Cracking behavior and acoustic emission characteristics of heterogeneous granite with double pre-existing filled flaws and a circular hole under uniaxial compression: Insights from grain-based discrete element method modeling

In geological engineering, the existence of fault fracture zones has an obvious impact on the stability and failure process of the surrounding rock of mountain tunnels. In this study, a series of models with double pre-existing filled flaws and a circular hole were established and simulated under uniaxial compression. The results indicate that the existence of filled flaws and hole degrades the mechanical properties in the model. Specifically, as the distance of double filled flaws decreases and their inclination angle increases, the Young's modulus and uniaxial compression strength decline. When the inclination of the double pre-existing filled flaws is close to the rupture angle of the intact model, the mechanical properties of the model are the smallest. In addition, microcracks mainly initiate at the filled flaws and the left and right sides of circular hole. Most of the microcracks are tensile cracks, and only little shear microcracks are developed. It is also found that the source types of the acoustic emission events and b-value are related to the position and inclination angle of filled flaws. The source types of events that make up the shear band may be mainly tensile or shear. Implosive and shear events also significantly contribute to macroscopic failure. In addition, the b-values display a negative correlation with the increasing distance of double pre-existing filled flaws. The above results show that the stability of mountain tunnels may be evaluated by analyzing the position and inclination angle of fault fracture zones in tunnel engineering.