武汉I级阶地某地铁深基坑支护优化及实测分析

Analysis on Optimization and Monitoring of Supporting Structure of A Deep Metro Station Pit in First Terrace of Yangtze River in Wuhan,China

武汉目前正在长江I级阶地地区大规模进行地铁建设。在地铁车站基坑回筑施工阶段,由于换撑会严重滞缓主体结构施工,许多施工单位尝试将原设计换撑方案修改为不换撑的方案以加快施工进度。以武汉地区某地铁车站基坑工程为背景,通过数值模拟和现场实测,分析地下水位变化及有无换撑条件下地连墙变形和弯矩、地表变形、支撑轴力变化规律。理论及实测分析结果表明:坑外水位的降低导致作用在地连墙上的水土压力减小;当坑外水位小于-6.3 m时,地连墙水平位移及墙后地表沉降较原设计换撑方案仅增加10%左右;地连墙弯矩和支撑轴力均满足原设计要求,优化后的换撑方案是可行的。由于施工中存在较多不确定因素,当采用无换撑方案时需密切关注坑外水位及地连墙变形的变化,以保证工程安全顺利进行。

Many Metros are building in the first terrace of the Yangtze River in Wuhan,China. During the backfill construction of Metro station pit,support replacement will delay the construction schedule of the major structure construction. In this regard,a non-support replacement scheme is proposed. In this paper,the deformation and bending moment of diaphragm wall,settlement of ground surface,and regulations of axial stress of support structures are analyzed under the conditions of underground water level variation and that support replacement and non-support keplacement. A case of a Metro station pit in Wuhan is taken as the research background. The comparison and contrast between the monitoring data and theoretical calculations shows that： 1） Water pressure on the underground diaphragm wall reduces as water level drops; 2） The horizontal displacement of diaphragm wall and ground surface settlement behind the diaphragm wall increase by 10% compared to those in the original design; 3） The bending moment of the diaphragm wall and axial stress of the support structure can meet the original design requirements, and the optimized support replacement scheme is feasible. The water level outside the pit and the deformation of the diaphragm should be focused on when non-support replacement scheme is used.