Analysis On The Monitor And Numerical Simulation Of Pit-in-pit Foundation Pit Excavation Of A Subway Station In Lanzhou

This paper mainly aims at the pile-support structure commonly used in the foundation pit of Lanzhou subway station.Using the method of numerical simulation and field monitoring,combined with engineering examples,the factors influencing the deformation,internal force and stability of foundation pit are analyzed.The main contents of this paper are as follows:(1)Based on the foundation pit supporting project of a pit-in-pit subway station in Lanzhou and combined with the specific support type of the foundation pit,the different support types of traditional foundation pit and pit-in-pit type foundation pit are analyzed,which can provide some help for the same pit-in-pit type foundation pit.(2)Field monitoring tests were carried out to analysis the deformation of foundation pit and the internal force and displacement of supporting structure.In this paper,the settlement of buildings around the foundation pit,the settlement of surrounding pipelines,the displacement of pile body and the axial force of internal support are monitored.Through the analysis of monitoring data,the influence of foundation pit excavation on surrounding buildings and pipe-line deformation,and the change of internal force and deformation of surrounding structures during the excavation of pit-in-pit are obtained.(3)Based on Plaxis 3D finite element software and an example of foundation pit support of a subway station in Lanzhou,the foundation pit excavation support model was established.And then the finite element calculation is carried out.According to the calculation results,the horizontal and vertical displacement of surrounding soil and the horizontal displacement of deep soil during excavation are analyzed.In addition,a supporting pile was selected for the comparative analysis of deformation and stress on the pit side and the no-pit side respectively,and the influence of pit excavation on the lateral displacement of the supporting structure was obtained.(4)The actual monitoring data and finite element calculation results are compared and analyzed to show the correctness and reliability of the analysis results.In this paper,the monitoring values of horizontal displacement of pile,settlement of pile top,settlement of ground surface,settlement of building and axial force of internal support are compared with the results of finite element calculation.The comparison results show that the results obtained by the two methods are basically the same,which indicates that the monitoring scheme and the numerical simulation parameters adopted in this paper are correct and the analysis results are reliable to some extent.