混合地层盾构超深接收井开挖安全监测分析

Safety monitoring and analysis of shield ultra-deep receiving well excavation in mixed stratum

以南京某过江隧道45.4 m黏土-砂岩混合地层超深盾构井接收基坑为研究对象,结合地质勘察数据及施工日志,对该超深基坑开挖支护过程中的地连墙顶部隆沉、深层侧向变形及立柱隆沉等支护体系实测数据进行分析,探讨该混合地层超深基坑的变形性状。结果表明:当基坑开挖深度小于20 m时各监测点的最大变形位置H m位于0.34 H_(e)~1.28 H_(e)(H_(e)为开挖深度)之间,开挖深度超过20 m时侧向变形位置基本不发生变化;混合地层的开挖对基坑地连墙的深层侧向变形具有较大的影响,黏土地层的开挖具有明显的深度效应,但砂岩地层的开挖深度效应并不明显;案例的地连墙最大水平位移δhm在0.013%H_(e)~0.044%H_(e)之间,位移量较小,支护体系的完整性对地连墙的位移具有较好的抑制作用;当开挖深度较大时,由于承压含水层覆土厚度的降低出现短暂的回弹作用,使得立柱、地连墙出现隆起现象;支护体系的隆沉具有明显的同步相关性。

The 45.4 m ultra-deep shield well receiving foundation pit in clay-sandstone mixed stratum of a Nanjing river-crossing tunnel was used as the research object.Based on geological survey data and construction logs,the measured data of the support system for the excavation and support process of the ultra-deep foundation pit,including the top uplift of the diaphragm wall,deep lateral deformation and column uplift were analyzed.The deformation behavior of the ultra-deep foundation pit in the mixed stratum was discussed.The results show that the position of maximum deformation H m is between 0.34 H_(e)and 1.28 H_(e)(H_(e)is the excavation depth)when the excavation depth of the foundation pit is less than 20 m.The lateral deformation position basically does not change when the excavation depth exceeds 20 m.The excavation of mixed stratum has a great influence on the deep lateral deformation of the diaphragm wall of the foundation pit.The excavation of clay soil layer has obvious depth effect,but the excavation depth effect of sandstone strata is not obvious.In the case,the maximum lateral deformationδhm of diaphragm wall varies between 0.013%H_(e)and 0.044%H_(e),and the displacement is small.The integrity of the supporting system has a good inhibitory effect on the displacement of the diaphragm wall.When the excavation depth is large,the reduction of the thickness of the confined aquifer will cause a short-term rebound effect,which will cause the uplift of the column and the diaphragm wall.The uplift and subsidence stage of the entire support system has obvious synchronization correlation.