Investigation On The Damage Mechanism And Engineering Application Of Surrounding Rock In Deep Tunnel Based On Cross Scale

Tunnel engineering has a profound influence in the national strategic deployment.However,in order to ensure the stability of tunnel structure and prevent the engineering disaster caused by the deformation of surrounding rock,it is necessary to analyze the deformation law and damage mechanism of surrounding rock on different scales.The continuous-discrete coupled numerical simulation method can be effectively applied to the cross-scale study of rock mass.Therefore,this paper innovatively proposes to introduce the coupling simulation method of transition zone,applying the coupling simulation method with transition zone in laboratory scale and engineering scale to study the deformation and damage mechanism of deep tunnel surrounding rock at different scales.The main contents of this paper are as follows:（1）The energy reflection on the interface between finite element region（Ω_F）and discrete element region（Ω_D）will affect the accuracy of numerical simulation.Therefore,this paper proposes a numerical simulation model named D-DF-F,which is based on the principle of virtual displacement,then introduces the contribution functionα（x）,which can generate a transition regionΩ_DF containing both finite element mesh and discrete element particles at the contact position.The coupling simulation method is optimized to a certain extent,and the stable connection between the two subdomains is realized.The Lagrange multiplier method is used to impose kinematic constraints on the discrete elements of particles and the discrete elements of finite mesh at the same position.Finally,the rationality of the model optimization is verified by taking the straight rod motion problem as an example.（2）This paper investigates the damage and deformation of surrounding rock in laboratory scale.Four point bending tests of granite-shotcrete composite structure beams were designed and carried out.This test used two kinds of granite materials with different mechanical properties and two types of shotcrete materials are C25 and C50 respectively,then testing the material parameters and making test specimens.Through the MTS test machine,it is observed that the macro cracks initiate and propagate at the mid span position.The load-crack width（COD）curve of the composite specimen in the bending failure process is measured.Combined with the physical relationship,geometric relationship and static relationship,the approximate equation of the bending deformation curve at the mid span position is derived,and summarized the deformation mechanism of bending failure of granite-shotcrete composite structure beam.（3）The macro and micro parameters fitting of materials are carried out by the PFC^3Dsoftware.The sensitivity analysis of the influence of each micro parameter is carried out by uniaxial compression calibration method,and the fitting law equation is summarized.Finally,the micro mechanical parameters of each material are determined.The D-DF-F model is established by FLAC^3D and PFC^3Dsoftware to simulate the four point bending of granite-shotcrete beam.The simulation results are in good agreement with the experimental results,which fully verifies the influence mechanism of the elastic modulus and compressive strength of granite and shotcrete on the deformation of composite structure,that is,the strength of shotcrete determines the ultimate bearing capacity of composite structure.The higher the elastic modulus of shotcrete and granite,the greater the deformation degree of composite structure,and the wider the crack caused by failure.At the same time,the fracture process of composite specimens is divided into three stages:elastic deformation,rapid crack of specimen,instability of fracture,and the crack propagation law of each stage.（4）Based on the diversion tunnel project of"Diverting from Songhua River into Changchun",this paper investigate the application of the D-DF-F model in engineering scale.The deep buried project is selected in the section of grade III surrounding rock and grade IV surrounding rock respectively.Based on the redistribution law of surrounding rock stress caused by deep tunnel excavation,the geometric size of the model and the range of discrete element subdomain are determined,calculated and applied the crustal stress.The unloading model of tunnel excavation is established by FLAC^3D and PFC^3D software,obtained the variation rules of radial stress field,tangential stress field and displacement field of surrounding rock.It is found that the deformation and damage of surrounding rock at the vault and intrado of tunnel are serious.By comparing the data of actual engineering and FLAC^3D numerical simulation,it shows the advantages of the D-DF-F model in the study of engineering scale rock mass problems.It can not only set discrete element particles in the large deformation and damage parts of rock mass,restore the characteristics of anisotropy and non-uniformity of rock mass,show the fracture,crack initiation and propagation of rock mass,but also reduce the number of discrete particles and ensure the calculation efficiency rate.The research results of this paper play a certain reference value in promoting the application of continuous-discrete coupling numerical simulation method in multi-scale study of deep tunnel deformation and damage.