Coal mining in Illinois . t partings. Fig. 38 shows a shaftbottom at a mine in District VI where the roof is supportedby steel I-beams resting on concrete walls and fig. 39 showsthe inby end of a shaft bottom in District VIII which is linedthroughout with concrete. The walls of the lining are 24inches thick at the bottom and the thickness of concrete is TIMBERING 135 gradually reduced till at the crest of the arch it is 12 gob filling is packed between the arch and the roof. Thelength of concrete bottom on each side of the shaft is 165feet. The concrete was made in the following propo
Coal mining in Illinois . t partings. Fig. 38 shows a shaftbottom at a mine in District VI where the roof is supportedby steel I-beams resting on concrete walls and fig. 39 showsthe inby end of a shaft bottom in District VIII which is linedthroughout with concrete. The walls of the lining are 24inches thick at the bottom and the thickness of concrete is TIMBERING 135 gradually reduced till at the crest of the arch it is 12 gob filling is packed between the arch and the roof. Thelength of concrete bottom on each side of the shaft is 165feet. The concrete was made in the following proportions:1 Portland cement; 1 sand; 4 washed gravel. Proportionsfor concrete which are frequently used for massive work are:1 Portland cement; 1 washed sand; 4 sifted cinders. Fig. 40shows the point of the pillar at a cross entry in a mine inDistrict VI. The coal pillar is cut back 20 feet and the roofat the point is supported by a solid concrete pier. The chiefobject in removing the coal at pillar points and building brick. Fig. 41. Cog timbering at parting or concrete piers is to provide a substantial root supportwhich will not be knocked away if hit by a trip which happensto leave the track when rounding the curve. In a few large mines other than Longwall timber is usedinstead of concrete where a large bearing surface is one mine where wide partings are built the roof is sup-ported by cogs 8 feet square built of (i-inch props, as shownin fig. 41. These cogs are not filled with gob and are weakerthan filled cogs used in longwall mining in Illinois. In entries in nearly all mines the support under bad roofis the 3-piece entry set, either with two long legs, with < ne 136 COAL MINING INVESTIGATIONS leg short and the other long or with two short legs restingin latches cut in the ribs. Where a curve occurs in the entrythe short-legged frames are commonly used because a tripwhich jumps the track is likely to break the legs of long-legged frames and bring down bad falls
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
