Evolution characteristics of rockburst considering grain size and excavation unloading using 3D polycrystalline discrete element method

Based on the polycrystalline modelling system and basic theory of 3D discrete element, a 3D polycrystalline discrete element method (3DPDEM) that can indicate the microstructure of heterogeneous rocks was proposed to simulate the catastrophe process of rockburst. Interface program of NEPER-DEM data was developed to automatically output a simulation fine model of crystal scale (CSFM) for the consideration of mineral grain composition. The evolution characteristics of rockburst considering grain size and excavation under the condition of true triaxial with one-sided unloading was investigated. The findings show that the catastrophe process of rockburst in coarse-grained sample can be classified into: grain ejection, rock spalling into plate, rock shearing into fragment, and rock fragment ejection. The fine and medium grained sample have undergone processes such as small grain ejection, spalling, buckling, loosening, etc. The peak stress of coarse-grained sample is 28.19% and 10.05% higher than that of fine and medium-grained sample, respectively. The grain size has an important influence on the rockburst proneness, and the coarser the grain size, the stronger the rockburst proneness. The acoustic emission count of coarse-grained sample is 1.27 and 1.16 times higher than that of fine and medium-grained sample, respectively. The fine and medium-grained sample demonstrate rupture-loosening type rockburst, and the coarse-grained sample demonstrate burst-ejection type rockburst under the same loading and unloading path. The shape of rock slice (rock block) formed by the rockburst in the simulation (coarse-grained) and the actual engineering is similar, and the effect of CSFM the engineering scale problem is achieved.