Abstract: To investigate deformation mechanisms and surface settlement patterns of subway deep foundation pit retaining structures under composite geology, this study focuses on a metro station excavation in Changchun through integrated field monitoring and numerical modeling. The foundation pit is located in the terrace geomorphic unit of the alluvial valley. The excavation process of the foundation pit (bored pile with steel support, bored pile with anchor cable) was simulated by MIDAS GTS NX, a finite element simulation software. By comparing the field monitoring data with the numerical simulation results. The variation rules of horizontal displacement and surface settlement of two supporting forms of piles in composite stratum were analyzed.The results show that the horizontal displacement curve of the pile support section shows a “bow” shape with the increase of the depth of foundation pit, which is small at both ends and large in the middle. In the pile-anchor support section, the horizontal displacement of pile body shows a trend of approximate “funnel” shape with the change of foundation pit depth.As the distance from the monitoring point to the edge of the foundation pit increases, the surface settlement value presents a trend of increasing first and then decreasing, and the maximum value appears in the position within 3-5 m from the edge of the foundation pit. Reasonable setting of steel support axial force and anchor cable tension is beneficial to effectively control foundation pit deformation and surface settlement. The numerical simulation results are basically consistent with the change law reflected by the actual monitoring data, which verifies the rationality and reliability of the model. 

Key words:  , valley alluvial terrace, foundation pit excavation, on-site monitoring, finite element numerical simulation, horizontal displacement, surface settlement ,