Excerpt from Panel System of Coal Mining: A Graphical Study of Percentage of Extraction While 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 increases. Experience in Illinois shows that the surface cannot be permanently sustained over the deeper and thicker beds of the State unless about half of the ...
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Excerpt from Panel System of Coal Mining: A Graphical Study of Percentage of Extraction While 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 increases. Experience in Illinois shows that the surface cannot be permanently sustained over the deeper and thicker beds of the State unless about half of the coal is left. This statement is true in general for Districts V, VI, and VII, of the Illinois Coal Mining Investigations, which include bed 5 in Saline and Gallatin counties and nearly all mines in the No. 6 coal. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at ... This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
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