Coal mining in Illinois . ng a flathook at one end and a hole at the other to receive the hookof the next sheet. The chute is moved forward daily as theface progresses. In several mines cross-entries are drivenoff at an angle of 70 degrees with the main entries for thepurpose of increasing the size of the cog built to supportthe roof over the switches at the junction of main roadwayand cross-entries. Table 10 gives dimensions of workings ateach mine examined. MINING PRACTICE 101 In all classes of longwall operation the same generalmethod of filling the space left by the removal of the coal pre
Coal mining in Illinois . ng a flathook at one end and a hole at the other to receive the hookof the next sheet. The chute is moved forward daily as theface progresses. In several mines cross-entries are drivenoff at an angle of 70 degrees with the main entries for thepurpose of increasing the size of the cog built to supportthe roof over the switches at the junction of main roadwayand cross-entries. Table 10 gives dimensions of workings ateach mine examined. MINING PRACTICE 101 In all classes of longwall operation the same generalmethod of filling the space left by the removal of the coal pre-vails. The rock obtained from brushing the roof, that whichremains after building pack walls, and the clay obtained fromundermining the coal are thrown behind the pack walls liningthe roads. The space between the pack walls and also thewaste material itself is called the gob. The gob area is usuallyfilled with rock and clay to within 2 to 5 feet of the coal loose rock and clay helps to support the roof and con-. FlG. 25. Face of longwall panel mine in clipping seam (photo by H. I. Smith,U. S. Bureau of Mines) trol the roof weight on the coal face. After the first break atthe shaft pillar and face—if the gob area has been properlyfilled so that the roof weight rides on the face of the coal—other roof breaks occur every 2 inches to 6 feet parallel to thecoal face and extending upward away from the face andtoward the gob as the face advances. The distance betweenbreaks depends principally upon the character of the roof andthe packing of the gob. With proper packing the distancebetween breaks should correspond to the width of coal brought 102 COAL MINING INVESTIGATIONS down. At the face of solid coal the cracks in the roof aredifficult to see, and they do not become easily visible until theface has advanced 4 to 5 feet. The distance to which these mining breaks extend intothe roof depends upon the roof material, but they rarely ex-tend more than 15 feet above the coa
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcoalmin, bookyear1915
