what are the different types of coal mines
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Room and Pillar Mining This drawing depicts the room and pillar method of underground mining. Most underground coal is mined by the room and pillar method, whereby rooms are cut into the coal bed leaving a series of pillars, or columns of coal, to help support the mine roof and control the flow of air. Generally, rooms are 20-30 feet wide and the pillars up to 100 feet wide. As mining advances, a grid-like pattern of rooms and pillars is formed. Workers drive bolts of up to eight feet long in the roof of the rooms to keep the rock above the coal seam from falling in. When mining advances to the end of a panel or the property line, retreat mining begins. In retreat mining, the workers mine as much coal as possible from the remaining pillars until the roof falls in. When retreat mining is completed, the mined area is abandoned.
There are two types of room and pillar mining — conventional mining and continuous mining. Conventional mining is the oldest method. In conventional mining, the coal seam is cut, drilled, blasted and then loaded into cars. Continuous mining is the most prevalent form of underground mining. In continuous mining, a machine known as a continuous miner cuts the coal from the mining face, obviating the need for drilling and blasting.
Longwall Mining This drawing depicts the longwall method of underground mining. Longwall mining now accounts for about 31% of underground coal production. There are over 100 longwall operations in the United States, most of them in mines in Appalachia. In longwall mining, a cutting head moves back and forth across a panel of coal about 800 feet in width and up to 7,000 feet in length. The cut coal falls onto a flexible conveyor for removal. Longwall mining is done under hydraulic roof supports (shields) that are advanced as the seam is cut. The roof in the mined out areas falls as the shields advance.
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Room and pillar mining
Long wall mining
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