Study On The Mechanical Properties And Damage Evolution Mechanism Of Marble Under Static And Dynamic Loading

In engineering applications,the rock mass is in a complex stress state.In the process of deep cavern excavation,stress redistribution is caused,resulting in new cracks inside the rock mass and crack-to-crack extension penetration,which will eventually cause destabilization of the rock mass.Therefore,it is important to study the mechanical properties,crack expansion and energy evolution of rocks under complex stress state.In this paper,based on the indoor conventional triaxial compression test results and dynamic splitting test results of marble,two numerical simulation techniques,discrete element and finite element,are combined to extend the study.The main contents and main conclusions are as follows:First,a conventional triaxial compression simulation was carried out by using the particle flow code to explore the internal relationship between the initiation and propagation of marble microcracks,damage evolution and energy conversion under different confining pressures.It is shown that the expansion of cracks in the rock sample during the compression process can be divided into four stages.The number of microcracks and damage variables satisfy the logistic function relationship with the axial strain.the energy value obtained from theory and simulation varies with the axial strain.The energy values obtained from the theory and the simulation showed the same trend with axial strain,and the evolution stages of each energy corresponded well with the crack expansion process.The maximum input energy density and the maximum dissipation energy density increase exponentially with the increase of the surrounding pressure,while the limit of energy storage density increases linearly with the residual elastic strain energy density.Then,true triaxial compression simulations of complete specimens were carried out to investigate the deformation and failure process,microcrack evolution mechanism and intermediate principal stress effect of marble specimens under different stress paths.The results show that the effect of intermediate principal stress on the peak strength,elastic modulus,failure angle and failure mode evolution is significant.The octahedral theory can be a good fit for the failure stress in true triaxial compression.Crack expansion during compression can be similarly divided into four stages.As the intermediate principal stress increases,the brittle failure characteristics of the post-peak section of the stress-strain curve become stronger,the specimen transforms from tensile failure to tensile-shear mixed failure,and the evolution of rock damage takes on a spoon-shaped trend as the （?）₂changes.Next,true triaxial compression simulations of the specimens with defects were carried out to investigate the effects of rock bridge dip angle and fissure length on the energy characteristics,crack evolution and failure mode of the marble specimens.The results show that the crack expansion pattern can be divided into three forms,but the larger the initial confining pressure,the more dispersed the crack distribution in the specimens.The effects of rock bridge dip and fissure length on the elastic modulus are not affected by the stress path,and the effect of confining pressure is greater than the effect of defects inside the rock.The effect of fissure length on the bearing capacity of the defected marble is greater than that of the rock bridge inclination,and the relationship between the maximum principal stress and the intermediate principal stress in the defected specimen at the constant minimum principal stress level is consistent with that of the intact specimen.Finally,dynamic splitting tests were carried out on the Jinping marble at three bullet velocities,and numerical simulations were performed according to the experimental results.The results show that the failure mode of dynamic splitting of marble is closely related to the bullet velocity of impact bullets,and the damage under low bullet velocity is consistent with static Brazilian splitting experiments,while the triangular crushing zone at both ends of the specimen becomes larger under high bullet velocity.According to theoretical calculation,empirical formula and concrete model parameters,34 RHT model parameters are finally determined.By comparing the experimental and simulated damage forms,it is found that the RHT model could better restore the fragmentation process of the specimen,but the average damage area percentage of the test is smaller than that of the simulated results.