软土基坑开挖对邻近既有隧道影响研究及展望

随着城市地铁建设的飞速发展，邻近已运营地铁线路的基坑工程大量涌现。基坑开挖必然会改变土体的原始应力场和位移场，继而引起邻近既有地铁隧道附加变形和内力。为了全面了解软土基坑开挖对既有隧道影响的研究进展，从理论研究、模型试验、数值模拟和实测分析4个方面分别阐述了软土基坑邻近施工问题的研究现状。结果表明：现阶段的理论研究主要从两阶段法入手，考虑了不同的侧重研究因素和简化条件；模型试验包括离心模型试验与常重力模型试验，可作为一种辅助研究手段与其他研究方法相互验证；数值模拟分析问题全面，结果直观，已广泛应用于工程项目的设计评估；根据基坑与隧道的相对位置关系，分别对不同工程的实测数据进行整理分析，提出考虑基坑卸荷量、形状因子、隧道埋深和水平净距等多因素的三维卸荷系数，可以较好呈现基坑开挖引起邻近隧道变形的规律性特征；基坑周围土体深层位移、围护结构变形与邻近地铁隧道变形之间存在一定联动关系；同时，总结分析了风险评价与影响分区体系以及施工控制防护技术和监控手段的探索与应用实例，为现场工程安全风险控制提供了施工经验和实践依据；最后，指出现有研究中存在的不足和尚需讨论的方面，建议深入开展邻近既有隧道设施的多维度基坑开挖时空效应研究、本构模型适用性探究、结构多元化与精细化建模、基坑降水与地下水渗流影响研究；进一步推进动态施工安全风险评价与影响分区研究，发展创新控制防护技术以及建立联动共享的新型监控成套技术体系。

Research and Prospects Regarding the Effect of Foundation Pit Excavation on an Adjacent Existing Tunnel in Soft Soil

With the rapid development of construction on subway tunnels,a large number of foundation pit projects adjacent to existing metro lines have emerged.Excavation of a foundation pit would inevitably change the original stress field and displacement field of the soil body,causing additional deformation to and internal force on an adjacent existing subway tunnel.To fully understand the research progress on the impact of foundation pit excavation on existing tunnels in soft soil,the current research status of adjacent construction problems of foundation pits in soft soil is explained through four aspects:theoretical research,model testing,numerical simulation,and actual results.The results show that the theoretical research at this stage primarily begins from the two-stage method,taking into account the different emphases on research factors and simplified conditions.Model tests include centrifugal model tests and constant gravity model tests,which can be used as an auxiliary research method to verify other research methods.Numerical simulation,which has the characteristics of comprehensive analyses and intuitive results,has been widely used in the design and evaluation of engineering projects.According to the relative position relationship between the foundation pit and the tunnel,the actual measured data of various projects are sorted and analyzed.It is proposed that a three-dimensional unloading coefficient,considering the unloading volume of the foundation pit,shape factor,tunnel depth,and horizontal clearance,can better represent the regularity of the deformation of the adjacent tunnel caused by excavation of the foundation pit.There is a certain linkage relationship between the deep displacement of soil around the foundation pit,deformation of the retaining structure,and deformation of the adjacent subway tunnel.At the same time,it summarizes and analyzes the risk evaluation and impact zoning system are summarized and analyzed,and application examples of control technology and monitoring methods are explored,which can utilize construction experience and provide a practical basis for risk control of on-site engineering.The shortcomings of existing research and the areas that require further discussion are mentioned.It is suggested that in-depth research on the space-time effects of foundation pit excavation in multiple dimensions adjacent to existing tunnel facilities,the applicability of constitutive models,the diversified and refined modeling of structures,the effects of dewatering of the foundation pit,and the seepage of groundwater should be taken into account.This will lead to the promotion of research on safety risk assessment of dynamic construction and impact zoning,development of innovative control and protection technologies,and establishment of a new type of monitoring technology system that is linked and shared.