Modelling micro-cracking behaviour of pre-cracked granite using grain-based distinct element model

Abstract

In this paper, the micro-cracking behaviour of pre-cracked Barre granite is investigated using a grain-based distinct element model (GBM). We investigated and demonstrated a cohesive model in a distinct element code, PFC2D, to mimic the elastic and softening response of the intra-grain contacts in the GBM. The study employed the smooth-joint model to simulate the micro-cracking behaviour of grain interfaces. The grain size distribution, as well as the mineral constituent of Barre granite, was incorporated in the numerical model. The model was calibrated against uniaxial compressive strength and Brazilian split-tensile-strength tests. We found that the GBM framework successfully reproduced the macroscopic physical properties obtained from the laboratory tests. When calibration was complete, the geometries of pre-existing cracks, which were considered in the experimental testing, were imported into the numerical model and used to generate synthetic, pre-cracked Barre granite. The macroscopic cracking process in the generated numerical models was observed by monitoring the evolution of intra- and inter-granular micro-cracks. The cracking and coalescence behaviour of numerical pre-cracked granite revealed that the proposed GBM approach can replicate the macroscopic fracturing pattern of pre-cracked Barre granite with close agreement to the experimental observations. The crack initiation, coalescence, and peak axial stresses were also recorded during numerical testings, and a good agreement was also achieved between these simulated results and the laboratory data. The proposed GBM framework is promising for research into micro-cracking behaviour of pre-cracked crystalline rocks under compressive loading.