Abstract: Model experiments are conducted on polymethyl methacrylate (PMMA) materials to investigate the influence of empty holes with different shapes on directional fracture controlled blasting of rock. A new digital laser dynamic caustics is applied to obtain caustics patterns around empty holes. Experimental results show that the preset rhombic hole can achieve fine directional fracture controlled blasting and effectively ensure the forming effect of blasting around the roadway. By comparing the propagation velocity of blast-induced cracks in specimens containing empty holes with three different shapes, it is found that the velocity of blast-induced main crack in a specimen with a rhombic hole is the greatest, then the velocity in a specimen with a circular hole is followed, and the velocity in a specimen with a circular hole with groove is the lowest. The values of dynamic stress intensity factor (DSIF) at the tips of blast-induced main cracks in specimens with a circular hole are generally higher than that in specimens with a rhombic hole and a circular hole with groove. The values of DSIF in specimens with rhombic holes are relatively low during the middle and late stages of blast-induced main cracks propagation.

Key words: empty hole, directed fracture controlled blasting, caustics, dynamic stress intensity factor