Study On Stress Characteristics Of Annular Support Under Uneven Horizontal Loads

Annular support is a new style of bracing structure,which is under development and more and more widely used in foundation pit engineering.Compared with other forms of foundation pit supports,it combines the advantages such as well stress performance,safety and stability,convenience to construct,shorter construction period and convenience to remove.In the design of annular support,the circular horizontal support is used to take the place of the conventional cruciform layout of bracing structure.When uniformly compressed,the annular support can best exert its performance advantages.Annular support is particularly suitable for foundation pit projects with a weak foundation and a narrow site.In this paper,the development process and research status of the annular support structure in China are summarized,and the components,plane layouts and characteristics of the annular support structure are also summarized.Focusing on the solution of the stress of the annular support structure under uneven loads,and by taking the annular support structure project of the Tianhe Park Station as an example,the internal force of the inner supporting structure under eccentric loads is calculated and analyzed,which provides the reference basis for the design and construction of the annular support structure.The specific contents of this study are as follows:(1)Based on the analysis of the internal force of annular support under uniform loads,the stress characteristics of annular support under uneven horizontal loads are deeply studied,and the stress solution of annular support under the uneven loads is derived.(2)Through practical engineering examples,the stress magnitudes on the annular support cross section under the effects of uneven surface loads,groundwater level variation and other factors are solved.It is found that the annular support under eccentric loads may generate large tensile stress,and it is proposed that the progress of foundation pit excavation should be symmetrical and balanced,the loads surrounding the foundation pit should be strictly controlled,and the monitoring of the underground water level and the dewatering should be cautiously done,which are all construction advice to minimize the adverse effects of uneven loading and groundwater level on the annular support.(3)The stress of annular support section obtained by Midas finite element simulation is compared with that of manual calculation,which proves that the stress solution proposed in this paper is reasonable.Based on the statistical analysis of the monitoring data of the axial force of the annular support of the Tianhe Park Station foundation pit project and the simulation results of Midas finite element software,the variation trend and the influencing factors of axial force of annular support during foundation pit excavation are summarized.The results of numerical simulations for each construction stage were found to be roughly consistent with the actual monitoring data,and it is pointed out that the cross-sectional dimensions of the second and the third annular support could be appropriately reduced,as advice for design optimization of this foundation pit project.