北京市轨道交通基坑工程地表变形特性

Ground deformation characteristics of foundation pit related to the urban rail transit in Beijing

根据基坑开挖深度、地层条件的不同,对北京市轨道交通80个明挖顺作法基坑工程实测结果进行统计分析,研究确定北京砂卵石和黏性土地区深基坑开挖引起的周边地表变形规律。研究表明:基坑工程周边地表最大变形的实测结果分布形态为正态分布或半整体分布,地表沉降变形值较大;最大地表沉降的平均值约为砂卵石地区0.11%H(H为开挖深度),黏性土地区0.20%H;地表变形与桩体向基坑内、外的水平位移值有一定的对应关系;地表沉降随插入比的增大而减小,黏性土地区基坑支撑系统刚度对地表沉降有明显的影响;北京地区基坑工程周边主要影响区约为0.6H或0.7H范围以内。研究成果可对未来北京及其他地区城市轨道交通基坑工程变形大小、安全性的预测和评估、指导基坑工程设计与施工和对防止基坑事故的发生等具有重要意义。

According to various excavation depth and the formation conditions, a database of 80 engineering case histories on the urban rail transit foundation pit in Beijing is analyzed, and the ground deformation due to the foundation pit excavation in Beijing sand gravel zone and clay soil zone is studied. The results show that 1） The distribution of the maximum ground displacement approximately follows a normal distribution or half normal distribution form. 2） The average value of maximum ground settlement is 0.11%H in sand gravel zone and 0.20%H in clay soil zone, where H is the excavation depth. 3） The ground deformation is related to the pile horizontal displacement on or out of the pit. 4） When the insertion ratio increases, the ground settlement decreases. The system stiffness exerts significant influence on the ground settlement in clay soil zone. 5） The main influence zone around foundation pit is 0.6H or 0.7H. The results can be used to calculate the lateral deformation of similar projects in Beijing and other areas, helping guide the related engineering design and construction.