长江漫滩复杂地层条件下超大超深基坑降水设计

长江漫滩地区第四系松散层是一个巨厚的复杂含水体，地下水丰富，对深基坑施工影响极大。详细分析了南京梅子洲过江通道及青奥轴线地下交通系统工程中B2-J1区基坑降水工程的特征，分区分段进行降水设计，并根据各区段的地层特征，选用合适的降水井结构，利用全孔填滤料的方式对开挖面以上含水层进行疏导，取得良好的降水效果；针对坑内、外水位差大的区段设置坑外备用井，防止因围护结构缺陷造成基坑管涌，为基坑安全增加保障，并有效地控制了降水对周边环境破坏。

Design of Deep Excavation Dewatering Under Complex Geological Conditions of Yangtze River Floodplain

The Quaternary loose layer of Yangtze floodplain area is a huge thick and complex aquifer with rich groundwater, which has great influence on deep foundation pit engineering. This paper analyzes the characteristics of dewatering project for the foundation pit in Nanjing Meizizhou river-crossing tunnel project, dewatering designs were made for each segments, and proper dewatering well structure was selected based on the features of different segment, the aquifer above the excavation surface was dredged by whole hole filling filter material with good dewatering effect. Standby wells were prepared in the segments where there was big water level difference between inside and outside pit to prevent piping caused by the defect of enclosure, increase security for foundation pit and effectively protect the surrounding environment.