Microscale Characterization of Fracture Growth in Increasingly Jointed Rock Samples

Discrete element method (DEM) is employed to investigate the fracture growth and failure mechanism of increasingly jointed rock samples subjected to increasing confinements. Synthetic rock mass models are developed on the basis of joint configurations created within laboratory samples, and the micromechanical parameters of the DEM are calibrated to replicate the mechanical response measured in the laboratory. Subsequently, the effects of increasing the level of initial joint frequency and confining pressure on the strength, deformability, stress-strain relationship, and failure mode transition of the rock samples are analyzed. At the microscopic scale the tensile and shear crack distributions, fragmentation characteristics, AE frequency-magnitude statistics and spatial clustering of source locations are examined to shed light on the mechanical behavior and deformability of jointed rock mass. Results show that the distribution of the magnitude of AE events is prone to decay as power law in tandem with the spatial distribution of the source locations that exhibit a fractal character. Noteworthy is the decrease of seismic b values associated with failure pattern from axial splitting to shear fracture upon increase in confining pressure, which is indicative of an accelerating number of events of increased magnitudes. Finally, the microscopic evolution of the fabric and force anisotropy as well as the characteristics of spatial distribution of contact forces provide micromechanical insights into the macroscopic behavior of jointed rock samples upon the rise in confining pressure.