上软下硬地层深基坑结构变形监测及分析*

为探究在上软下硬地层中进行深基坑开挖时围护结构水平位移与内支撑轴力的变化规律，以广州地区某上软下硬地层盾构井深基坑开挖项目为依托，基于现场监测数据进行分析并运用MIDAS/GTS软件开展深基坑开挖全过程的有限元模拟。将围护结构水平位移模拟值与监测值进行对比，验证模型的准确性；改变围护结构嵌固深度、主体结构厚度等工况，研究上述因素对结构水平位移变化产生的影响。研究结果表明:实测围护结构最大水平位移值11.78 mm，位于长边0.7倍基坑深度附近，坑角处位移值最小；改变结构嵌固深度对坑深15 m以下围护结构位移值影响较大，本工程最佳嵌固深度为1.5~3 m；围护结构水平位移会随着结构主体厚度的增加而减小，但最大位移间差值逐渐减小，结构主体厚度设计值宜为0.8~1 m。

Deformation monitoring and analysis of deep foundation pit structure in upper-soft and lower-hard stratum

In order to explore the variation law of horizontal displacement of retaining structure and axial force of internal support during the deep foundation pit excavation in upper-soft and lower-hard stratum,based on a certain deep foundation pit excavation project of shield well in upper-soft and lower-hard stratum in Guangzhou area,the finite element simulation on the whole process of deep foundation pit excavation was carried out by using the MIDAS/GTS software based on the analysis of field monitoring data.The accuracy of the model was verified by comparing the simulation values and monitoring values of the horizontal displacement of retaining structure,and the influence of the above factors on the structural horizontal displacement was studied by changing the embedded depth of retaining structure,the thickness of main structure and other conditions.The results showed that the measured maximum horizontal displacement of the retaining structure was 11.78 mm,which was located at long edge near 0.7 times of the foundation pit depth,and the displacement value at the corner of the pit was the smallest.Changing the embedded depth of the structure had greater impact on the displacement values of the retaining structure below 15 m of pit depth,and the optimal embedded depth of the project was 1.5~3 m.The horizontal displacement of the retaining structure would decrease with the increase of the main structure thickness,but the difference between maximum displacements would decrease gradually,and the design value of the main structure thickness should be 0.8~1 m.