城市轨道交通基坑工程变形控制值研究

Study on Deformation Control Value for Urban Rail Transit Foundation Pit Project

[目的]设置监测项目的变形控制值,对施工安全进行控制,以确保施工期间结构自身及周边环境稳定性,是城市轨道交通工程施工非常重要的工作内容。采用明挖法时,变形控制值因所处地质条件的不同而表现出较为明显的差异,需进一步明确不同地质条件下基坑的变形控制值。[方法]以北京地铁基坑工程为研究案例,分两个区域(西部、中东部)分别收集、整理了基坑工程的监测数据。选取基坑地面沉降、围护桩顶/墙顶处沉降、围护桩顶/墙顶处水平位移、围护桩体/墙体处水平位移作为监测项目,利用统计分析方法对这四类监测项目的控制值进行深入研究,并研究了变形值与基坑设计深度H的关系,针对两个区域基坑的四类监测项目分别提出了控制建议值。[结果及结论]这四类监测项目的控制建议值为:西部区域基坑建议分别取25~40 mm和0.10%H~0.20%H、15 mm、15 mm、25~40 mm和0.10%H~0.20%H;中东部区域基坑建议分别取30~50 mm和0.15%H~0.30%H、20 mm、20 mm、30~50 mm和0.15%H~0.30%H。

[Objective]Setting deformation control values for the monitored project and controlling the construction safety is a very important task in the construction of urban rail transit engineering,aiming to ensure the stability of the structure itself and the surrounding environment during construction.When the open-cut method is adopted,the deformation control values vary significantly with different geological conditions,and further clarification is needed on the mentioned values for foundation pits under different geological conditions.[Method]In the case study of a Beijing metro foundation pit project,the monitored data of the project are collected respectively from two areas(west,middle east)and then processed.The selected monitoring items include the ground settlement of foundation pit,the settlement and the horizontal displacement of the retaining pile top and wall top,the horizontal displacement of the retaining pile body and wall.Statistical analysis method is used to conduct in-depth study on the control values of the above four types of monitoring items,and on the relationship between the deformation value and the design depth H of foundation pit.Recommended control values of the four types of monitoring items are put forward for the foundation pits in two areas respectively.[Result&Conclusion]The recommended control values of the four types of monitoring items are as follows:25~40 mm and 0.10%H~0.20%H,15 mm,25 mm,25~40 mm and 0.10%H~0.20%H for foundation pits in the western area,and 30~50 mm and 0.15%H~0.30%H,20 mm,20 mm,30~50 mm and 0.15%H~0.30%H for foundation pits in the middle east area.