软弱松散地层盾构隧道端头土体稳定性的细观机理研究

In the soft and loose grounds, the tunnel end soil is prone to instability and failure with water gushing and burst while shield launching and arrival. It is a high risk stage in the shield tunnel construction. Before the shield launches or arrives, it is vital to implement effective and economical reinforcement on the soil of the tunnel ends. It is a key engineering problem to ensure the safety of shield tunnel construction and to save project time and costs. Among them, thorough analysis of the failure mechanism of end's soil, research on the end strength and stability of the soil mass are the key scientific issues. In this project, the end soil of shield tunnel in the typical soft clay layer and sand layer are taken as the investigated object, reducing the risks of the project and ensuring the stability of the end soil are regarded as the research goal. During the process similarity model tests and theoretical analysis method combining particle discrete element numerical calculation are used to study the soil's stability of the tunnel end from meso-scale aspects. Firstly, the meso laws and meso characteristics of progressive deformation and failure of the end soil are analyzed. Then the shaping of shear zone and the failure mechanism of the end soil are revealed. Meanwhile seepage failure mechanism of the end soil is explored in the coupling effects of seepage field and stress field. Therefrom seepage failure mode and seepage failure criterion of the end soil are deduced. Secondly, the failure forms of the end soil are analyzed, from among the characteristics and rules for the whole sliding type and partial collapse of the end soil are find out. Thirdly, the method of the soil stability judgment is deduced theoretically and then the longitudinal deformation range and transverse deformation range of the end soil are defined. Finnally, the above will provide Theoretical basis and scientific method for engineering design and construction of the soil reinforcement.

在软弱松散地层中，盾构进出洞时端头土体极易发生失稳坍塌和涌水，是盾构隧道施工中的高风险环节。深入分析端头土体的失稳破坏机理，研究端头土体的强度和稳定性，对端头土体实施有效而经济的工程加固，己成为保障盾构隧道施工安全、节约工期造价的关键科研和工程难题。本项目以典型软粘土和砂土地层盾构隧道端头土体为研究对象，以降低工程风险、保证端头土体的稳定性为研究目标，采用相似模型试验、颗粒离散元数值计算和理论分析相结合的手段，从细观角度分析端头土体渐进性变形、破坏的规律及特征，揭示端头土体的剪切带形成过程及失稳机理；探究端头土体在渗流场及应力场耦合作用下的渗透破坏机制，分析端头土体的渗透破坏形态及渗透失稳准则；研究端头土体失稳破坏形态，摸清其整体滑动失稳和局部坍塌失稳的特征和规律，得到端头土体的稳定性判断方法，从而明确端头土体的纵向和横向变形破坏范围，为端头土体的工程加固设计及施工提供理论依据和科学方法。

盾构在软弱松散地层进出洞时,端头土体极易发生失稳坍塌和涌水，是盾构隧道施工中的高风险环节。项目运用理论分析、数值模拟和模型试验等技术手段分析了端头土体的失稳破坏机理，研究了端头土体的强度和稳定性，主要有：.（1）对典型软粘土和砂性土进行了室内三轴试验和颗粒流模拟试验，确定了典型软粘土和砂性土的宏、细观力学参数、二者之间的关系及其影响因素，为盾构隧道端头土体的颗粒离散元模拟和相似模型试验提供依据。.（2）研究了典型软粘土和砂性土地层盾构隧道端头土体变形、破坏剪切带的形成机理及表观特征，土体渐进性破坏过程中土体细观特征与开挖面、地表变形特征，并分析了土体宏观参数、土颗粒细观参数、隧道埋深、隧道直径等的影响。以此为基础对端头土体的失稳破坏模式即整体滑动失稳和局部坍塌失稳分布规律及特征、端头土体稳定系数及影响因素进行了研究。.（3）建立了PFC - CFD耦合的渗透破坏颗粒流模型，分析盾构隧道端头土体砂性地层的渗透破坏过程以及渗透破坏对端头土体稳定性的影响。渗透破坏过程中流体压力场、速度场、土体应力场、孔隙率及渗透系数处于不断变化中，对端头土体稳定性具有不同程度的影响。.（4）建立了端头土体的极限平衡分析模型，并对弹性薄板模型进行了修正，并用于计算端头土体的加固厚度。丰富和发展了应用塑性松动圈理论计算横断面加固宽度的方法。得到非轴对称情况下的塑性边界方程，用于计算不同侧压力系数下的塑性边界，从而确定端头土体的横断面加固宽度。.（5）运用理论分析模型和结论，对某地铁盾构隧道端头土体的失稳破坏规律、土体稳定性及加固范围进行了分析与计算，为端头土体的工程加固设计及施工提供了理论依据和科学方法，对工程建设和施工风险防控起到了较好的指导作用。