Research On Deformation Characteristics Of Existing Shield Tunnel With New Tunnel Construction Based On 3D Discrete-continuous Coupling Method

After more than 40 years of rapid development,China's economy has made remarkable achievements,the process of urbanization is accelerating,a large number of people pour into the city,which has brought tremendous pressure to urban traffic.As a relatively independent underground rail transit system,the Metro forms a three-dimensional urban traffic system with the ground network,which effectively alleviates the problems of large urban traffic congestion.With the continuous improvement of underground traffic network,new tunnels will inevitably pass through various existing structures.If not designed and constructed properly,the existing structures will have large settlement deformation,which will affect the normal operation of existing lines and even lead to major traffic safety accidents.By means of 3D discrete-continuous coupled numerical simulation and field monitoring,the deformation characteristics of existing shield tunnels under construction disturbance are studied,and the defomation and failure law of interlayer soil is analyzed.Taking the tunnel between National Library Station and Erligou Station of Beijing Metro Line 16 underpasses the tunnel between National Library Station and Zoo Station of Existing Metro Line 4 as the engineering background,the results of field monitoring are used to validate the conclusions of the study.The influence of soil mesoscopic parameters on macroscopic mechanical parameters is studied according to the mesoscopic contact properties of particles which need to be set in coupling modeling.The main work and results are as follows:(1)Discrete element method(DEM)is used to study the influence of meso-parameters of sand and clay on macro-mechanical parameters through numerical simulation of triaxial compression tests in laboratory.The linear stiffness model with non-contact bond is used for sand,and its meso-parameters include:contact modulus,stiffness ratio and friction coefficient;the linear parallel bond model with contact bond is used for clay,and its meso-parameters include parallel bond modulus,parallel bond stiffness ratio,parallel bond tensile strength,parallel bond cohesion and parallel bond friction angle besides linear components.The influence rules of each meso-parameter on elastic modulus,Poisson's ratio,cohesion and internal friction angle are obtained,which can provide guidance for selecting appropriate meso-parameters and realizing the calibration of macro-and meso-parameters.(2)PB design method and CCD design method are used to analyze the sensitivity of clay meso-parameters,and the sensitivity ranking of meso-parameters is obtained.The linear regression equation between all meso-parameters and macro-mechanical parameters and the quadratic non-linear regression equation between the two most sensitive meso-parameters and macro-mechanical parameters are obtained.The triaxial compression tests are carried out and the laboratory tests and numerical values are compared and analyzed which verify the calibration results of soil macro and micro parameters.(3)Based on the 3D discrete-continuous coupling method,the numerical model of the new tunnel passing through the existing shield tunnel is established,and the settlement law of the existing tunnel during the whole construction process is studied.The corresponding numerical model is established for the four factors affecting the settlement of the existing tunnel,the thickness of interlayer soil,the depth of the tunnel,the diameter of the new tunnel and the parameters of the stratum,and the influence of these factors on the settlement and deformation of the existing tunnel is analyzed.(4)3D discrete-continuous coupling method is used to study the deformation and failure characteristics of interlayer soil under construction disturbance.The deformation and collapse process of interlayer soil is obtained.The collapse form of interlayer soil is analyzed.The effects of particle size,elastic modulus,Poisson's ratio and internal friction angle on the deformation of interlayer soil and the separation length between interlayer soil and existing tunnel are studied,and the relationship between mechanical parameters of interlayer soil and separation length are obtained.(5)Combining with specific engineering examples,according to the settlement deformation data of existing tunnels monitored on site,the settlement curve is drawn,the settlement law is analyzed,and the numerical simulation analysis of engineering examples is carried out,and the results of field monitoring and numerical simulation analysis are compared to verify the research in this paper.