Abstract: Studying the meso-cracking evolution of rocks is of help to reveal the macro-cracking mechanism. Based on numerical simulations using block discrete element GBM (Grain Based Model), we proposed a method of calibrating mesoscopic parameters of the GBM rock specimens through analyzing the influence of inter-granular contact parameters on the rock macro-parameters under uniaxial compression tests and straight-pull tests. Using the present method, we further investigated into the evolution of transgranular cracks and grain-boundary cracks between different minerals of granite under uniaxial compression, and compared the numerical results with laboratory test results. Our findings revealed that the Poisson's ratio and elastic modulus of rock can be calibrated by using inter-granular contact stiffness, and the peak strength of rock can be calibrated by inter-granular tensile strength, cohesion and friction angle. The tensile strength of rock is affected most remarkably by the inter-granular contact tensile strength. The numerical simulation results of granite under uniaxial compression are consistent with laboratory tests: the number of transgranular cracks is significantly smaller than the number of grain-boundary cracks, and the quartz-biotite grain-boundary cracks are larger than feldspar-biotite grain-boundary cracks. In conclusion, the block discrete element GBM with improved calibration method can well simulate the behavior characteristics of grain-boundary cracks and transgranular cracks in rockmass as it considers the contact effect of bearing plate and the calibration of rock's peak strength.

Key words: rock mass, GBM, meso-parameters, calibration method, grain-boundary cracks, transgranular cracks