盾构隧道施工与富水砂卵石地层的相互作用机制

In sandy gravel stratum with rich water, the construction of shield tunnel will meet some problems such as large wear and low efficiency. The mode of under-balanced pressure in the cutting face is often adopted in shield driving with more attention on the exhausting as well. But this model needs more stringent management of construction. Over excavation is easy to appear in the face and leads to severe after-construction settlement or ground collapse. Because of the prominent characteristics of individual particles, ground movement always appears noncontinuity collapse. Numerical methods and tests based on continuous deformation are difficult to reveal these phenomena. Firstly, this application studies the mechanism of ground hollow formation in the cutting face with under-balanced pressure from the mesoscopic level. Then, based on model test indoor, the laws of ground hollow development and extension in transverse and longitudinal sections will be obtained. The promotion mechanism of groundwater transfusion and overload on the surface on hollow extension, as well the load and internal force of segment lining, will be obtained too. At last, the model test of shield driving in sandy gravel stratum will be carried out to study the relevance of ground settlement and driving parameters. The research results of this application can help the constructors to understand the interaction mechanism of shield driving and surroundings better in sandy gravel stratum with rich water.

在富水砂卵石地层中，由于卵石含量高、单轴抗压强度大，盾构施工将面临刀具磨耗大、掘进效率低下等问题。为了提高掘进效率，盾构掘进通常采用"以排为主、欠压掘进"的处理模式。但该模式对施工管理要求较高，在掘削面容易引起地层超挖，导致严重的工后沉降及地层坍塌。而砂卵石地层由于颗粒个体特征突出，地层移动多体现为非连续性的塌落，基于连续变形的数值方法和试验手段难以准确的揭示这种现象。本项申请首先从细观层面入手，研究"以排为主、欠压掘进"模式下掘削面地层空洞的形成机制；其次基于室内模型试验方法，获得富水砂卵石地层空洞在隧道横、纵断面上的发展延伸规律，探明地下水渗流、地表荷载作用等对地层空洞发展的促进机制，同时获得管片衬砌受荷特征及内力分布规律；最后进行盾构掘进的室内模型试验，研究地表沉降与掘进参数的相关关系。本项申请的研究成果可以帮助建设者更深刻地认识富水砂卵石地层下盾构掘进与周围环境的相互作用。

在富水砂卵石地层中进行盾构掘进，由于地层本身卵漂石含量高、地下水位高、卵石单轴抗压强度大，盾构施工将面临刀具磨耗大、出渣困难、掘进效率低下等问题。为了提高掘进效率，盾构掘进通常采用"以排为主、欠压掘进"的处理模式。但该模式对施工管理要求高，在掘削面极易引起地层超挖，导致严重的工后沉降及地层坍塌。而砂卵石地层属于典型的粗粒土地层，地层颗粒个体特征突出，掘进过程中地层移动多体现为非连续性的塌落，基于连续变形的数值方法和试验手段难以准确的揭示这种现象。本项申请首先从细观层面入手，采用颗粒流程序PFC建立二维模型对盾构掘进对砂卵石地层扰动机理进行研究。分析了盾构掘进对砂卵石地层的扰动机理，影响范围，以及滞后沉降形成的原因。在此基础上，通过建立三维模型，进一步研究"以排为主、欠压掘进"模式下掘削面地层损失的形成机制，探明了出土率，刀盘转速，顶推速度等因素对盾构掘进效率的影响；为验证数值计算的正确性，开展了盾构掘进室内模型试验和地层损失引起的滞后沉降在隧道横纵断面扩展机制的室内模型试验，分析了直接掘进，渣土改良和地层加固情况下盾构掘进对地层位移的影响以及各掘进参数对盾构施工的影响，验证了数值计算结果的正确性，同时获得了富水砂卵石地层损失在隧道横、纵断面上的形成，发展延伸规律，探明了地下水渗流、地表车辆振动等荷载作用等对地层空洞发展的促进机制；最后进行了管片受力室内模型试验和盾构掘进对环境影响的现场测试研究，获得了不同土压和水压作用下，管片衬砌受荷特征及内力分布规律，探明了地表沉降与掘削面支护压力的关系。本课题的研究成果可以帮助建设者更深刻地认识富水砂卵石地层下盾构掘进与周围环境的相互作用，对于指导盾构在富水砂卵石地层中施工及实现安全快速掘进具有重要的现时意义。