Directional Fracture Blasting Using Slit Charges and Its CT-Based Transverse Damage Characteristics

Based on blasting principles, laboratory tests with different blasting parameters were conducted on rectangular prism granite specimens containing a single borehole. The effects of stemming condition, charge structure, charge mass, and decoupling coefficient were investigated. The results showed that slit charges and borehole-end stemming both improved blasting performance, and their combined use produced a better effect. The decoupling coefficient strongly affected the initiation, propagation, and distribution of blast-induced cracks. Rather better directional fracture-blasting performance was obtained at a decoupling coefficient of 1.67. Increasing the charge mass alone did not necessarily improve the blasting effect. CT scanning was further used to observe and characterize damage in the blasted specimens. Transverse damage decreased gradually with the increase in borehole depth. The box-counting fractal dimension also decreased along the borehole depth, indicating a reduction in fracture complexity. It should be noted that CT scanning characterizes transverse damage in the scanning direction only and cannot directly describe damage along the borehole axis. More fundamentally, blast-induced rock damage results from the coupling between the dynamic response under explosive loading and the structural effects associated with the physical and geometrical characteristics of the rock.