Study on the mechanism and field test of directional fracture blasting of iron mine tunnel surrounding

In order to study the applicability of directional fracture blasting technology with slotted cartridge in hard rock tunnel, the blasting effects of normal cartridge and slotted cartridge are compared by numerical simulation and field test of iron mine tunnel, and the field test results are quantitatively evaluated by using multifractal spectrum parameters.The test results show that the energy distribution of the slotted cartridge is more reasonable and the energy cumulative effect is obvious, which is conducive to crack penetration.In the field comparison test, the effect of slotted cartridge is better than that of the normal cartridge, and the rate of half-hole marks is more than 80%.After blasting with normal cartridge,the opening width of wall rock multifractal spectrum △α and dimension difference △f are 0.222 and 0.123, respectively, and after blasting with slotted cartridge,the △α and △f are 0.057 and 0.016, respectively.The value of the asymmetric index I_ASof multifractal spectrum is 0.774 and 0.122, respectively.The results show that the directional fracture effect of the surrounding blasting with the slotted cartridge is obvious and the surrounding rock surface is smoother and flatter.The directional fracture technique is also applicable to the hard rock tunnel such as the iron mine tunnel.