的影响。(3)基于成层土中开挖面失稳土体三维机动场模型,考虑渗透力和开挖面渗流力对盾构开挖面失稳土体的作用,并将地下水渗流作用引入开挖面稳定上限分析中,得到渗流作用下成层土中开挖面支护压力上限解。(4)采用FLAC3D数值分析研究开挖面渗流力发现渗透性较大粉土或沙土成层地层中,地下水渗流在盾构掘进阶段达到稳态且开挖面渗流力和盾构轴线处静水压力比值稳定,与此同时穿越土层中地下水往开挖面渗流方向平行于盾构轴线,而覆土层中渗流方向竖直向下；利用半承压水渗流模型推导出成层土中渗流水力梯度分布公式,并计算失稳土体中渗透力。开挖面渗流力大于破坏土体中渗透力,并随着地下水位增加开挖面渗流力成为地下水渗流对开挖面稳定影响最主要因素。渗流作用下成层土中开挖面支护压力上限解中支护压力为支持破坏土体所需压力和抵抗地下水渗流压力之和,比较土体力学性质和地下水渗流对开挖面稳定影响发现,在埋深比和地下水位同时增加条件下,地下水渗流是造成开挖面失稳最主要因素。更多还原

【Abstract】 In urban underground tunneling, the complicated hydro-geological conditons and execuation conditions somehow influence shield tunneling and make it difficult to control the soil deformation. The tunnel face instability which causes the catastrophical soil deformation and failure attracts broad attations. On the background of urban underground EPB shield tunneling, the tunnel face stability in saturated layered soil is investigated by using upper bound analysis and numerical simulation. The support pressure for the face stability without seepage application and that for the face stability under groundwater seepage application have been obtained respectively. The content of the research is divied into4parts as the following,(1) On the basis of Mohr-Coulomb constitution and associated flow rule, the3D kinemetically admissible mechanism for the failure range in the layered soil is proposed. Using the upper bound theorem, the formula of the support pressure for the face stability in the layer soil is obtained.(2) The upper bound solution presents the same support pressure as the Leca upper bound solution in the study of the face stability in the homogeneous soil. In the layerd soil, support pressure resists both of the crossed layer and cover layers. The influence of crossed layer and cover layers on the face stability is investigated. As the shear strength in cover soil is bigger than that in the crossed soil, the face stability is influenced mainly by the shear strenghth variation of the crossed soil, but as the shear strength in the cover soil is smaller than that in crossed soil, the face stability is influenced by both of the cover soil and crossed soil.(3) For the saturated layered soil, the seepage applied on the kinematically admissible mechanism is introduced into upper bound analysis. Consequently, the support presseure for the face stability under the groundwater seepage application is obtained.(4) The code FLAC3D is used to study the groundwater seepage. In the layered silty or sany soil, the seepage becomes steady-state easily in each excavation period and ratio of the seepage forces on the tunnel and hydrostatic pressure at the middle of the tunnel keeps stable. Meanwhile, the seepage in the crossed layer is horiztonal toward the tunnel face while the seepage in cover layer is vertically downward. The distribution of the seepage gradients in the layers is obtained by using the semi-aquifier model. The seepage forces on the tunnel face is bigger than the seepage forces in the failed soil, and the seepage forces becomes the key factor of the face stability as the groundwater level increases.更多还原