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Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice (typically 0.6 – 1.0 m thick). The longwall ''panel'' (the block of coal that is being mined) is typically 3 – 4 km long and 250 – 400 m wide. ==History== The basic idea of longwall mining was developed in England in the late 17th century. Miners would undercut the coal along the width of the coal face, removing coal as it fell, and using wooden props to control the fall of the roof behind the face. This was known as the ''Shropshire method'' of mining.〔(Longwall Mining ), Office of Coal, Nuclear, Electric and Alternate Fuels, U.S. Department of Energy, March 1995, pages 9–10.〕 While the technology has changed considerably, the basic idea remains the same, to remove essentially all of the coal from a broad coal face and allow the roof and overlying rock to collapse into the void behind, while maintaining a safe working space along the face for the miners. Starting around 1900, mechanization was applied to this method. By 1940, some referred to longwall mining as "the conveyor method" of mining, after the most prominent piece of machinery involved.〔A. Paxton, J. A. Biggs, (Ten Minutes in a Coal Mine ), 1940, Pages 16-24〕 Unlike earlier longwall mining, the use of a conveyor belt parallel to the coal face forced the face to be developed along a straight line. The only other machinery used was an electric cutter to undercut the coal face and electric drills for blasting to drop the face. Once dropped, manual labor was used to load coal onto the conveyor parallel to the face and to place wooden roof props to control the fall of the roof. Such low-technology longwall mines continued in operation into the 1970s. The best known example was the New Gladstone Mine near Centerville, Iowa "one of the last advancing longwall mines in the United States". This longwall mine did not even use a conveyor belt, but relied on ponies to haul coal tubs from the face to the slope where a hoist hauled the tubs to the surface.〔''The Last Pony Mine'', a documentary film, Les Benedict, director, Steve Knudston, producer, 1972. Available on YouTube in 3 parts (part 1 )(part 2 )(part 3 )〕 Longwall mining has been extensively used as the final stage in mining old room and pillar mines. In this context, longwall mining can be classified as a form of retreat mining. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Longwall mining」の詳細全文を読む スポンサード リンク
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