Study On The Impact Analysis And Control Technology Of Subway Shield Machine Underpassing The Bridge Pile Foundation In Water-Rich Sand Layer

With the development of urban transportation,the use of underground space is receiving more and more attention.Due to the complexity of the urban environment,shield tunnel construction will inevitably cross the foundation of existing bridges.The tunnel shield excavation disturbs the surrounding soil and causes ground deformation,and damages the adjacent bridge pile foundations and superstructure,which can affect the normal use of the bridge in serious cases.Previous studies were mostly on shield crossing 3×2 or 2×2 bridge group pile foundation,but less on shield crossing 8×4 group pile foundation of cable-stayed bridge.Therefore,it is of great engineering importance to study the effect of shield tunneling on complex forms of group pile foundations.This paper takes the side-cutting of the Wanglong West Bridge by the shield of Zhengzhou Metro Line 12 as the background of the project.On the basis of theoretical analysis and numerical calculation,the impact of the shield tunnel construction on the ground and pile foundation is analyzed in comparison with the actual measurement data on site,and specific control measures are proposed,to provide a reference for the construction of similar projects.The main research work of the thesis is as follows:(1)The first 45m of the lake bottom was set as the test section.The shield worked smoothly in the test section and the ground settlement value met the specification requirements.Statistical analysis of the test section data was used to determine the appropriate shield parameters for penetrating the lake bottom.The thrust range of left and right lines is 14000～17000k N.The pressure of the excavation chamber on the left and right lines ranges from 1.4 bar to 1.6bar.The grouting pressure on the left and right lines ranges from 2.0 bar to 3.8bar.The grouting amount ranges from 5.4～7.2 m~3/ring in the process of left and right line tunneling.The driving speed of left and right lines is 30～50mm/min.These parameters provide a reference for the subsequent finite element model parameter selection.(2)The effect of shield construction on the ground and the effect of ground disturbance on the pile foundations are discussed.Analysis of the pile-tunnel-soil interaction mechanism.Studies have shown that shield construction can cause horizontal and vertical deformation of the ground.Horizontal ground deformation causing tilting and flexural deformation of piles adjacent to the pile foundation.Reduced pile bearing capacity due to vertical ground deformation.(3)Numerical modeling of shield crossing bridge pile foundations to study the influence between pile-tunnel-soil.Analysis shows that the closer the shield excavation surface is to the section where the pile foundation is located,the greater the vertical deformation of the pile foundation.Maximum deformation fluctuation when the shield excavation reaches the section where the piles are located.The maximum vertical deformation of abutment pile foundation is 2.09mm,the maximum vertical deformation of pier pile foundation is 2.36mm.The shield away from the pile foundation deformation tends to stabilize.In the direction of vertical tunnel excavation,the upper part of the pile foundation produces displacement against the direction of the tunnel,the maximum horizontal deformation of the abutment pile foundation is2.208mm,the maximum horizontal deformation of the pier pile foundation is 0.767mm,the lower part of the pile foundation produces displacement opposite to the upper part.The horizontal deformation of the later rows of piles and the characteristic values of the pile internal force show a decreasing phenomenon in the process of shield crossing the pile foundation due to the shading effect of the previous row of piles.(4)Combined with engineering examples,the measured data and numerical simulation data on the construction site are compared and analyzed.The results show that the settlement trends are consistent and meet the requirements of the settlement control values.Proposing a number of specific methods to control ground deformation and simulating the"additional pipe slurry holes"method.The results show that the settlement of the strengthened abutment is 26%less than that of the unstrengthened abutment,with a significant strengthening effect.