Coal mining in Illinois . the company. When somepart of the face has been allowed to lag behind and the work-ing face has squeezed, the area is not usually cleaned up, butthe face is diverted to pass around the squeezed area, some-times leaving a small block of coal in the gob. The effect of the subsidence of the roof upon the over-lying strata and upon the surface after the coal has been 104 COAL MINING INVESTIGATIONS removed has not been clearly determined. Surface subsi-dence has been the subject of extended litigation. While itis undoubtedly true that there is subsidence of the strata im-m
Coal mining in Illinois . the company. When somepart of the face has been allowed to lag behind and the work-ing face has squeezed, the area is not usually cleaned up, butthe face is diverted to pass around the squeezed area, some-times leaving a small block of coal in the gob. The effect of the subsidence of the roof upon the over-lying strata and upon the surface after the coal has been 104 COAL MINING INVESTIGATIONS removed has not been clearly determined. Surface subsi-dence has been the subject of extended litigation. While itis undoubtedly true that there is subsidence of the strata im-mediately overlying the coal, opinion is divided as to the ex-tent of this subsidence. There are not sufficient data avail-able from which to formulate a general rule for the amountthat results from mining seams of different thicknesses lyingat different depts and under different kinds of cover. Work at the Face Room centers at the longwall face are usually 42 feetapart. Half-way between the center of the road head of each. Fig. 27. Props and sprags at face of longwall mine (photo by H. I. Smith,U. S. Bureau of Mines) room and the center of the road head of the adjacent roomsa prop called the march prop is set. The 42 feet of coalface included between two inarch props is called a recent years two miners worked at every place in alllongwall mines, but at present on account of the scarcity of MINING PRACTICE 105 labor probably one-half of the places in longwall mines con-tain only one miner. Upon the one miner or two miners, asthe case may be, assigned to a place, is the charge of properbuilding of pack walls along the roadway of the room, andof proper gobbing of the space between the marches. When the bed is underlain by fireclay, beginning at thecenter of the roadway each miner picks out the clay underthe coal and makes an undercut 8 to 12 inches high. Thisundercut sometimes extends 2 to 2y2 feet under the coal. Toprevent it from falling on the miner while he is unde
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915