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

Abstract

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 is established, which can simultaneously reflect the structure and content of mineral granules in rock. To verify the applicability and reliability of the ECM to further study the macroscopic nonlinear mechanical behaviour and fracture mechanism of rocks from a mesoscale perspective, this paper carried out numerical simulations of direct tension, uniaxial compression and triaxial compression loading using the particle flow code software, and the numerical results were compared with the test results of Beishan granite. The main research results are summarized as follows. (1) Under the condition of triaxial compression, with the increase in the confining pressure, the axial peak strain, radial peak strain, volume peak strain and post-peak residual strain of the rock all show an increasing trend. The rock exhibits an axial splitting failure mode dominated by 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 the middle of the specimen and extending approximately perpendicular to the tensile load direction, forming an approximately horizontal macroscopic crack composed of mineral granular boundaries. (3) The use of the ECM can reproduce a high ratio of the uniaxial compressive strength to the uniaxial tensile strength of the rock, and its strength characteristics show obvious nonlinear characteristics and meet the Hoek–Brown strength criterion. The rock strength and failure type obtained from the simulation are basically consistent with the test results, demonstrating the reliability of the ECM.