| For the construction of cross-transit stations,the excavation of the foundation pit of the post-built station will inevitably have a certain impact on the already operated stations.Therefore,how to ensure the safe operation of existing stations during the construction of the foundation pit project has become an urgent problem to be solved in subway construction.Based on the research background of the foundation pit project of the new station in the cross transfer station of Zhengzhou Rail Transit Line1 and line 5,the material parameters were selected based on the engineering survey data,and the three-dimensional numerical model was established using the general geotechnical finite element software Midas GTS NX.Study and analyze the influence of foundation pit excavation on the structural deformation of adjacent metro station structure with or without horizontal braces,and focuses on the feasibility of the measured scheme(elimination of horizontal braces).The excavation method of foundation pit was presented.Combined with the field measurement data,the numerical analysis parameters are updated one by one to ensure the safety of the construction process of the example project based on the principle of information construction.In this paper,the supporting scheme with horizontal braces is named as“original scheme”,abbreviated as “scheme 0”;the supporting scheme without horizontal braces is named as “optimization scheme”,and is referred to as “scheme1”.The main research contents and conclusions are as follows:(1)In the weak stratum,the bored pile is used as the maintenance structure.The soil in the foundation pit was excavated in blocks and layers,and the foundation pit needs to be supported in time.This construction technology can make the deformation of the operation station meet the requirements,and effectively ensure the safety of the existing operation station.(2)In scheme 0 and scheme 1,the deformation law of the adjacent existing subway station structure is basically the same,the maximum horizontal displacement occurs in the side wall of the excavation of the foundation pit,the maximum vertical displacement occurs in the top plate of the station structure,and the existing subway station structure is dominated by vertical displacement.The maximum horizontal displacement of the second basement of the existing station structure occurs at the outermost side of the excavation side of the adjacent foundation pit,and the maximum vertical displacement occurs at the station floor on the longitudinal side of the transfer node(longitudinal of Line 1 station).(3)In scheme 0,the excavation of foundation pit has no effect on the vertical displacement control of the existing subway station structure,and has little effect on the horizontal displacement control.After excavation of the foundation pit with or without horizontal diagonal braces,the horizontal and vertical displacement values of the adjacent subway station structure are less than ± 5mm of the safety control warning value,meeting the limit requirements.Considering the construction process,engineering cost,safety control and other factors,this paper optimizes the supporting scheme of the foundation pit with horizontal diagonal braces,and cancels the horizontal diagonal braces in the supporting scheme of the foundation pit.(4)During the excavation of the foundation pit with scheme 1,the whole process of the adjacent existing subway station structure is monitored on site,and the numerical analysis parameters are updated and checked one by one to ensure the construction safety with the information construction technology.The results show that after the excavation of the foundation pit is completed,the maximum vertical displacement value of the structure adjacent to the existing subway station is 2.82 mm,the maximum horizontal displacement value is 2.71 mm,and the deformation values are less than the safety control warning value ± 5mm,which meets the limit,and verifies the feasibility of scheme 1.(5)There are a lot of uncertainty factors in the course of optimization for the excavation shoring structure designing.Practically the excavation process may be divided into several key steps.With on the Information-based-construction philosophy,the numerical analysis results are compared with the onsite obtained deformation results,and only if they are close enough,is the optimization design reliable. |
