Research On The Influence And Control Of Shield Up-passing Construction On The Deformation Of Existing Subway Tunnel

With the rapid development of urban rail transit in China,there are more and more cases of new shield tunnels passing through existing metro lines at short distance.Because the shield tunneling will break the stress balance of the existing line,resulting in longitudinal deformation of the underlying tunnel,and even lead to segment cracking,dislocation and other diseases,which seriously threaten the safe operation of the existing metro.Therefore,based on the science and technology plan project of Hunan Provincial Department of housing and urban rural development(no.ky201943),this paper adopts the methods of engineering investigation,theoretical analysis,numerical simulation and on-site monitoring to study the stress deformation law and its control measures of the shield tunnel construction on the existing metro shield tunnel,so as to provide theoretical support and engineering guidance for the safe construction of new projects and the normal operation of existing lines.The main research work is as follows:(1)Based on Mindlin solution,the distribution form of each additional stress during shield tunneling is analyzed.It is found that the main affected area of the existing tunnel is 2D below the unloading surface;The thickness of interlayer soil is the controlling factor affecting the construction of existing tunnel.(2)Taking the existing tunnel as a series of short beams on Pasternak foundation,considering the rotation effect and shear effect between segments and the interaction between segments and soil,a calculation method for the longitudinal deformation of the existing tunnel is established based on the principle of minimum potential energy.Combined with the engineering calculation,it is shown that the deformation of the existing tunnel decreases greatly with the increase of shear stiffness,tensile stiffness,elastic modulus of stratum and clear distance of the tunnel;The reduction of crossing angle will increase the influence range on the existing line;The tensile stiffness has little effect on the deformation of the existing line;The compression stiffness between rings has almost no effect on the deformation of the tunnel.(3)Through the establishment of a three-dimensional numerical model,the force and deformation development law of the existing line during shield construction is analyzed,and the main affected areas of the existing line are divided into 2D areas on the left and right of the center line;The reinforcement effect in the tunnel shows that the deformation distribution law of the existing line is the same after the reinforcement of the supporting structure with different ring numbers,and the effect of increasing the number of reinforcement rings after more than 5 rings is not obvious.(4)Through the symmetrical arrangement of support and reinforcement structures at the upper crossing,and the control during shield tunneling: the earth bunker pressure is 90～110kpa,the cutter head torque is 2540～3270 KN·m,the tunneling speed is 16～18mm/min,the grouting pressure is 200～300kpa,and the automatic monitoring is adopted for the whole construction process.The maximum vertical displacement of the existing line is only 1.3mm,which is far lower than the corresponding control standard.