| With the acceleration of urbanization,the metro line network will be further improved and formed,and the later metro network in cities will be more intensive,and the existing metro line network will inevitably intersect,cross and orthogonal with the later planned metro line.At that time,the construction of the metro project in the later stage will produce additional stress and deformation to the soil around the existing metro tunnel structure,which will lead to the deformation of the existing metro tunnel structure.Therefore,it is necessary to study and analyze the deformation and stress law of existing metro tunnels caused by soil excavation unloading and explore the control measures to reduce the deformation of existing metro tunnels.On this basis,taking the project of Xi’an Metro Line 8 crossing the existing Metro Line 5 as the background,the factors affecting the deformation stability of the existing metro tunnel are explored,and emphasis is laid on the analysis of deformation and stress characteristics of existing metro tunnel structures strengthened by advanced pipe curtain and anti-floating anchor cable under conditions of shield excavation unloading.On this basis,the reinforcement effect of advance pipe curtain and anti-floating anchor cable on existing metro tunnel under different reinforcement measures is further analyzed.The main conclusions are as follows:1.Considering comprehensively the engineering geological conditions,scale,construction scheme and spatial location relationship between the newly built metro tunnel and the existing metro,the influence degree of the new construction disturbance on the existing metro structure is divided into four grades: non-influential scope,attention scope,scope of measures taken and scope of careful consideration.Based on the statistical analysis of the existing construction disturbance cases in China,the main factors tunnel construction affects the existing subway structure are obtained.In addition,the deformation mechanism of existing metro tunnel structure caused by shield tunneling through and unloading is analyzed through the mechanism of deformation force transmission.2.On the basis of simplifying the practical engineering,through numerical simulation and orthogonal test,the influence degree of different factors on the stability of existing metro tunnels in the process of new shield tunnels passing through existing metro tunnels is analyzed and studied.Taking the vault uplift value and radial relative displacement of existing tunnels as test and evaluation criteria,it is concluded that the diameter of newly built shield tunnels(unloading area above)has the greatest influence on the stability of existing metro tunnels and the thickness of interlayer soil between new tunnel and existing metro tunnel has the greatest influence on the stability of existing metro tunnel when the vault moment of existing tunnel is taken as evaluation standard.From the overall level of new shield tunnels passing through existing metro tunnels,the diameter of new shield tunnels(upper unloading area)has a greater impact on the stability of existing metro tunnels than the thickness of sandwich soil.In addition,the angle between new shield tunnels and existing tunnels has no significant impact on the stability of existing tunnels.3.The elastic modulus of the soil around the existing metro tunnel is improved to a certain extent by adopting comprehensive measures of advanced pipe curtain and anti-floating anchor cable,which avoids excessive uplift deformation of the tunnel and ensures the safety of operating metro.After the completion of shield unloading,the maximum uplift of the existing metro tunnel is 9.21 mm on the right and 9.08 mm on the left,which meets the safety control standard value of the existing metro.It shows that the longitudinal stiffness of existing metro tunnels can be improved and the stability of tunnels can be improved after the comprehensive measures of advanced pipe curtain and anti-floating anchor cable are strengthened,which has a good effect on restraining the deformation of existing metro tunnels and guarantees the safety of operating metro to a great extent.4.Through the establishment of four working mode models,which are no reinforcement measures,only advanced pipe curtain reinforcement,only anti-floating anchor cable reinforcement and comprehensive reinforcement of advanced pipe curtain and anti-floating anchor cable,Emphasis is laid on the analysis of the vertical displacement of arch top,vertical displacement of tunnel bottom and horizontal displacement of side wall of existing metro tunnels under various working conditions.The effect of advance pipe curtain and anti-floating anchor cable on existing metro tunnels under different reinforcement conditions is studied,and the reinforcement method of existing metro tunnels is optimized.Statistical data of advanced pipe curtain and anti-floating anchor cable to reduce the deformation of existing metro tunnels are collected.The reinforcement effect of three reinforcement conditions on the deformation of existing metro tunnels is studied.The results show that anti-floating anchor cable has obvious effect on restraining the vertical deformation of existing metro tunnels,and the effect of advanced pipe curtain on restraining the horizontal deformation of existing metro tunnels is obvious. |
