|Underground Coal Mining|
Underground mining techniques, which account for the majority of West Virginia’s coal production, utilize machinery to drive tunnels under the surface of the land. These tunnels are situated in coal seams so as the machinery advances further underground, coal is removed. Using a combined system of vehicle haulage and conveyor belts, the coal extracted from the seam is transported to the surface. Underground mining is practical from engineering and safety standpoint for coal seams that are located more than 100 feet below the surface of the land. Underground mining in shallower coal reserves will often encounter mine roof integrity problems as the geology and overburden at such shallow depths is less consolidated and more susceptible to cracking and failure (roof falls) than the strata above deeper coal seams.
Underground mines are usually characterized by the way the coal seam is accessed from the surface and the underground extraction method used to mine the coal. The method for accessing a coal seam for underground extraction is largely dependent on its vertical position relative to the surface. The three methods of underground mine access are summarized in Figure A.1.
Methods of Entry to Underground Coal MinesAn individual underground mine may have more than one of these access methods, depending on the characteristics of the individual coal seam, the coal haulage system used at the mine, the ventilation, roof control and safety plans for the mine and the mine’s supply and employee transport considerations. Underground mining coal extraction methods can generally be divided into two categories: room and pillar mines and longwall mines. The type of extraction practiced is dictated by the characteristics of the coal seam and its related geology. Generally, longwall mining is restricted to seams with uniform geology and coal seam thickness while room and pillar mining is more adaptable to seams with varying thickness, uniformity and geologic settings.