Influence Of Foundation Pit Excavation On Adjacent Tunnel Deformation And Control Analysis

In recent years,the emergence of subway tunnels has effectively alleviated urban traffic congestion,and the construction boom of major cities has sprung up.At the same time,a large number of foundation pit projects are located around the tunnel,which leads to the occurrence of adjacent construction of foundation pit in subway tunnels,and the unloading of foundation pit will inevitably cause adverse effects on adjacent subway tunnels.Therefore,the analysis of the influence of foundation pit excavation on adjacent tunnels is of great significance to the safe operation of subway tunnels.In this paper,based on the theory of foundation pit excavation deformation mechanism and tunnel deformation mechanism,relying on a deep foundation pit adjacent to the subway line 3 interval tunnel project in Hefei as the background,through numerical simulation method and field measurement method,summarizes the influence of foundation pit excavation on adjacent tunnel displacement,and using the control variable method,analyzes the control effect of different retaining structure thickness,different internal support stiffness,different foundation pit excavation methods and isolation pile position,pile length,pile diameter on adjacent tunnel displacement.The main research contents and results are as follows :（1）The current situation of deformation of adjacent tunnels caused by foundation pit excavation at home and abroad is summarized,and the relevant mechanism of foundation pit excavation deformation and tunnel deformation and the existing control measures of tunnel deformation are summarized.（2）The surface settlement is mainly concentrated around the foundation pit,and the settlement at the pit corner is small,and the maximum value occurs at 11 m away from the edge of the foundation pit,namely 0.68H（H is the excavation depth of the foundation pit）;the influence range of surface subsidence is 2H,the value of surface subsidence beyond the influence range is small,and the overall deformation form is ’groove’;the horizontal displacement of retaining structure mainly occurs in the upper part of the pile,and the maximum position occurs at 7m from the top of the retaining structure,that is 0.43 H.The overall deformation form is ’composite’ along the depth direction.（3）With the increase of foundation pit unloading,the horizontal and vertical displacement of the tunnel showed an obvious increasing trend,and the maximum displacement occurred at the middle position of the left arch waist and the vault of the tunnel,respectively,and the foundation pit unloading had a great influence on the horizontal displacement of the tunnel.Affected by the excavation range of foundation pit,the horizontal and vertical displacement of the tunnel presents a ’normal distribution’ deformation form.The displacement of the tunnel increases faster and the deformation is larger in the excavation range.The displacement of the tunnel increases slowly and the deformation is small outside the excavation range.Comparing the numerical simulation results with the actual monitoring results,it is found that they are basically the same in the numerical size and change trend,indicating that the model established in this paper can reflect the displacement change of the adjacent tunnel caused by foundation pit excavation.（4）The results of single control variable analysis show that the thickness of enclosure structure has weak control on tunnel deformation.When the thickness of enclosure structure increases from 0.5m to 1.5m,the maximum horizontal and vertical displacement of tunnel decrease by 12.7% and 7.6% respectively.The increase of support stiffness has better control on the horizontal displacement of the tunnel,but has no obvious control effect on the vertical displacement of the tunnel.When the support section size increases from 0.4m×0.4m to1.0m×1.0m,the maximum horizontal and vertical displacement of the tunnel decreases by19.06% and 9.54%,respectively.When the foundation pit is excavated by partition,the soil far from the tunnel side should be excavated first,and the maximum horizontal and vertical displacement of the tunnel can be reduced by 33% and 39.4%,respectively.The isolation pile should be set near the tunnel side.Compared with the condition without isolation pile,the horizontal displacement of the tunnel can be reduced by 30% when the isolation pile is set at 2m away from the tunnel.Increasing pile length and pile diameter can reduce the horizontal displacement of the tunnel,but the control effect of pile length is stronger than that of pile diameter.When the pile length increases from 16 m to 26 m,the horizontal displacement of the tunnel can be reduced by 26.4%,and when the pile diameter increases from 0.6m to 1.4m,the horizontal displacement of the tunnel can be reduced by 15.6%.Figure [47] Table [9] Reference [58]...