Strain rockburst evolution process under true triaxial condition with single face unloading due to tunnel excavation

Based on the technology of polycrystalline modelling (generating Voronoi polycrystal) and three-dimensional discrete element theory, a three-dimensional polycrystalline discrete element nonlinear dynamic and static coupled numerical analysis method was proposed. This method can accurately simulate the initiation and evolution entire process of strain rockburst. The three-dimensional Voronoi polycrystalline discrete element model considering the mineral composition was established. The rockburst simulation of heterogeneous granite under true triaxial single face unloading was carried out. The rockburst ejection failure characteristics, strength and deformation characteristics, acoustic emission characteristics of rock samples were analyzed, as well as the characteristics of rock fragments and the evolution law of kinetic energy. The inoculation and evolution entire process of strain rockburst during true triaxial single face unloading was studied. The research results show that the failure process of rockburst ejection can be divided into four stages, including: grains ejection, rock spalling into plates, rock shearing into fragments, and rock fragments ejection. The failure modes of rockburst are pluralistic, that is, rockburst pits caused by tension-shear failure and split cracks due to tensile failure near the unloading face, and shear cracks caused by shear failure away from the unloading face. The kinetic energy is released abruptly in the post-peak stage, and the kinetic energy suddenly increases from zero to a high value when elastic energy drops sharply. The dissipation energy of rockburst fragments mainly includes shear dissipation energy and tension dissipation energy; among them, the shear dissipation energy accounts for 99.66 %. The primary conditions for rockburst ejection failure are accumulating enough elastic strain energy and reaching a large loading rate in the tangential direction.