Full Download Panel System of Coal Mining: A Graphical Study of Percentage of Extraction (Classic Reprint) - C M Young file in ePub Online

Excerpt from Panel System of Coal Mining: A Graphical Study of Percentage of ExtractionWhile no general rule can be stated for the determination of the dimensions of pillars and of the ratio of pillar area to room area necessary for the permanent support of the surface at a given depth, it is known that the relative area of pillars must be made greater as the depth