Coal mining in Illinois . ging from and supported by theshaft pillar. Consequently the roof will break at the shaft-pillar. The subsidence of roof following this break continuesviolently for three weeks and more gradually for a year. Fig. 21. Entries in shaft pillar in longwall mine Unless the entry-around-pillar is protected by a pack wall orcoal pillar, it will be closed by this first violent roof the entry-around-pillar has been established, openings9 feet wide as shown in fig. 21, which is a sketch of an actualshaft pillar, are driven into the coal face a1 intervals usuall
Coal mining in Illinois . ging from and supported by theshaft pillar. Consequently the roof will break at the shaft-pillar. The subsidence of roof following this break continuesviolently for three weeks and more gradually for a year. Fig. 21. Entries in shaft pillar in longwall mine Unless the entry-around-pillar is protected by a pack wall orcoal pillar, it will be closed by this first violent roof the entry-around-pillar has been established, openings9 feet wide as shown in fig. 21, which is a sketch of an actualshaft pillar, are driven into the coal face a1 intervals usually 96 COAL MINING INVESTIGATIONS of 42 feet. When these openings have progressed 15 feet,cuts 9 feet wide are made on each side of each opening at aright angle and are driven until the cut at the left of one open-ing meets the cut driven from the right of the one cuts serve the double purpose of establishing the long-wall face and of leaving a 15-foot coal pillar for the protectionof the Fig. 22. Pack walls around shaft pillar in longwall mine Sometimes when it is feared that the coal of the shaftpillar and entry pillar may spall off into the roadway a stripof coal 15 feet wide is sliced off completely around the shaftpillar as shown in fig. 22 and is replaced by a pack wall. The15-foot pillar left for entry protection is also replaced by a MINING PRACTICE 97 pack wall. The method of blocking out the shaft pillar bydriving narrow entries around it is in general use, but occa-sionally entries 27 feet wide are driven around the pillar,and two pack walls are built as the entry advances. One packwall 12 feet wide is built alongside the shaft pillar, and one6 feet wide on the future longwall face, leaving a haulageroad 9 feet wide between the two walls. The necessary open-ings through the walls are left for haulage. From the timewhen both hoisting shaft and air shaft reach the coal, 7 to 10months are required for driving entries through the shaftp
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
