Numerical Analysis Of Supporting Structure And Deformation Monitoring Of Pit Excavation In Deep Metro Foundation

At the present stage of development of underground space in China,The deep foundation pit engineering has been emerge in an endless stream in every major city.in order to avoid the accident,designed for retaining structure is too conservative.Based on the deep foundation pit project of the station of HunNanDaDao in Shenyang Subway Line 2,taking the method of combining the real-time monitoring with numerical simulation,I suppose that the design of the original steel support is conservative and I carry out optimum design for it.The following research work has been carried out:(1)Through consulting the literature about the deep foundation pit,According to the development status of deep foundation pit engineering,Combined with the excavation of foundation pit Hunnan Avenue station,The installation process and monitoring scheme of pile horizontal displacement and support axial force are described in detail in this paper.Through the summary analysis of the horizontal displacement of pile,axis force,surface subsidence site monitoring data to conclude that the horizontal displacement curve of the pile shows a parabola shape and the maximum horizontal displacement corresponds to the location of the middle and lower parts of the foundation pit excavation;In the standard section,the maximum supporting axial force appears in the third support,it means that the excavation of the middle and lower parts of the pit;The maximum value of the surface settlement curve is not the closest distance to the foundation pit,but the distance from the foundation pit is about 10m;At the same time,the measured maximum displacement of pile body is only 30%of the control value,the maximum value of steel support axial force is only 26.4%,and the original envelope design is too conservative.(2)In combination with the geological circumstance of Hunnan Avenue station,using the MIDAS/GTS for foundation pit excavation engineering three-dimensional model is established,simulated under different conditions the excavation of foundation pit deformation analysis of retaining structure in the process of simulation of deformation and stress distribution,and compared with the measured values than that pile horizontal displacement simulation value is 28.6%control values,steel support axial force simulation value is less than 40%of control values,analog value is measured worth 78%,validate the rationality of the model,It also shows that the original design is too conservative.(3)Designing parameters through the changing the number of horizontal spacing,steel support pre-tension,steel support and at the end of the first support position to numerical simulation analysis.Calculate the change of different parameters on the change trend of retaining structure,then a new design scheme of steel support is finally determined by analyzing the influence degree of various factors on the foundation pit.The new design scheme reduce the number and level of the steel support spacing,adjust the position of tide and at the end of the first,increasing the additive axial force value,eventually pile maximum displacement increases from 8.57mm to 8.57mm,the maximum control is only worth 32.7%.The simulation results are smaller than the measured results,the measured is worth 76%,according to this ratio to enlarge the simulation value of the new scheme,the control value is 12.86mm which is 42.9%of before,and is still in the control range,so the new design is more reasonable.