Distribution Laws of Crossing Boreholes Plastic Zone in Coal Seam Gas Drainage

Applying FLAC^3D software, combining with Tecplot software image processing functions, by doing slices in different distance from the intersection, the distribution laws of plastic zone near the crossing boreholes intersection was studied. Researches show that when crossing boreholes pumps the coal seam gas, the plastic zone of crossing boreholes intersects under certain conditions. Plastic zone intersects generally only in a certain distance away from the intersection point, and with increasing distance from the crossing point will disjoint. The size of elevation difference and intersection angle between crossing boreholes impacts the size of crossing zone. The size of crossing zone decreases with increasing elevation difference, and decreases with increasing intersection angle. For Jiulishan Mine 244 m depth of coal seam, crossing boreholes elevation difference is suggested less than 6 times of the hole diameter.