邻近地铁砂层基坑微变形动态控制及监测研究

Research on the Dynamic Control and Monitoring of Micro-deformation of Sand Foundation Pit Adjacent to Subway

研究目的:深厚砂层基坑开挖及降水极易造成邻近地铁位移超标,鲜见敏感高级模型数值分析及动态调整研究依托武汉某紧邻地铁的深厚砂层基坑,采用敏感环境下小应变土体硬化高级模型进行三维数值模拟,创新性地提出支撑动态调整,通过研究及监测得出土体、桥墩和桩基变形特性以及微变形控制对策研究结论:(1)结合栈桥设计加强支撑布置及刚度,可有效减小桥墩位移的40%,由8.8 mm减为5.3 mm,降至控制标准内;(2)桥墩顶相对桩基顶因转角而位移放大明显,达1.5倍,故应严控桩基变形,桩基变形在基坑底存在显著转折点;(3)桥墩最大位移处与支撑平面计算最大位移处位置相同,数值分析与实际监测基本一致;(4)应在基坑与桥墩间设嵌入隔水层的超长止水帷幕,推荐采用TRD;(5)应采取检测、抽水试验、动态监测等多重措施确保止水帷幕质量;(6)本研究成果可供富水砂层地区地铁旁类似基坑借鉴。

Research purposes:Excavation and dewatering of deep sand foundation pit are easy to cause displacement of adjacent subway exceeding the standard.There are few studies on numerical analysis using sensitive advanced model and dynamic adjustment.Based on deep sand foundation pit adjacent to subway in Wuhan,hardening soil small-strain sensitive advanced model was used to carry out three-dimensional numerical simulation and dynamic adjustment of support was put forward innovatively.Through research and monitoring,deformation properties of soil,pier and pile foundation and micro-deformation control measures were obtained.Research conclusions:(1)Combined with trestle design,strengthening support arrangement and rigidity can effectively reduce 40%of pier displacement from 8.8 mm to 5.3 mm,which meets the control standard.(2)The displacement of pier top is obviously enlarged to 1.5 times of pile top due to rotation angle.Therefore,deformation of pile foundation should be strictly controlled,which has a significant turning point at the bottom of foundation pit.(3)The maximum displacement position of pier is the same as that of support plane.Numerical analysis is basically consistent with actual monitoring results.(4)Super long waterproof curtain inserted into water resisting layer should be set between foundation pit and pier.TRD is recommended.(5)Multiple measures such as detection,pumping test and dynamic monitoring should be taken to ensure the quality of waterproof curtain.(6)The research results can be used as reference for similar foundation pits beside subway in water-rich sand area.