Study On Temperature Effect Of Steel Bracing In Deep Foundation Pit

With the acceleration of urbanization in China,the utilization rate of urban underground space is more and more high,the deep and large foundation pit is more and more,how to effectively control the deformation of foundation pit and its supporting structure is the focus of foundation pit Engineering,the support mode of cast-in-place pile plus steel support is more and more extensive because of its costeffective use.The monitoring of steel support axial force is very important to the feedback of foundation pit deformation,and the method of optimizing the monitoring and calculation of steel support axial force and eliminating the influence of temperature factors are of great benefit to guide the construction.Based on the excavation of the foundation pit of the new station of Beijing Metro line Line 19,this paper uses FLAC3 D finite difference software to simulate,calculates according to the actual excavation support process,compares and analyzes the actual monitoring data as the basis,and determines the reliability of the simulation model for the research content.On the basis of reliability,the influence of temperature factors is predicted,and the monitoring mode of steel support axial force is optimized,the concrete conclusions are as follows:1.The calculation model of FLAC3 D Foundation Pit excavation support for the main foundation pit project of the new Land station of Beijing Metro line Line 19 is established,and the simulation results are in good agreement with the actual monitoring data.2.Through field tests,the changing coefficients of the axial force gauges for different ranges of steel support axial force monitoring used in the foundation pit engineering of the new ground station are given,as well as the changing coefficients of the steel support used in the foundation pit support of the project.3.Taking the calculation model after excavation as the carrier,simulating the influence of the additional axial force caused by temperature change on the surface subsidence displacement and the horizontal displacement of the pile in other monitoring items by applying the additional axial force,and concludes that the influence of the additional axial force of the steel support caused by the temperature change on other monitoring items can be ignored.4.On the premise of conclusion 2 and 3,in order to avoid the large discrepancy between the construction party and the third party monitoring data caused by different monitoring time and different temperature,which affects the progress of the project,the comparison and correction formula of the axial force calculation on the Steel Support Axial Force monitoring project is put forward.5.The formula can also be used according to the seasonal temperature in the construction unit erection of steel support,or when the temperature change is large for the construction unit to provide steel support erection and adjust the steel support axial force value of the data,to prevent the appearance of the steel support Axial force monitoring negative situation,The first layer of steel support,which is significantly affected by temperature,should take sunscreen measures,especially when the temperature is high in summer,such as wrapping a layer of reed made of reeds on the surface of the steel support when the steel support is erected.