Influence of initial micro-crack damage on strength and micro-cracking behavior of an intrusive crystalline rock

Rocks inherently contain some micro-cracks. The existence of initial micro-cracks introduces weakness to the rock specimen and hence affects the strength and deformation behavior of rocks. This paper numerically investigates the influence of initial micro-crack damage on the strength and deformation behavior and the associated micro-cracking process of a crystalline rock using a previously-calibrated grain-based model (GBM), which is implemented in two-dimensional Particle Flow Code (PFC2D). The initial micro-crack damage is generated by loading/unloading of the model numerically, and a damage parameter is defined to quantify the degree of initial micro-crack damage. After the initial micro-crack damage is generated, compressive loading tests under different confining pressures are conducted. The simulation results reveal that the initial micro-crack damage has a significant influence on the simulated stress–strain curve, rock strength, elastic modulus, and total number of generated micro-cracks. In general, as the initial micro-crack damage increases in the numerical model, the simulated rock strength and elastic modulus gradually decrease. However, the decrease in rock property (strength and elastic modulus) will become significant only after sufficiently high initial micro-crack damage in the model is reached. The elastic modulus to UCS ratio (E/UCS) is not significantly affected by the initial micro-crack damage. Overall, the initial micro-crack damage weakens the model. The simulation results are in good agreement with previous laboratory tests results. The PFC2D-GBM approach in this study can be used to capture the strength and deformation behavior of damaged rocks, which are induced from initially-generated micro-cracks, e.g., rock drilling and coring, cyclic loading, and thermal loading.