Bord and pillar mining is not particularly suitable for mining coal at very great depths, because of the size of pillars that have to be left. The main alternative is longwall mining, which has been practised for many years in the deep European mines, particularly in the United Kingdom and West Germany. Two parallel roadways (called 'gates') are driven through the coal seam normally between 200 and 300 metres apart. This distance effectively determines the length of the working face. The two roadways are joined by a drivage in the seam at right angles to them and this forms the working face (or longwall). The roof at the working face is normally supported by hydraulically powered roof supports.
from http://www.competition-commission.org.uk/rep_pub/reports/1982/fulltext/160c02.pdf
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