Research On The Deformation Of Subway Tunnel Caused By Large-area Piling,unloading And Foundation Pit Excavation

With the development of urban underground space engineering,the load changes around existing subway tunnel lines are becoming more and more complicated.The impact of external load changes on the deformation of adjacent subway tunnels has become a key technical issue that cannot be ignored in the development and utilization of urban underground space.At present,extensive research has been conducted at home and abroad mainly on the influence of the single loading or unloading of the neighboring existing tunnels,and the whole process of construction under the superposition effect of loading and unloading considering the material properties of viscoelastic plastic materials under site engineering geological conditions Research on the influence of existing tunnels on deformation is still relatively rare.In this paper,the finite element method is used,and the finite element software Midas GTS is used to establish a three-dimensional numerical model based on an underground space engineering case in the eastern area of Zhengzhou to simulate and study the impact of pile loading,soil unloading and superimposed foundation pit excavation on the deformation of the existing tunnel below.The main research content and conclusions are as follows:(1)Analysis of pile height during pile loading and unloading,length of pile piles along the horizontal and vertical direction of the tunnel,horizontal distance between pile foot and tunnel,and vertical distance between pile and tunnel.Influence on the deformation law of the tunnel.The research shows that the pile height has a significant effect on tunnel deformation relative to other factors.After unloading the pile,the residual deformation ratio of the tunnel increases with the increase of the pile height;when the pile length to height ratio is the same,the tunnel under different pile heights The deformation rates are equal.With the increase of the length-to-height ratio,the tunnel deformation gradually stabilizes from the increase;the horizontal deformation trend of the different end points of the tunnel is closely related to the relative horizontal position of the pile and the tunnel;the horizontal and vertical displacements of the tunnel follow the pile The vertical distance from the tunnel increases and decreases.(2)Analyze the influence of factors such as the horizontal clear distance between the foundation pit and the tunnel during excavation,the excavation depth of the foundation pit,the depth of the tunnel and the surrounding structure of the foundation pit on the deformation law of the tunnel.The research shows that with the increase of the horizontal distance between the foundation pit and the tunnel,the tunnel deformation gradually decreases,the direction of the total displacement vector of the tunnel has a counterclockwise rotation trend,and the maximum deformation position is getting closer to the left arch waist;when the excavation depth is different The deformation of the tunnel is closely related to the deformation of the ground connection wall;due to the different vertical positions of the pit bottom and the tunnel,the vertical displacement of the tunnel produces different deformations of uplift or settlement;the thickness of the ground connection wall and the insertion ratio have little effect on the tunnel deformation.(3)When the relative spatial position relationship between the piled soil and the foundation pit and the existing tunnel is different,establish four different stacking modes of the piled soil and the foundation pit,and analyze the Vertical and elongation convergence deformation.The research shows that the pile-excavation excavation directly above can restore the final deformation of the tunnel to its initial state.Under different stacking modes,the maximum vertical displacement of the tunnel occurs during the loading phase of the pile,and the maximum horizontal displacement and convergence deformation occur in the pile.Loading or unloading side of foundation pit.(4)Simulate and analyze the three-dimensional space model of an engineering project to obtain the vertical and horizontal deformation laws of the tunnel and the changes of bending moments during the whole process of pile-up loading and unloading superimposed foundation pit excavation and unloading.The research shows that the impact of loading and unloading directly above the tunnel is much greater than that of the lateral loading and unloading.The impact of the pile loading and unloading phase on the tunnel is mainly vertical deformation.The relative position of the tunnel is related;the tunnel structure cannot be restored to its original state after being loaded and unloaded by the earth pile,and the bending moment curve of the tunnel center section is roughly distributed in gourd shape;the numerical simulation results are compared with the measured values to verify the establishment of the finite element model.Effectiveness,combined with engineering example results,proposed tunnel protection measures.