Coal mining in Illinois . 3y2 or 4 inches in diameter are usually bought. Fromy2-cent to 1 cent per linear foot is paid for props and thenumber used per ton of coal mined varies from 1% to 3. Table 15.—Cost of mine timbers in District I LengthFeet DiameterInches Average costCents 6 7 8 OOOOO 151680 10 14 10 12 125190 The expense of cross bars increases rapidly with in-creased diameter and length of span. Table 15 gives aver-age cost in the longwall district of mine timbers of variousdiameters and lengths. These figures do not include thecost of placing in position but refer only to th
Coal mining in Illinois . 3y2 or 4 inches in diameter are usually bought. Fromy2-cent to 1 cent per linear foot is paid for props and thenumber used per ton of coal mined varies from 1% to 3. Table 15.—Cost of mine timbers in District I LengthFeet DiameterInches Average costCents 6 7 8 OOOOO 151680 10 14 10 12 125190 The expense of cross bars increases rapidly with in-creased diameter and length of span. Table 15 gives aver-age cost in the longwall district of mine timbers of variousdiameters and lengths. These figures do not include thecost of placing in position but refer only to the timbers aspiled on the surface. TIMBERING 131 ROOM-AND-PILLAR TIMBERING Timbering* in unmodified room-and-pillar and panel minesin Illinois is characterized by excessive waste in spite of thesteadily decreasing timber supply and constantly increasing-cost of mine timber. Generally no attempt is made to saveroom props by pulling them after rooms have holed throughand props are abandoned even though they could easily be. FlG. 38. Shaft bottom with roof supported by steel I-beams set on concretewalls (photo by K. Y. Williams, I S. Bureau of Mines) pulled at small cost. The high cost of white-oak props ofstandard 41/2~inch diameter for lengths up to 5 feet has ledto the false economy of buying props of poor quality andsmaller diameter. This is especially true in District V wheremany operators buy shipments in which less than one per-cent of the props are white-oak, the remainder consisting ofred oak, water oak, elm, hickory, sassafras, and hemlock 132 COAL MINING INVESTIGATIONS with an average prop diameter of only 3% inches at thesmall tip. At very few mines is preservative treatment given per-manent timbers, and these mines are principally in DistrictIV. At one time in this district where loss by decay hasbeen heavy timbers are treated with one gallon of creosoteper cubic foot. Untreated round, white-oak timbers with asmall end diameter of 10 inches cost 10 cents per runningf
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
