Damage Characteristics and Fracture Patterns of Sandstone Under the Coupled Effects of Blasting Stress and In Situ Stress

To investigate the influence of the in situ stress on the damage characteristics and fracture patterns of sandstone, this study designed a confining pressure loading device that simulates a deep high in situ stress environment. It allows for the coupled loading of blasting stress and in situ stress on rock specimens. Based on this, experimental research on three-dimensional rock blasting was conducted. A segmental analysis method was then applied, dividing the sandstone into stemming, charge, and bottom segments to refine the study. Using CT scanning, three-dimensional reconstruction, multifractal methods, and SEM scanning technology, the damage characteristics and failure modes of sandstone under the coupling of blasting stress and in situ stress were investigated from macroscopic, mesoscopic, and microscopic perspectives. The experimental research indicates that, under in situ stress, the rock’s ability to resist the effects of blasting stress waves and blasting gas is enhanced. With increasing in situ stress, the overall damage level of sandstone specimens gradually decreases and the damage characteristics in different segments of the specimen show significant variation. Under the same in situ stress, the damage level of the sandstone specimen decreases as the axial position shifts from the stemming segment to the charge segment, and then to the bottom segment. Additionally, with increasing in situ stress, shear fractures increase, the blasting fracture surfaces become progressively rougher, and the microscopic fractures in the sandstone transition from brittle cleavage fractures to brittle–plastic quasi-cleavage fractures. In some areas, the energy is insufficient to penetrate the grain boundaries, leading to a transition from transgranular fractures to coupled fractures and intergranular fractures.