Study On Mechanical Effect Of Support Pile At The Interface Between Open And Subsurface Excavation

This paper proposed a tunnel dug at the interface of the physical shading supporting pile structure model,taking an open and subsurface excavation project of the railway station in Chongqing as an example,based on summarizing the engineering characteristics.In order to providing reference for the design and construction of such projects,numerical simulation,structural mechanics and elastic mechanics theory are used to research the mechanical effects of pit support piles at tunnel interface in this paper,combined with on.site monitoring results.Conclusion has been made as follows:（1）Based on the physical generalized model of the supporting pile structure at the interface between open and subsurface excavation,the numerical simulation analysis is carried out by using FLAC^3D finite difference software.The rationality of the numerical simulation analysis is verified by comparing the numerical simulation results with the field monitoring data.（2）According to the established numerical model,considering the influence of the spacing of retaining piles,the size of pile cross section and the shape of pile cross section on the mechanical effect of retaining piles.The results show that the size of pile cross section has the most significant effect on the deformation and mechanical effect of pile.（3）Considering the influence of tunnel diameter,buried depth and direction on the mechanical effect of supporting piles,the results show that the diameter of tunnel has a great influence on the deformation of supporting piles;the change of buried depth will change the position of displacement and internal force extremum of pile body;and the change of tunnel path has a great influence on the shear force of pile body near the top of tunnel.（4）The settlement of slope top and lateral displacement can be effectively reduced by excavating tunnel first and then excavating foundation pit,and the bending moment and shear force of pile body are also small.The arch connecting beam can effectively enhance the supporting effect of remaining piles after the construction of cut.off piles.（5）According to the stress characteristics of supporting piles at the interface between open and underground excavation in tunnels,the finite element method of bar system based on elastic foundation beams and the corresponding structural design flow are proposed to carry out the structural design calculation of supporting structures.The rapid automation of internal force calculation is realized by using MATLAB programming software,and the comparison and analysis of the results with those calculated by Lizheng geotechnical software are carried out.The analysis results show that this method has good adaptability for supporting residual piles under local suspension condition caused by excavation of buried tunnels.