Mesoscopic Analysis of the Mechanical Properties of Beishan Granite Based on the Equivalent Crystal Model

摘要

The internal microstructure of rock has an important influence on its macroscopic mechanical properties and fracture mechanism.In this paper, an equivalent crystal model (ECM) consisting of a bonded particle model and smooth joint model isestablished, which can simultaneously reflect the structure and content of mineral granules in rock. To verify the applicabilityand reliability of the ECM to further study the macroscopic nonlinear mechanical behaviour and fracture mechanism ofrocks from a mesoscale perspective, this paper carried out numerical simulations of direct tension, uniaxial compressionand triaxial compression loading using the particle flow code software, and the numerical results were compared with thetest results of Beishan granite. The main research results are summarized as follows. (1) Under the condition of triaxialcompression, with the increase in the confining pressure, the axial peak strain, radial peak strain, volume peak strain andpost-peak residual strain of the rock all show an increasing trend. The rock exhibits an axial splitting failure mode dominatedby tensile cracks and gradually changes to a shear failure mode dominated by shear cracks at an angle of approximately 45°from the loading direction. (2) Under direct tensile conditions, the failure of the rock manifests as cracks initiating from themiddle of the specimen and extending approximately perpendicular to the tensile load direction, forming an approximatelyhorizontal macroscopic crack composed of mineral granular boundaries. (3) The use of the ECM can reproduce a high ratioof the uniaxial compressive strength to the uniaxial tensile strength of the rock, and its strength characteristics show obviousnonlinear characteristics and meet the Hoek–Brown strength criterion. The rock strength and failure type obtained from thesimulation are basically consistent with the test results, demonstrating the reliability of the ECM.