Abstract:

In order to optimize the rock-breaking effect of slit charge and control blasting to reduce rock disturbance, a blasting model test was carried out. The test was conducted to blast cylindrical red sandstone under the strip-shaped slit charge frame. The charge sections were set up in three positions: top, middle, and bottom along the axial direction of the air cylinder. After the blasting, CT technology was used, and the damage to the red sandstone after the blasting was quantitatively evaluated based on the fractal dimension theory. The results show that the blasting of the air-deck charge at the top and bottom in the middle of sample B exhibits the optimal controlled blasting effect. Its overall damage degree and porosity are the lowest, and the damage is more concentrated in the direction of the slit of the charge. The fracture morphology is approximately symmetrical, and the expansion is stable. In contrast, the other two both show different degrees of multi-fracture deflection. The analysis of segmented damage shows that the damage degree of the charge section is lower than that of the adjacent sections. The data image is approximately concave, which proves that the blasting energy has an attenuation effect and a local strengthening effect in the axial direction. The synergistic effect of the slit steel pipe and the air deck can effectively guide the blasting energy to be released smoothly along the slit direction, providing the possibility of achieving safe and low-consumption directional rock breaking.

Key words: air-deck charging, slit charge, blasting, computed tomography (CT), fractal dimension, damage