上海软土地区某逆作法地铁深基坑变形

Deformation behaviors of deep top-down metro excavation in Shanghai soft clay

以上海软土地区某逆作法地铁车站深基坑项目为工程背景,通过分析现场监测数据,研究逆作法深基坑的变形性状及对周围环境的影响.研究结果发现:该基坑变形表现出显著的空间效应:中间标准段围护结构最大侧移的统计范围为(0.25%~0.45%)H,明显大于端头井的(0.10%~0.25%)H,中间标准段立柱隆起的上限为0.26%H,明显大于端头井的上限0.18%H,中间标准段开挖引起的管线沉降明显大于端头井开挖引起的管线沉降;既有地下结构对基坑变形有明显的遮拦效应,导致中间标准段西侧的围护结构侧向变形较小;基坑开挖导致邻近浅基础建筑物发生较大的沉降,甚至破坏建筑物的结构整体性,引发墙体开裂;受软土流变特性的影响,浅基础建筑物和地下管线都产生一定程度的工后沉降.

The measured deformation behaviors of the excavation and its influences on environment were analyzed based on field instrumentation data from a top-down excavation in Shanghai soft clay.Results showed that excavation behaviors exhibited apparent spatial corner effect.The maximum lateral wall deflections at the central standard segments were（0.25%~0.45%）H,greater than（0.10%~0.25%）H at end shafts.The upper bound of column uplifts was around 0.26%H at the central standard segments,greater than 0.18% Hat end shafts.The settlements of utility pipelines near the central standard segments were greater too.The existing underground structures adjacent to the west pit side imposed apparent barrier effect on excavation deformations,i.e.,relatively smaller lateral wall deflections were measured along the west pit side.Excavating induced significant settlements of adjacent buildings on shallow-foundation.The monitored wall cracking indicated that structural integrity of these buildings was damaged to different extents.Noticeable post-excavation settlements were observed at adjacent buildings and utility pipelines,due to creeping of soft clay.