超深基坑无主体结构盾构接收技术的应用——以广州地铁7号线大沙东站工程为例

Application of Shield Receiving in Ultra-Deep Foundation Pit Without Main Structure:A Case Study of Dashadong Station of Gungzhou Metro Line 7

针对地铁车站主体结构进度滞后导致盾构无法按期接收的难题,以广州地铁7号线大沙东站为依托,提出超深基坑无主体结构盾构接收技术。首先,将基坑开挖至设计标高处,暂停端头井主体结构施工;其次,在仅有围护结构及底板垫层的条件下,采取调整接收井支撑位置、安装地下连续墙洞门密封装置、固定接收托架等措施;最后,通过连续监测端头井处地下连续墙变形和位移,实现全过程风险监控预警,确保盾构能顺利接收、平移、吊出。现场应用表明:1)可减少钢筋用量142 t、混凝土用量644 m^(3)、石方开挖量1680 m^(3),洞门预埋钢环2个,节省工期约160 d。2)大沙东站端头井处最大变形量21.2 mm,小于规范要求的预警值24 mm;最大变形速率1.5 mm/d,小于规范要求的预警值2.4 mm/d。该技术既可以保证超深基坑盾构接收时的安全性,又能很好地解决盾构无法按时“出洞”导致工期滞后的问题,有效避免长时间停机造成“栽头”、盾尾漏气、“裹死”等风险。

The shield cannot be received results from delayed construction of metro station main structure.Therefore,a case study is conducted on the Dashadong station of Guangzhou metro line 7,and the shield receiving technology in super-deep foundation pit without main structure is proposed.First,the foundation pit is excavated to the design elevation and the construction of the main structure of the end well is suspended.Second,measures such as adjusting the support position of receiving well,installing sealing device of underground diaphragm wall tunnel door,and fixing receiving bracket are taken under the condition of only enclosure structure and floor cushion.Finally,by continuously monitoring the deformation and displacement of the underground diaphragm wall at the end well,the entire process of risk monitoring and early warning can be realized to ensure smooth shield receive,translate and lift out.Field application results show the following:(1)The steel reinforcement,concrete,stone excavation,and steel ring were reduced by 142 t,644 m^(3),1680 m^(3),and 2,respectively,and the construction period was shortened by 160 days.(2)The maximum deformation at the end well of Dashadong station is 21.2 mm,which is less than the warning value of 24 mm required in the specification.The maximum deformation rate is 1.5 mm/d,which is less than the warning value of 2.4 mm/d required in the specification.The technology recommended can ensure safe shield receiving in ultra-deep foundation pit,guarantee the construction period,avoid shield head felling,air leakage at the shield tail,and jamming caused by a long time of shutdown.