Experimental study on reciprocating hydraulic slotting technology and its slotting performance

To address the issues of shallow slotting depth and poor permeability enhancement effect in hydraulic slotting of hard coal in coal mines, a reciprocating hydraulic slotting technique is proposed. This technique uses a dynamic impact load to weaken the water cushion effect and improve slotting performance. Based on a comparative analysis of the working principles and coal-breaking characteristics of conventional hydraulic slotting and reciprocating hydraulic slotting, numerical simulations of high-pressure water jet impacting coal and hydraulic slotting experiments were conducted to investigate the slotting performance of the reciprocating technique and its main influencing factors. The results show that the formation time of the water cushion during jet coal-breaking ranges from 60 μs to 120 μs. The thickness and radius of the water cushion increase initially and then stabilize over time, reaching stable values of 5.6 mm and 7.6 mm, respectively. Under the same jet pressure and impact time, the maximum slotting depth achieved by reciprocating hydraulic slotting is 1.51 to 2.01 times that of conventional hydraulic slotting. The slotting depth of the reciprocating technique increases with increasing jet pressure and slotting time, but an upper limit exists.