地下交通枢纽多级基坑组合支护结构体系设计及变形特性研究

Study on the Design and Deformation Characteristics of Multi-stage Foundation Pit in Underground Transportation Hub with Combined Support Structure System

北京地铁M3线星火站地下枢纽是高铁星火站地下综合枢纽的一个组成部分,采用明挖法施工。因枢纽基坑内部主体结构使用功能的不同需求,基坑采用三级布置形式,基坑一侧邻近既有高铁星火站,另一侧为城市道路,基坑开挖受四层地下水影响。为了解决地铁M3线星火站地下枢纽多级基坑支护结构设计遇到的困难,开展基坑组合支护结构体系研究。首先分析枢纽基坑的空间布局特点、周边环境情况及地下水赋存特征,讨论常规支护结构体系存在的问题,基于分级支护和分级止水理念,研发基坑组合支护结构体系,详细给出各级基坑支护结构体系布置、结构参数及多级基坑开挖支护步序;然后采用数值模拟方法建立多级基坑开挖支护的三维数值计算模型,分析各级基坑的坑底隆起和围护结构变形;最后结合各级基坑围护结构变形实测结果,探讨基坑组合支护结构的变形特性。数值模拟和现场实测结果表明:各级基坑的坑底隆起及围护结构变形均满足控制值要求。

The underground hub of Xinghuo Station of M3 Line of Beijing Metro is an integral part of the underground comprehensive hub of Xinghuo Station of high-speed railway,and it is constructed by open-excavation method.Due to the different requirements of the main structure function inside the foundation pit of the hub,the foundation pit adopts the three-level layout.One side of the foundation pit is adjacent to the existing high-speed railway Xinghuo station,and the other side is adjacent to the urban road,the foundation pit is affected by four layers of groundwater.In order to solve the difficulties encountered in the design of the multi-stage foundation pit support structure of the underground hub of the Xinghuo Station on the metro line M3,this paper carries out the research of the foundation pit composite support structure system.Firstly,the spatial layout characteristics,surrounding environment and groundwater occurrence characteristics of the hub foundation pit are analyzed,and the problems of the conventional support structure system are discussed.Based on the concept of graded support and graded water stop,the combined foundation pit support structure system is developed.The paper presents in detail the layout,structural parameters and step sequence of multi-stage foundation pit excavation and support structure system at all stages,then establishes the three-dimensional numerical calculation model of multi-stage foundation pit excavation and support,analyzes the pit bottom uplift and the deformation of the retaining structure,and finally discusses the deformation characteristics of the combined retaining structure of the foundation pit based on the measured results of the deformation of the retaining structure at all stages.The results of numerical simulation and on-site monitoring show that the uplift of pit bottom and the deformation of supporting structure meet the requirements of control values.