pillar(redirected from Pilla)
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part of a bed or seam of a mineral that is left untouched when working a deposit in order to support the roof and protect mine excavations and surface structures.
Based on their purposes various types of pillars are distin guished: protective pillars (between levels, above and below drifts, between chambers), which protect objects during mining operations; fire safety pillars, which separate individual parts of the mine field from one another and help contain the fire, should it begin, within small areas; barrier pillars, which prevent surface or subterranean waters, gases, or loose silt from an excavation or unused mine from entering working mines; and support pillars, which prevent the rocks of the roof of the seam or ore body from caving in into an excavated area. The pillar size depends on the mining-geological conditions and the purpose of the pillar and is built according to standard guidelines.