Experimental study of propagation of directional fracture with slotting hydraulic blasting

In conventional deep-hole pre-splitting blasting to enhance the permeability of low pervious thin coal seam in Southwest China,roof collapse and floor heave usually occurs fracture propagates disorderly in blasting. To maintain the integrity of roof and floor at gateroad,a slotting-hydraulic blasting technology was proposed utilizing the fracture guidance of groove blasting and the efficiency of hydraulic blasting. Fracture initiation and stress evolution with cou- pling charge blasting,slotting air uncoupling charge blasting and slotting-hydraulic blasting techniques were experi- mentally studied. The results show that the slotting-hydraulic blasting can create two dimensional fracturesin large area along expected direction. With the same dose of explosive,exposure area is 1. 42 times and 11 times of that with slot- ting air uncoupling charge blasting and coupling blasting,respectively. Also,the peak stress of explosion is higher than that of slotting air uncoupling charging,up to 1. 5 times. It is also found that larger stress variation occurrs in the apical direction when using slot hydraulic blasting by comparing with the other two methods. This indicates that slot hydraulic blasting can lead to more violent particle vibration which is good for fracture initiation and propagation,and hence can be better for roof and floor integrity.