Abstract
Slotting blasting is widely used for directional fracture in geotechnical engineering. Due to limited research methods, the basic propagation theory of stress waves has not yet been applied in the literature to explain directional fracturing mechanism. In this work, the stress wave propagation during slotting blasting has been analyzed, and through the dynamic caustics blasting experiments, the blastings in circular-holed, square-holed and slotting-holed specimens have been contrast-analyzed, the propagation of stress waves and the explosion cracks have been observed. The theoretical and experimental results show that ① As the shock wave reached the slotting tip, based on “Huygens principle”, it separated into two independent waves symmetric to the median axis of the slotting tips and transmitted in different directions, due to directional stress concentration in materials. The directional fracture zone and directional damage zone were formed as the stress wave is attenuated during propagation; ② Observed in the experiment. The stress waves, which propagated outward in concentric circles, in circular-holed specimens did not change in form. Whereas those of square-holed and slotting-holed specimens changed significantly. The presence of the blasting hole tip changed the stress wave propagation form in the specimen, and the tip propagation angle of stress wave measured was in good agreement with the theoretical calculation; ③ The explosion cracks of the experiment specimens have been analyzed statistically. The blasting holes with tip overcame the static field stress, since the directional damage zone have been formed, leading to directional initiating and propagation of the cracks. In circular-holed specimens, the distribution of crack initiation was random, and in square-holed and slotting-holed specimens, the cracks were initiating at the tip. Crack deflected at twice blasting hole diameter and at six times blasting hole diameter in circular-holed and square-holed specimens, respectively. In contrast, cracks didn't deflect in slotting-holed specimens. The research results can provide theoretical support for selecting the shape and arrangement of the blasting holes for directional fracturing in geotechnical engineering.
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