Study On Mechanical Deformation Characteristics And Geometric Configuration Of Ring Beam Inner Bracing In Soft Soil Foundation Pit

With the increase of high-rise buildings and underground projects in China,foundation pit projects are emerging.The foundation pit engineering has strong regional characteristics.In view of the research on the mechanical deformation characteristics and geometric configuration of the inner support of the ring beam in the soft soil foundation pit,this paper relies on a ring beam supporting foundation pit engineering in the soft soil area,and uses the methods of mathematical statistics,monitoring data analysis and numerical calculation to carry out relevant research.The specific research contents and results are as follows:(1)This paper summarizes the engineering characteristics of soft soil stratum and the engineering geological problems of foundation pit in China.Through the statistical analysis of 32 completed urban foundation pit engineering data in soft soil area,it can be seen that:the type of retaining structure of soft soil foundation pit is mainly underground continuous wall and cast-in-place pile;When the excavation depth is less than 16m,the maximum lateral deformation of the retaining structure is 0.5 Hand 1.0H.when the excavation depth is more than 16m,the maximum lateral deformation is distributed near the pit bottom;The inner support of ring girder can be flexibly arranged under different excavation surfaces with the excavation depth less than 15m,and it can provide a larger construction surface compared with the combination of opposite support and angle support.(2)Based on the engineering data,a standardized numerical calculation model is established.From the calculation results,it can be seen that:the lateral deformation of the retaining structure is "bulging belly" distribution,in which the maximum lateral deformation is located near the middle of the foundation pit,and gradually moves downward with the increase of the excavation depth;during the excavation of the foundation pit,the surrounding surface settlement does not always maintain a single settlement feature,but opens with the soil mass The increase of excavation shows a dynamic change,and the final transition to "groove type".Under the influence of "pit angle effect",the ground settlement near the middle of the foundation pit is larger than that at the pit corners on both sides;for the inner support of the same ring beam,the axial force increases gradually from the outside to the inside,and the deformation decreases gradually;by comparing the numerical calculation results of the excavation of the inner support of the ring beam with the monitoring data,it is found that the two are in good agreement,and the change trend is basically the same,which verifies the Correctness of numerical calculation model.(3)Based on the verified model,the numerical analysis of the excavation of the foundation pit is carried out.The results show that the deformation of the retaining structure is close to the surface settlement,the axial force distribution of the ring beam support is more uniform than that of the combination of the opposite brace and angle brace,the stress system is clear,and the economic applicability is better.(4)The influence of angle brace,radial brace,ring beam diameter and number on the support stress and deformation is analyzed.The results show that the reasonable setting of angle brace and radiation brace can increase the local stiffness of brace to a certain extent and improve the local deformation resistance of brace;the increase of ring beam diameter will reduce the support stiffness,weaken the circular arch effect and decrease the deformation resistance of brace;with the increase of ring beam number,the overall stiffness of brace will increase,the arch effect will increase,and the axial force and deformation of brace will decrease obviously small,and the decrease range increases gradually.