Creep Behavior and Associated Acoustic Characteristics of Heterogeneous Granite Containing a Single Pre-existing Flaw Using a Grain-Based Parallel-Bonded Stress Corrosion Model

Understanding the microcracking mechanisms and associated acoustic characteristics involved in the creep of heterogeneous granite at the grain scale is of high importance in practical engineering. To perform this task, a series of creep numerical simulations were conducted on granite with a single pre-existing open flaw using a grain-based parallel-bonded stress corrosion model. We investigated the effect of flaw inclination angle on the creep behavior and discussed the significance of microstructure. The results suggest that the axial strain, secondary creep strain rate and time-to-failure all depend strongly and nonlinearly on the flaw inclination angle. Creep failure is mainly induced by the initiation, propagation and coalescence of microcracks, and the dominant types are inter-grain tension cracks and intra-grain tension cracks. The b value, source types and distribution of acoustic emission events are associated with the flaw inclination angle and driving-stress ratio. Tensile sources account for the majority of the total number of acoustic emission sources, while shear and implosive acoustic emission sources are larger in magnitude. The model with higher heterogeneity creeps at a faster rate under the same applied constant axial stress. The higher number of acoustic emission events at each creep stage of such model indicates that the relatively heterogeneous microstructure provides more paths for the growth of microcracks during creep loading. As the heterogeneity increases, the secondary creep strain rate rises and the b value decreases. The position of the final macroscale shear band of pre-cracked granite is more affected by pre-existing flaw compared to its microstructure.