Study On Deformation Control Of Existing Subway Tunnels By Close Construction Of Open-cut Tunnels

With the vigorous development of Chinese economy,the urbanization rate and the urban population continued growth,the problems of traffic congestion and land shortage in large cities are becoming more and more serious.The development of urban transportation to underground space has become the trend of the times,and the construction of existing tunnels is near The number of underground engineering projects is increasing,and the construction of new projects will cause the redistribution of soil stress within a certain range to affect the existing tunnel structure.Therefore,this paper will use open-pit excavation of Xinfeng Middle Road underneath the existing subway Line 5 left line,right line of the ring line,left line of the ring line as the engineering support,using theoretical analysis,numerical simulation,on-site monitoring and other methods to study and analyze open excavation The impact of the tunnel construction on the existing subway tunnel and the corresponding deformation control measures,the main research conclusions are as follows:(1)According to the actual situation of the project,the Midas GTS/NX finite element software was used to numerically simulate the foundation pit of Xinfeng Middle Road through several different foundation pit excavation methods.The results show that: the existing subway tunnel structure The vertical displacement,horizontal displacement,and stress all comply with the relevant safety control standards;the left-line tunnel structure of Metro Line 5 located directly under the foundation pit of the underpass is mainly vertical uplift deformation,which is greatly affected by the nearby construction and is located under the The vertical and horizontal deformations of the left and right subway tunnels under the side of the road foundation pit are relatively small;the method of layered and segmented skipping excavation can better control the vertical structure of the existing tunnel during the construction of the adjacent tunnel The rate of change of vertical displacement,horizontal displacement,maximum and minimum principal stress,the foundation pit of Xinfeng Middle Road underpass adopts this method for construction.(2)Modeling and analysis of several commonly used deformation control measures on the deformation control effect of the left line tunnel structure of Line 5,which is greatly affected by the construction of the underpass of Xinfeng Middle Road.The results show that: the measures to strengthen the pit bottom The control effect of structural deformation is not obvious;the maximum vertical and horizontal displacements are reduced by 13.5% and 15.5% respectively by adopting door-type reinforcement measures;the maximum vertical and horizontal displacements are respectively reduced by adopting grouting reinforcement measures in tunnels 21% and30%;the measures of temporary support and backpressure in the tunnel reduced the maximum vertical and horizontal displacement by 17% and 10%,respectively.Due to the long distance of the left line tunnel of Line 5 and the underpass of Xinfeng Middle Road,which are co-located for a long distance and have not been laid,after taking into account the construction period and cost and other factors,temporary support and backpressure in the tunnel are taken for the left line tunnel of Line 5 The structural deformation can be controlled below the alarm value of 7.5mm for this project.(3)During the construction of the approaching tunnel under Xinfeng Middle Road,the measured values of the vertical and horizontal displacements of the tunnel structure on the left line of the fifth line,the right line of the ring line,and the left line of the ring line are all lower than the standard safety control values.Exceeding the alarm value of7.5mm in this project,it is effective to adopt the method of layer-by-section excavation and excavation for the foundation pit of the underpass of Xinfeng Middle Road and the deformation control measures of the left-line tunnel structure of Line 5.(4)By comparing and analyzing the field measurement data of the existing tunnel structure with the numerical simulation results,it is found that the deformation laws of the two are basically the same,and the measured data confirm the validity of the numerical simulation results.