Experimental Study on Quasi-Static Pressure of Slot Hydraulic Blasting

Air is commonly used as the noncoupling borehole medium in directional slot blasting where the quasi-static pressure is small, the energy utilization rate of the explosive is low, and the breaking efficiency of the coal-rock mass is not high. This study investigates the effect of quasi-static pressure on crack propagation in closed-field blasting. Crack length propagation in the quasi-static pressure stage accounts for more than 60% of the total crack length. Water is therefore proposed as the noncoupling medium of the slotting borehole to increase the quasi-static pressure. A series of experiments was performed to investigate and compare quasi-static pressures generated using noncoupled water-medium blasting and noncoupled air-medium blasting. The experimental results show that the quasi-static pressure is 37-46 times larger in water-medium blasting than in the air-medium case. The experimental measurements show good agreement with theoretical analysis. The results show that the energy utilization rate of the explosives in the hydraulic slotting blasting is high with a notable energy storage effect, and that the fracturing range can be significantly increased. Additionally, fracture by directional blasting using this approach can be more controllable.