Method and Technology of Green Coal Mining

residual coal pillar; gob-side entry driving; extra-thick coal seam; coal pillar size; surrounding rock control; directional long borehole; long-distance; heading face; permeability evolution; gas pressure evolution; gas drainage; pre-splitting blasting; roof cutting technology; hydraulic fracturing; no-coal pillar mining; thick hard roof; pressure relief technology; sandstone; deformation behavior; permeability evolution; mining stress path