框架逆作的超大基坑监测分析

Monitoring and Analysis of an Extremely Large Excavation with FrameTop-Down Construction Method

塘东基地基坑是一个采用框架逆作法施工超大型深基坑,周边环境保护要求较高。基于工程特点,在基坑开挖期间进行了较为系统的监测,监测内容包括围护桩的侧移,桩后土体侧移,围护桩沉降,立柱回弹以及支撑轴力。监测数据表明:框架梁支撑与临时圆环支撑的结合很好的限制了围护桩体的水平位移,而土体的流变性对基坑的位移影响很大;底板的浇筑对围护桩和立柱的竖向位移有很好的限制作用,立柱回弹具有空间效应;临时圆环支撑结构形式有利于承担外力;框架逆作法变形略大于常规逆作法,但远小于常规顺作法基坑的变形。

Tangdong project is an extremely large excavation,which was constructed successfully by frame-top-down method.The deformation control of excavation is very strict.A systematic monitoring was carried out during the whole process of excavation.The measured excavation responses included diaphragm wall deflections,wall settlements,deflection of the soil behind wall,uplifts of interior steel columns and axial forces of propping struts.Based on the analyses of field data,the following major findings were obtained： the combination of the beams and the temporary circular strut is capable of constraining lateral wall movement,and the rheology of soil has significant influence on excavation performance;the construction of base slab helps to stabilize the soil-structure system by suppressing the vertical movements of the bored piles and interior steel column,and the vertical movements of interior steel column have 3-D effects;the temporary circular strut has a unique structure type,which is fit for bearing external forces;the excavation-induced wall deflection using frame-top-down construction method is larger than that by top-down construction method,but much smaller than that by the bottom-up construction method.