Research On Stiffness Of Annular Bracing And Deformation In Deep Foundation Pits

In the foundation pit support system,the internal bracing structure plays an important role in restricting the foundation pit deformation,and the research on the stiffness calculation of the inner bracing system has been paid more attention by researchers.The calculation formula of horizontal stiffness of bracing is given in the design code,but more and more circular inner braces have no definite stiffness calculation formula,which brings great inconvenience to the design and application.Therefore,the research on the stiffness of annular inner bracing is of great practical significance to foundation pit engineering.Based on the basic definition of stiffness,the formula for calculating the stiffness of annular inner braces is derived in this paper.Based on the engineering examples,the accuracy of the formula for calculating the stiffness of annular inner bracing is verified by comparing the analysis results of Lizheng deep foundation pit software and Midas GTS with the actual monitoring data.The influence of the position of the inner bracing,the size of the section and the prestress on the deformation of the foundation pit is analyzed by Midas GTS.The main work of this article are as follows.(1)In this paper,the derivation process of the formula for calculating the bracing stiffness is studied,and the formula for calculating the internal bracing stiffness of the ring is derived according to the basic definition of the stiffness.(2)The deformation characteristics of the foundation pit are studied by collecting the monitoring data of the foundation pit and processing the data into a graph.(3)The section of foundation pit is calculated with Lizheng deep foundation pit,the stiffness parameters of anchor are calculated by calculating formula,the other parameters areselected by original design data,and the calculation results are compared with the actual monitoring data to verify the accuracy of the stiffness calculation formula.(4)The three-dimensional finite element model of the inner bracing system is established.The overall stiffness of the ring braces is obtained by linear static analysis and the results are compared with the analytical results.Then the two-dimensional finite element model of the equivalent inner braced foundation pit is established,and the accuracy of the calculation formula of the ring inner bracing stiffness is further verified by analyzing the displacement cloud map and comparing the actual monitoring data of the foundation pit.On the basis of this,the influence of internal bracing cross-section size,layout and prestress on foundation pit deformation is studied.