Impact Analysis And Safety Control Research In Shield Tunnel Parallel-crossing Existing Multi-arch Tunnel

In recent years,more and more subway shield tunnels are being constructed to meet the increasing demands of transportation in densely populated urban areas.It is common that the newly-built shield approaching construction the existing tunnels.However,the case of newly-built shield tunnels parallel-crossing existing multi-arch tunnel is still rare.During the construction of multi-arch tunnel structure safety could be affected,which pose a serious challenge to the rapid construction and development of urban rail transit.Therefore,they must be properly dealt with.Based on the project of tunnel between Hangtianxincheng and Hangtiandonglu in Xi'an Metro line 4,the influence law and control measures during shield tunnels parallel-crossing existing multi-arch tunnel were studied by the means of theoretical analysis,numerical calculation and field tests.The main works in this dissertation were as follows:(1)Obtained the elastic displacement and superimposed stress induced both by bulkhead additive thrust and frictional force between shield and soil from the Mindlin solution in elastic mechanics.The superimposed stress generated by ground loss was solved by using theory of image method,the formulas of total soil stress are obtained.Relying the project,displacement on the soil in and superimposed stress in multi-arch tunnel axis and superimposed load in multi-arch tunnel has been systematically studied by MATLAB.(2)Based on the construction of newly-built shield tunnels parallel crossing the existing multi-arch tunnels,a three-dimensional numerical calculation model was established to simulate the soil excavation,the support pressure of tunnel face,grouting pressure and segments assembling through null model,changing the material parameters,and adding or removing the face pressure.The changing laws of internal force and displacement of existing multi-arch tunnels,displacement and force of surrounding soil and surface settlement during shield tunneling were analyzed.(3)Considering different modulus of soil,different tunnel clear distance,different grouting pressure and different chamber earth pressure,the different parameters is analyzed.The surface displacement,lining displacement and internal force of the change of lining is analyzed in detail to find out the degree of parameters influence on the internal force and displacement of surrounding soils to the small tunnel.(4)Based on analyzing and summarizing relevant standards and experience in similar projects at home and abroad,the control standards of existing multi-arch tunnel are given to ensure the safety of existing multi-arch tunnel structure.The parameter calculation and selection of shield crossing construction are introduced in detail.To compare with the statistical data from the 350 th rings to 707 th rings of segments under construction such as the earth pressure,driving speed,grouting pressure,thrust,excavated volume,cutter torque and speed,the calculated parameters are in good agreement with the adopted tunneling parameters when.In addition,the reinforcement measures of soil mass and multi-arch tunnel structure during the construction of shield tunnel parallel crosses multi-arch tunnel in short distance are briefly introduced and analyzed to provide safety control measure for similar crossing project.(5)The monitoring item,section and measuring point,monitoring elements and results have been brief introduced in shield tunnel crossing multi-arch tunnel.Based on the effect of tunnel construction on the buildings in and construction guide in Japan,and combined with change of vertical displacement and pressure stress of concrete in tunnel vault,the method of partition impact are put forward.The effect of shield construction to newly multi-arch tunnel can be effectively partitioned.Finally,the shield tunnel crossing the existing multi-arch tunnel safety,and there are no structural cracks found on the existing tunnel's lining.It show that the construction plan and the control measures are reasonable and can solving the practical problems,which have certain guidance significance to later similar construction project.