悬挂式地连墙地铁深基坑地下水渗流场及其变形规律研究

Groundwater Seepage and Deformation of Diaphragm Wall Supported Excavations of a Subway Station

以南京地铁11号线绿水湾站基坑降水为背景,综合考虑基坑围护形式、工程地质和水文地质条件,利用三维渗流计算软件Visual MODFLOW,建立悬挂式地连墙地铁深基坑三维渗流模型进行数值模拟分析,研究不同地连墙嵌固深度条件下基坑内外渗流场的变化规律和因降水导致的基坑变形特征,结果表明:地连墙的嵌固深度对坑内外地下水的渗流具有明显阻隔效应,随着地连墙嵌固深度的不断增加,坑外地下水的水位有所下降,但降水幅度较小,仅仅依赖地连墙嵌固深度的增加达到延缓坑外水头下降的目的尤为不经济;增大地连墙的嵌固深度,能够有效降低坑外地下水的水位,进而减缓因水位下降造成的基坑周边土体沉降,在实际工程中可以结合周边环境、基坑的稳定性、工程造价及施工难度要求,合理确定地连墙的嵌固深度。

This paper presents a case history of three-dimensional groundwater seepage simulation by commercial software Visual MODFLOW for the Lvshuiwan Station of No.11 Line in Nanjing.The numerical groundwater seepage model of the diaphragm wall supported deep excavation considered the type of deep excavation,geological and hydrological conditions at the project site.The influence of various embedment depths of diaphragm wall into the bedrock on the groundwater seepage field inside and outside of the excavation as well as the deformation induced by the watering operation was investigated.The results indicate:The argillaceous silty sandstone bedrock embedment has an obvious groundwater retardation effect.With the increase of embedment depth,the groundwater table outside the excavated area decreases,but the height of water table decrease is relatively small.It is not cost effective of minimizing the groundwater reducing by only increase the bedrock embedment depth of the diaphragm wall.However,adequate bedrock embedment can effectively increase the time of groundwater water drop as the result of dewatering inside the excavated area,so that the ground subsidence induced by the rapid groundwater drop can be positively delayed.The required bedrock embedment depth can be determined by considering the adjacent environment,stability of the deep excavation,construction cost and other constructability.