Influence Of Excavation On The Structure Of Underlying Existing Metro Shield Tunnel

In recent years,the construction of urban rail transit facilities is becoming more and more prosperous,and the mutual influence between new and old projects is becoming more and more obvious.The excavation construction situation of existing metro station and above the tunnel is obviously increased,and the distance between the existing tunnel and the excavation construction scope may be very small.If the appropriate control measures are not taken,it may bring potential safety risks to the existing metro station and tunnel.Based on the box culvert excavation project above a station of Changzhou rail line 1,this paper studies the influence of the excavation of the foundation pit on the structure of the existing underground station and shield tunnel.The main research contents and achievements of this paper are as follows:(1)Based on the summary of literature,the deformation control standard of existing rail transit tunnel of Changzhou rail line 1 is put forward.The deformation of the underpass tunnel caused by the excavation of box culvert above the tourism school station of the North track line 1of Nenjiang road in Changzhou City is monitored.The measured data are summarized and sorted out,and the variation law of the vertical displacement,relative displacement of the tunnel and the vertical displacement of the track bed with time is analyzed.(2)Based on the field engineering data,the influence of the excavation of the upper box culvert on the existing subway station below is studied by numerical simulation.The calculation results show that the displacement and deformation of the subway station structure meet the deformation control standard proposed in this paper.(3)The comparison between the field data and the numerical simulation results shows that the displacement and deformation of the tunnel have a good correspondence with the construction process of the upper part,and the displacement and deformation trend are in line with the trend of the numerical simulation results;The displacement calculated by numerical calculation is slightly smaller than the measured data,which is mainly caused by the difference between the stiffness of tunnel structure and the contact parameters of tunnel soil and the actual situation.(4)The influence of excavation depth and width on the displacement and deformation of the existing tunnel is studied by numerical simulation.The excavation depth and width of the foundation pit increase,and the displacement and deformation of the tunnel will increase,and the excavation depth of the foundation pit is the main influencing factor;The deformation shape of tunnel caused by excavation is the ellipse of vertical stretching and horizontal contraction;The increase of excavation depth and width of foundation pit will make the maximum deformation position of tunnel horizontal move down to the horizontal center line of tunnel to some extent.(5)The influence of the stiffness of tunnel structure and the contact strength of tunnel soil on the displacement and deformation of the tunnel is studied by numerical simulation.In a certain range,the influence of the contact strength between the tunnel structure stiffness and the tunnel soil on the vertical displacement in the middle of the tunnel is very limited;The vertical displacement in the middle of the tunnel can be slightly reduced by increasing the structural stiffness of the tunnel,but it will lead to the slight increase of the horizontal deformation of the tunnel;The horizontal deformation of tunnel can be reduced by increasing the contact strength of tunnel soil in a certain range.