Research On The Performance Of Hydraulic Slotting Technology Applied In Roof And Its Effect On The Gas Drainage

Recently coal requirement amount rises in a rapid rate with the high-speed economic growth of our country which leads to mining depth increasing year by year.Thereupon gas disaster is more serious day after day.In order to control gas disaster,hydraulic slotting has become a commonly used technical measure.However,the drilling fields generally are arranged in floor rather roof.Field test of hydraulic slotting in roof has not been carried on extensively.It is instructive to research and analyze the performance of hydraulic slotting technology applied in roof and its effect on the gas drainage.Concerning this issue,theoretical analysis,physical experiment,numerical simulation and field test have been taken to draw the main conclusions as follows.(1)According to drilling angle of borehole,high-pressure water jet could be divided into submerged and unsubmerged water jet which dynamic characteristic and morphology structure had been described during hydraulic slotting in roof.A mechanical differential equation which was verified by field test was established to explain blocking phenomenon in borehole when hydraulic slotting.And application condition of hydraulic slotting in roof was provided.(2)Physical experiment results shown that high-pressure water jet generated a slightly stronger disturbance in upward borehole than downward borehole under lowpressure dynamic load and a distinctly stronger disturbance in downward borehole than upward one under high-pressure dynamic load which was revealed by surface dynamic strain of samples.Broken characteristic of samples reflected that hydraulic cavitation promoted the fracture of samples under high-pressure dynamic load.To solve this problem,advancing broken zone was put forward to explain stronger disturbance existing in downward borehole during hydraulic slotting for the reason of cavitation.(3)Analysis of residual gas pressure in coal seam by numerical simulation discovered that a forceful coupling effect existed between boreholes in horizontal and vertical direction after hydraulic slotting.Gas drainage rate of single borehole was improved by reinforcement effect between slotting boreholes.Furthermore,it is the coupling effect between boreholes that should be considering to arrange drilling field more than the effective drainage radius of single borehole which avoided a waste of project amount.Compared gas drainage effect after hydraulic slotting in roof and floor,gas pressure relief and outburst elimination area was more uniform and connected in roof model.(4)Gas concentration and flow increased by hydraulic slotting in roof which indicated that field test received a satisfying consequence in gas pressure relief and permeability improvement in coal seam.The physical experiment and numerical simulation results was confirmed by data gathering in field test.It is meaningful to lay a theoretical foundation to guide hydraulic slotting applied in roof.