邻近河道的地铁深基坑降水开挖对周边建筑物的影响分析

Analysis on Influence on Surrounding Buildings by Dewatering and Excavating of Deep Foundation of Subway Adjacent to River

由于地铁车站其周边环境十分复杂,施工难度相对较大,尤其是在邻近河道时,其地下水补给充足,深基坑的降水开挖对周边环境造成了严重影响。以成都地铁17号线凤溪站深基坑工程为例,采用Visual Modflow对场地周边地下水渗流进行分析,采用Midas-GTS/NX对深基坑降水开挖施工进行数值模拟,通过对监测数据进行规律性分析,得出结论:富水砂卵石地层中,采用坑外管井降水+坑内疏干井+坑内明排可有效降低地下水位,但是对基坑周边建筑物沉降影响显著;随着基坑开挖至第四道内支撑被架设后,建筑物沉降才开始趋于平稳,距离基坑较近的建筑物沉降变形相对较大;地表沉降随着开挖深度的增大而增大,通常在距离基坑边缘水平方向1/5开挖深度处沉降量最大,并且靠近河道一侧的沉降量明显较大;对河道采取防渗处理可以有效地减少地下水补给,降低水头,给工程降水效果带来极大的辅助作用。

Due to the complexity of the surroundings of the subway station,the construction is relatively difficult,especially when it is adjacent to the river,the groundwater supply is sufficient,and the dewatering and excavating of the deep foundation pit has a serious impact on the surroundings.Taking the deep foundation pit engineering of Fengxi Station of Chengdu Subway Line 17 as an example,Visual Modflow is used to analyze the groundwater seepage around the site,and Midas GTS/NX is used to simulate the excavating and dewatering of deep foundation pit.Through the analysis on regular of the monitoring data,it is concluded that the use of pipe well dewatering outside the pit,drainage well inside the pit and open drainage inside the pit at the same time can effectively reduce the groundwater level in stratum of water-rich and sandy cobble,but it has a significant impact on building settlement around the foundation pit.As the foundation pit is excavated until the fourth inner support is erected,the building settlements start to stabilize,and the building settlements near the foundation pit are relatively great.The subsidence increases with the increase of the excavating depth,and the maximum subsidence is usually occurred at a position where is from the edge of the foundation pit that equals the depth of 1/5 of the excavation,while the subsidence close to river is obviously greater.The anti-seepage treatment of the river can effectively reduce the groundwater recharge,reduce the water head,and bring great auxiliary effect to the dewatering engineering.