## 4 Analysis of Rock Fracture Patterns
### Microscopic Analysis of Blasting Fracture Modes
In the charge segment, compared to the stemming segment, dimple patterns gradually increased, indicating a transition from brittle to brittle-plastic fractures, with a significant increase in the intergranular and coupled fractures. Additionally, under the same in situ stress condition, as the position shifted from the stemming segment to the charge segment, and then to the bottom segment, the fracture mechanism remained primarily dominated by tensile stress, but the proportion of shear stress influence gradually increased. The deformation form of the fracture, predominantly brittle cleavage, gradually transitioned to brittle-plastic quasi-cleavage fracture. The fracture path, mainly transgranular, was progressively replaced by intergranular and coupled fractures. In the absence of in situ stress, the stemming segment accumulated and released blasting energy quickly, causing rapid tensile stress at high strain rates that fractured the rock along the micro-voids, resulting in smooth tensile fracture surfaces. This made the stemming segment's fracture morphology predominantly tensile and brittle cleavage, with shear fractures and brittle-plastic quasi-cleavage fractures rarely observed. Under in situ stress, part of the blasting energy was used to counteract the constraint effect of the in situ stress, resulting in reduced stress peaks and strain rates. Consequently, in the stemming segment under 0.5 MPa in situ stress, the fracture morphology showed not only tensile and brittle cleavage fractures but also a small amount of shear and brittle-plastic quasi-cleavage fractures. With increasing in situ stress, the stress peaks and strain rates further decreased, leading to more shear and brittle-plastic quasi-cleavage fractures. Furthermore, as the in situ stress increased, the blasting energy available for rock fracturing gradually decreased, resulting in an increase in coupled fractures and intergranular fractures in the plugged section starting at an in situ stress of 1 MPa. Similarly, the charge segment already showed a small amount of shear and brittle-plastic quasi-cleavage fractures without in situ stress, and, as the in situ stress increased, the occurrence of these fracture types became more prevalent. Coupled fractures began to appear in the charge segment under 0.5 MPa in situ stress, and intergranular fractures appeared under 1 MPa in situ stress, with both types becoming more common as the in situ stress increased. In the bottom segment, the blasting energy available for rock fracturing had decreased to a certain level, leading to the appearance of a small amount of shear, brittle-plastic quasi-cleavage, and coupled fractures even without in situ stress. Intergranular fractures started appearing at 0.5 MPa in situ stress. At the same location, no fractures were observed under the 1 MPa and 2 MPa in situ stress conditions. As the in situ stress increased, the blasting energy available for rock fracturing decreased, resulting in a lower peak blasting stress and strain rate. This led to fracture morphologies influenced by both tensile and shear stress, producing increasingly rough fracture surfaces and brittle-plastic quasi-cleavage fractures. In some areas, the insufficient energy to penetrate grain boundaries resulted in coupled and intergranular fractures. As the position shifted from the stemming segment to the charge segment, and then to the bottom segment, the diminishing blasting energy caused the microfractures in the rock to become increasingly rough and disordered, leading to more irregular fracture surfaces.