Underground mining (soft rock)
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2008-05-11T13:45:28Z
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'''Underground mining (soft rock)''' refers to a group of underground mining techniques used to extract [[coal]], [[oil shale]] and other [[minerals]] or geological materials from sedimentary ("soft") rocks. Because deposits in sedimentary rocks are commonly layered and relatively less hard, the mining methods used differ from those used to mine deposits in [[igneous]] or [[metamorphic rocks]] (''see [[Underground mining (hard rock)]]''). Underground mining techniques also differ greatly from those of [[surface mining]].
==Methods==
* '''[[Longwall mining]]''': Longwall mining machines consist of multiple coal shearers mounted on a series of self-advancing hydraulic ceiling supports. Almost the entire process can be automated. Longwall mining machines are about 800 feet (240 meters) in width and 5 to 10 feet (1.5 to 3 meters) tall. Longwall miners extract "panels" - rectangular blocks of coal as wide as the mining machinery and as long as 12,000 feet (3,650 meters). Massive shearers cut coal from a wall face, which falls onto a [[conveyor belt]] for removal. As a longwall miner advances along a panel, the roof behind the miner's path is allowed to collapse.
* [[Room and pillar|'''Room-and-pillar mining''']] or '''continuous mining''': Room and pillar mining is commonly done in flat or gently dipping bedded ores. Pillars are left in place in a regular pattern while the rooms are mined out. In many room and pillar mines, the pillars are taken out, starting at the farthest point from the mine haulage exit, [[Retreat mining|retreating]], and letting the roof come down upon the floor. Room and pillar methods are well adapted to mechanization, and are used in deposits such as [[coal]], [[potash]], [[phosphate]], [[salt]], [[oil shale]], and bedded [[uranium]] [[ore]]s.
* '''[[Blast mining]]''' – An older practice of coal mining that uses explosives such as [[dynamite]] to break up the coal seam, after which the coal is gathered and loaded onto shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with "cutting" the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5% of total underground production in the U.S. today.
* '''[[Shortwall mining]]'''– A coal mining method that accounts for less than 1% of deep coal production, shortwall involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, depending on other things like the strata of the Earth and the transverse waves.
==See also==
*[[Mining]]
*[[Retreat mining]]
==External links==
*[http://www.post-gazette.com/downloads/20031123st_Mining.pdf Longwall technique]
{{Mining techniques}}
[[Category:Sub-surface mining]]
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