Research On Drilling Long Hole In Soft Coal Seam By High Pressure Water Jets

The existing drilling technology is so frequently affected by coal seam geological condition in mine that the drill easily collapses and limits the length of the hole in a short scale, which impairs gas drainage and the safety of the mine. Referring to Science Fund for Creative Research Groups (50621403), a series of experiments related to coal drilling by high pressure water jets(HPWJ) were carried out. The influence of parameters of HPWJ on drilling effect was analyzed. What's more, the coal's damage is scanned by CT scan device and the results shows that the edge of the coal is lossless. Based on the two experiments, the model of the HPWJ drilling for the long hole is built. Compared to the existing drilling, the displacement change and stress distribution of HPWJ drilling is analyzed respectively. Finally, the results on theoretical analysis were verified by field experiment in Chongqing Mine.The main contents and conclusion are as follows:①The experiment of the coal strength shows that the average of the maximum uniaxial compressive strength, elastic modulus and poisson ratio is 2.01MPa, 0.061Gpa and 0.22, respectively.②The experimental results of HPWJ shows that the relation between punching depth and pump pressure is conic, the relation between punching depth and target distance is cubic. The impact load and the quasi-static pressure of the HPWJ coactions in the process of drilling, the impact load is significant important.③The CT scan shows that the coal doesn't have significant crack by HPWJ drilling and the damage of coal is not obvious. Coal impairment around the holes was small.④The comparative two-dimensional model about HPWJ drilling and existing drilling technology is built respectively. Besides, for HPWJ the three-dimensional is built. It can be concluded that the displacement of the hole drilled by HPWJ changes more slowly than that by existing drilling technology as the time steps increasing. When the length gets longer, the coal's end effect is more significant; the HPWJ supports the hole and enable it longer.⑤Using HPWJ drilling in a mine of Chongqing, it gets 147m, also the average length and drilling velocity is 2~3 and 1.6 times of the existing holes, respectively, which coincide the calculated results.