Underground Coal Mining.

                                                          
Underground Coal Mining. 

There are 5 types/ways of underground coal mining. 

1: Drift Mining.

Drift Mining is possible where the coal seam intersects the surface. The mine enters the seam in a horizontal direction following the coal. A drift may or may not intersect the ground surface. This kind of mining is done when the rock or mineral is on the side of a hill. The advantages is drift mining is much cheaper and much safer. Drift mining also has vertical access shafts. It is also much easier to transport ore out of the mine itself. Some disadvantages include the possibility of flooding. You can drain a drift mine with water, and still work as long as the adit is not blocked. 

2. Shaft Mining.

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Shaft Mining is the most common method accessing a coal seam in which elevators provide access to mines. Shaft coal mines in West Virginia are commonly deeper than 1,000 ft below the surface. (Also deepest form of underground mining.) Coal, gold, and copper are commonly mined in this form. When the ore is dynamited and broken into chunks, it is then put on a type of pulley system to be loaded into trucks. Much faster and conventional, would be an advantage. Also, moving air ventilates the gases that are naturally underground, for safer breathing. A disadvantage to this is tunnels are deepened and the mine is made larger until there isn't any ore left, or it costs too much money to get it out. Most shaft mines are filled and blocked with cement to prevent the land around it from sinking and rotting away. It's the safer way to close a mine. 

3. Room & Pillar Mining. 
Nearly half the coal is left behind to support the mine roof. The pillars can "squeeze" putting pressure on adjacent pillars leading to the to collapse. Roof falls are a constant danger. It is used to mine coal, iron, metal substances, soda ash, and potash. Disadvantages include a lot of mining/work, to have not a lot to come out with. The pillars help hold the roof up, yet can easily fall none the less. Advantages is it can be much faster than some mining. The pillars are removed or pulled to the front of the mine, to let it collapse behind to close it. 

4: Continuous Mining.
Machines can be used with drift or room & pillar mines. One miner can operate a continuous miner to a rotating steel drum with tungsten carbide teeth to mine 5 tons of coal per minute. Varieties of continuous mining machines have been in use since the 1940's. Advantages are it produces the lowest cost per ton a customer. Continuous mining accounts for about 45% of the underground mining. Disadvantages are not a lot of roof support. It's slowly become one of the more efficient way to mine.




5: Longwall Mining.

Highly efficient. Huge mining machines support the roof with hydraulics as it removes the coal. Once the coal is removed, the machine retreats allowing the roof to fall behind it. It extracts much more of the coal than the room & pillar mining techniques. Advantages include better resource recovery, fewer roof support, the miners' safety is better when they are extracting coal. Some disadvantages are, when the mining is done, and the hydraulics are taken away, the roof collapses, and could have a very severe, damaging impact of rivers and foundations of building. 

Hyperlink to access more knowledge.

Picture credits go to:
 (Drift Mining) en.wikipedia.org
 (Shaft Mining) dogcanyon.org
 (Room & Pillar Mining) mitchellpays.com
 (Continuous Mining) ohiovalleycoal.com
 (Longwall Mining) coalleader.com