Coal mining in Illinois . uch rock work must be done the costis higher. At a mine in District IV where considerable rockwork was necessary in placing sets an entry-set composedof a 10-inch 35-pound steel I-beam 16 feet long on 8-inchwhite-oak legs costs approximately $ in place. The costof setting timber and steel collars is about the same. Thestandard relation in Illinois between span and diameter ofround white-oak crossbars or size of steel I-beams is: Diameter of round Span in feet white-oak timbersin inches I-beams 10^2 pound; 4-inch 8 6 or18 pound; 8-inch 17^4 pound; 6-inch10 7 or 8
Coal mining in Illinois . uch rock work must be done the costis higher. At a mine in District IV where considerable rockwork was necessary in placing sets an entry-set composedof a 10-inch 35-pound steel I-beam 16 feet long on 8-inchwhite-oak legs costs approximately $ in place. The costof setting timber and steel collars is about the same. Thestandard relation in Illinois between span and diameter ofround white-oak crossbars or size of steel I-beams is: Diameter of round Span in feet white-oak timbersin inches I-beams 10^2 pound; 4-inch 8 6 or18 pound; 8-inch 17^4 pound; 6-inch10 7 or 8 or 18 pound; 8-inch TIMBERING 133 Span in feet 12 Diameter of roundwhite-oak timbersin inches Size and weight of SteelI-beams 18 pound; 8-incl 14 10 40 pound; 8-inch 16 18 12 14 40 S2_ 52 70 pound; 8-inch orpound; 12-inch pound; 12-inch orpound; 18-inch Witn this relation frames are usually spaced on ly^-footcenters. Eight-inch diameter rough white-oak legs are usedwith spans of 8 and 12 feet and 10-inch legs are used for. Fig. 39. Inby end of concrete-lined bottom greater spans. It is not certain that for entry timberingsteel legs are economical. The cost in place of a 4-inch 28-pound steel leg 6 feet long is approximately $ An 8-inchround white-oak leg 6 feet long costs about 80 cents at the pitmouth. Inasmuch as sets fail in the crossbars when not sub-jected to lateral presure and the labor cost of replacing a legis small the use of steel legs may entail an unnecessary ex-pense. Old railroad and streetcar rails are used as crossbars inDistricts IV, VI, VII and VIII. Old rails have been pur- 134 COAL MINING INVESTIGATIONS chased in one district for $12 per ton. When bought forroof support their weight varies from 50 to 75 pounds peryard. In District VIII 60-pound rails used as crossbars failedunder the roof weight. No rail lighter than 70 pounds peryard should be used under heavy roof presure and even heavyrails are inferior to I-beams because their carbon content ishigh
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
