Fracture Behavior and Damage Mechanism of Red Sandstone under Loading: An Experimental and DEM Study

It is of paramount importance to investigate the fracture behavior and damage mechanism processes of red sandstone in order to elucidate the mechanisms underlying rock mass fracturing and slope deformation. Utilizing both experimental methods and discrete element modeling (DEM) using the Particle Flow Code (PFC), this study analyzes the impact of fracture angle on the mechanical deterioration behavior and damage modes of sandstone from a macroscopic perspective. Additionally, it explores stress evolution and damage processes in fractured sandstone at a finer scale, while examining fracture morphology and displacement vector characteristics at a microscopic level. The findings indicate that as the inclination of fractures increases, both peak strength and modulus of elasticity exhibit an upward trend. In intact rock, failure primarily occurs through tensile damage; conversely, fractured rock predominantly experiences tensile-shear composite damage. The results obtained from numerical simulations align closely with those derived from the experiments. The evolution of cracks during the process of destruction has a stage-specific feature and mainly generates tensile cracks. For intact rock, stress concentration occurs at both the upper and lower boundaries. In contrast, for fractured rock, stress is mainly concentrated at either end of the fissure before extending toward its boundary. A model for calculating the damage coefficient has been proposed by integrating acoustic emission data with energy loss principles. This model delineates three distinct stages in the rock damage process: the initial damage stage, the accumulation stage of damage, and the strengthening stage postdamage. The fracture mode of sandstone is primarily characterized by transgranular fractures (TG), with intergranular fractures (IG) also being present. The morphology exhibits features of tensile fractures, shear fractures, and mixed tensile-shear fractures. On the macroscopic shear surface of both intact and defective rock samples, the displacement direction of particles aligns parallel to the principal stress direction, predominantly resulting in tensile damage. It can be concluded that there exists a correlation among the macroscale, fine-scale, and microscale damage.