Critical Parameters Of High Pressure Water Jet Slotting In Coal Seam

China itself is one of the worst coal and gas outburst disaster-prone countries in theworld, and the proportion of outburst in coal mine disasters is rising with the increasingof coal production. To solve the problem, many kinds of ways have been studied. Highpressure water jet slotting in coal seam is one of the fewest methods that can dischargegas in coal seam efficiently and prevent outburst, and it’s widely used in outburst coalmine. In this case, further analysis and research was done to perfect its theory, andpromote its standard application in coal mine. The main research results are as follows.①According to the main mechanism of coal broken with high pressure water jet,theory of cutting rocks by Crow, and field condition, the critical parameters thatinfluence the depth of slotting in coal seam mainly include jet pressure, nozzle diameter,rotate speed and slotting time.②A model was built to describe relationship between slotting depth and jetpressure, rotate speed and slotting time, when the nozzle diameter was fixed. FLUENTsimulation results showed that, the reasonable nozzle diameter should be3mm, for itsattenuation coefficient of axis dynamic pressure was the minimum. The experimentproved that the relationship between depth and jet pressure was in good linear whenwater jet was in free condition. The other experiment showed that both rotate speed andslotting time had a power correlation with slotting depth. Through calculation andanalysis, the optimal parameters of slotting coal should be: p=25MPa, d=3mm, t=0~5min, n=60r/min; t=5~10min, n=50r/min; t=10~15min, n=40r/min.③Site test showed that, the depth of high pressure water jet slotting in coal seamreached1.5m, which was matched with calculated value. Through optimization of thedrilling parameters, a field application was carried out in G15-12050wood road inPingBao Ltd., and the results showed that the number of drilling reduced44.4%, timeof crossheading shortened35.9%.