Coal mining in Illinois . , The roadway props are sawed off atthe top an inch at a time as the roof settles and new cap piecesare driven in. In some cases this sawing must be attended todaily and the roadways brushed every few days to keep themopen. As the roof settles the packs and shanties are com-pressed and squeezed into the fireclay till roof and floormeet. The shaft bottom is then widened and timbered. The advantages claimed for removing the coal aroundthe shaft are that the expense of timbering the bottom isreduced, and that the roof-weight begins sooner to ride on the 98 COAL MINING IN
Coal mining in Illinois . , The roadway props are sawed off atthe top an inch at a time as the roof settles and new cap piecesare driven in. In some cases this sawing must be attended todaily and the roadways brushed every few days to keep themopen. As the roof settles the packs and shanties are com-pressed and squeezed into the fireclay till roof and floormeet. The shaft bottom is then widened and timbered. The advantages claimed for removing the coal aroundthe shaft are that the expense of timbering the bottom isreduced, and that the roof-weight begins sooner to ride on the 98 COAL MINING INVESTIGATIONS working face. Those operators who leave coal for shaft pil-lars admit these advantages but reason that the uncertaintyof being able so to control subsidence that the shafts will notbe thrown out of plumb when the pillar is removed is toogreat. After the shaft pillar has been blocked out and re-moved and the longwall face established the work progressesregularly in a long continuous line. From each side of the. Fig. 23. Plan of longwall mine with auxiliary permanent entries centers of the openings which were left in the entry pillar thecoal of the face is removed. In order to provide for haulagefrom all parts of the face to the shaft, roadways 9 feet wide,called rooms, are maintained as shown in fig. 20, by building-pack walls of rock. These rooms are continuations of theopenings through the entry pillar, and the pack walls pro-tecting them are usually 12 feet thick. When pack walls arefirst made they are often spaced 10 to 12 feet apart to allow MINING PRACTICE 99 for bulging when the roof weight sets on them which causesnarrowing of the roadways. A track is laid to the face of eachroom. In order to save the expense of a road for haulagefrom the face of each room to the main entry in the shaftpillar, cross-entries maintained through the gob by pack walls,are turned off near the shaft pillar as shown in fig. 20 and in-tersect the rooms at an angle of 45 degrees. The
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
