富水砂层区地铁车站基坑变形过大原因分析

Analysis of Excessive Deformation of Foundation Pit of Metro Station in Rich Water Sand Layer Area

以某明挖地铁车站基坑工程为例,结合工程地质和水文地质、基坑围护结构设计和施工情况,以及基坑开挖期监控量测数据,分析总结了基坑支护结构及周边环境变形规律、变形产生原因及可采取的风险管控措施,分析认为:富水砂层地层地铁车站基坑自身及周边变形控制的主要因素包含支撑架设及时性及轴力预加、土方开挖方式、坑内疏干降水效果、坑边动静荷载等;富水砂层区基坑桩(墙)体水平位移监测,应以管顶为起算点,并将对应墙顶水平位移值代入进行修正;同时,类似地层区地铁车站基坑支护结构设计应重点考虑第一道支撑采用钢筋混凝土支撑、增加基坑围护桩(墙)体嵌固深度的必要性。

Taking an open cut metro station foundation pit project as an example,combined with engineering geology and hydrogeology,foundation pit retaining structure design and construction,as well as monitoring and measuring data of foundation pit excavation period,this paper analyses and summarizes the deformation law,causes and possible risk control measures of foundation pit supporting structure and surrounding environment.The analysis shows that the main factors controlling the deformation of subway station foundation pit in water-rich sand stratum include the timely erection of support and pre-loading of axial force,the excavation method of earthwork,the effect of drainage and dewatering in the pit,and the dynamic and static load at the pit edge.In monitoring horizontal displacement of foundation pit pile(wall)in rich water sand layer area,the pipe top should be taken as the starting point and the corresponding horizontal displacement value of wall top should be substituted for correction.The design of foundation pit supporting structure of subway station in similar strata should focus on the necessity of using reinforced concrete as the first support and increasing the embedded depth of retaining pile(wall)of foundation pit.