富水砂卵石地层深基坑开挖变形监测与数值分析

Deformation monitoring and numerical analysis of deep foundation pit excavation in water-rich sandy cobble stratum

以长沙地铁5号线二标晚报大道站富水砂卵石地层深基坑降水开挖工程为依托,在钻孔灌注桩+旋喷桩止水帷幕的设计方案下,首先,给出了该车站深基坑止水帷幕水平位移及周边地表沉降的监测方案,完成了现场监测工作;并根据监测结果分析了止水帷幕水平位移及周边地表沉降随着基坑开挖的变化规律。然后,采用ABAQUS软件对该车站深基坑降水开挖进行了全过程数值模拟,在对止水帷幕水平位移和周边地表沉降模拟值与现场实测值进行对比、验证的基础上,就止水帷幕渗透系数、嵌入岩体深度和横向支撑对止水帷幕水平位移及地表沉降的影响进行了研究。结果表明:横向支撑结构能有效提高基坑稳定性,止水帷幕嵌入岩体深度建议保持在3~7m为宜,可为富水砂卵石地层止水帷幕嵌入岩体深度的合理设计与基坑安全施工提供参考依据。

Relying on dewatering and excavation project of deep foundation pit of Wanbao Dadao station of second bid of Changsha Metro Line 5 in water-rich sandy cobble stratum, under the design plan of bored piled and jet grouting pile water-stop curtain, first, the monitoring scheme for the horizontal displacement of the water-stop curtain and the surrounding surface settlement of deep foundation pit of the station was given and the on-site monitoring work was completed;according to the monitoring results, the change law of the horizontal displacement of the water-stop curtain and the surrounding surface settlement with the excavation of foundation pit was analyzed. Then, the ABAQUS software was used to carry out the whole process numerical simulation of the deep foundation pit dewatering and excavation of the station. On the basis of comparing and verifying simulation value and actual measured value of the horizontal displacement of the water-stop curtain and the surrounding surface settlement, the influence of the permeability coefficient and the depth of the embedded rock mass of the water-stop curtain and the lateral support on the horizontal displacement of the water-stop curtain and the surface settlement were studied. The results show that the lateral support structure can effectively improve the stability of the foundation pit. The depth of embedded rock mass of the water-stop curtain is recommended to be 3~7 m, which can provide reference basis for reasonable design of the depth of embedded rock mass of the water-stop curtain and safe construction of foundation pit in water-rich sandy cobble stratum.