圆砾地基中双隧道施工和运营期致灾机理及防治研究

Recently, urban subway tunnels are mainly constructed in round gravel strata in several cities of China. With the features of being filled with single medium, high seepage coefficient and rich groundwater, which is likely to induce some practical engineering problems, such as the difficulty of ejection for water plugging during construction period, large settlement and a seriously long-term settlement after tunneling. Moreover, there are minority systematic researches on the influential factors for safety of subway tunnels construction and the long-term settlement of subway after tunneling in round gravel strata. On these grounds, multiple research methods are carried out to investigate the topic in this research subject, such as field measurement laboratory experiment, centrifuge test, constitutive theory of round gravel soil and simulation. In addition, the research subject is based on the range of Nanning Metro, which mainly passed through the round gravel strata. The research subject will include the following contents: the lagged surface collapse mechanism of twin tunneling in round gravel strata and the interaction mechanism between two tunnels, the optimal construction technique of grouting based on Evolutionary Algorithms for Multi-objective Optimization, the accumulation additional displacement of round gravel strata and the deformation of tunnel segments due to subway loading, surface subsidence and the deformation distribution of the tunnel segments due to long-term groundwater pumping and recharge and the partial drainage of tunnel segments. The application of this research results is expected to accurately predict the lagging behind of settlement and long-term settlement after tunneling in round gravel strata, and to effectively assess the serviceability of tunnel segments. Furthermore, this research subject is hopefully to provide essential theoretical supports for the consideration of disaster prevention measures in the period of design, construction and operation, hence with special theoretical and practical values.

圆砾层为我国众多城市地铁主要穿越地层，其具有骨架间充填介质单一、渗透系数大、地下水系发达等特点，易造成隧道施工注浆止水困难、地层滞后沉降大和工后长期沉降严重从而威胁运营安全等工程问题。针对这些问题，相关研究极少且缺乏系统性，本项目以南宁地铁为依托，采用现场监测、室内试验、离心模型试验、数值模拟等多种研究手段，对圆砾层地基隧道施工和运营期致灾机理及防治展开系统研究。主要包括：双隧道施工地层滞后沉降机理及其对双隧道相互作用的影响；基于“进化算法的多目标优化方法”的实用注浆工法研究；运营荷载作用下圆砾动力特性及长期变形规律和圆砾地基累积附加位移及隧道管片变形规律；地下水长期抽取回灌及不同渗漏条件所致圆砾地基沉降及管片变形规律。该项目的实施可更为准确地预测圆砾地基中隧道建设地层滞后沉降和工后长期沉降，有效评估管片的工作性能，从而为圆砾地基区域地铁的设计、施工及运营中灾害防治提供理论依据和现实指导。

针对圆砾层地基中隧道建设及运营目前相关研究存在“忽略圆砾地基土拱效应及土层扰动程度”、“忽略地下水存在形式对圆砾地层的影响”和“忽略往复运营荷载的长期影响”等不足，本课题以南宁地铁为依托，针对圆砾土地基特性，分别采用三维离心模型试验、物理模型试验、数值模拟、理论分析等研究手段，系统研究了圆砾土地层中隧道建设和运营期致灾机理及防治措施研究。主要包括：饱和圆砾土的工程特性及沉降规律；圆砾层地基中隧道开挖时隧道-土体-地下水相互作用机理；圆砾层地基中地铁运营期往复荷载作用下盾构隧道长期沉降及致灾机理。该项目的实施可为更准确地预测圆砾层地基中隧道建设及运营对土体扰动的影响，进而有效评估现有地铁隧道的工作性能，并采取针对性的治理措施，从而为维护现有地铁隧道的安全与正常工作提供理论依据，并对圆砾层地基中地铁的设计、施工及运营中的灾害防治，具有重要现实指导意义。