软土地区紧邻地铁隧道深基坑支护设计与实践

以上海竹园2-16-1地块项目深基坑工程为背景,介绍了邻近地铁的软土深基坑变形控制方法及其效果。根据基坑工程的特点,设计时采取了多种地铁保护专项技术措施,包括基坑分区实施方案、支护体系、钢支撑轴力补偿系统、坑内被动区加固、承压水控制措施等。结果表明:基坑各分区地下连续墙最大侧向位移小于上海软土地区基坑地下连续墙最大侧移的统计平均值0.42%H(H为基坑最大开挖深度),特别是靠近地铁侧的地下连续墙最大侧向位移接近上海软土地区基坑地下墙最大侧移的统计下限值0.1%H; 地铁侧坑外承压水位总体保持在比较平稳的水平,最大水位变化仅为0.72 m; 邻近的地铁隧道上行线和下行线的累计最大沉降量分别为8.2 mm和5.1 mm,均小于地铁下沉量允许值(20 mm),且隧道曲率半径满足控制值要求; 本基坑采用的系统变形控制措施有效地保障了邻近地铁的安全,其设计和施工方法可以为软土地区同类基坑工程设计提供参考。

Supporting Design and Application of Deep Excavation Adjacent to Metro Tunnels in Soft Soil Area

The deformation control methods of the deep excavation adjacent to metro and its effect are introduced based on the deep excavation of Shanghai Zuyuan 2-16-1 Block project. According to the characteristics of the excavation engineering, a variety of technical measures were taken to protect the adjacent metro tunnels, including zoned excavation method, proper supporting system, steel support automatic axial force compensation system, ground treatment, and confined ground water control design. The results show that the maximum lateral displacement of diaphragm wall for each excavation zone is less than the statistical average value(0.42%H, H is the excavation depth)in Shanghai soft deposit, while the maximum lateral displacement of diaphragm wall in the excavation zones adjacent to the metro tunnels is quite close to the statistical lower limit value, which is 0.1%H. The confined water level near the metro tunnel area maintains a relatively stable level and the maximum water level variation is only 0.72 m. The cumulative maximum settlement of the adjacent metro tunnels upstream and downstream are 8.2, 5.1 mm respectively, which are less than the 20 mm allowable limit. Moreover, the tunnel curvature radius meets the requirement of the control value. Deformation control methods adopted in the project are proved to be effective in protecting the safety of the adjacent metro tunnels. Design and construction methods in the project can provide a reference for similar excavation projects in soft soil area.