. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ^ miles long, and ■ iukIc wilh the center line of tlic tunnel,and when the rock has been broken outby the electrically fired blast and re-moved, a linal set of holes, parallel tothe tunnel center line, are ilrilled and. VIEW TAKKN FROM INTERIOR OK is large enough for two tracks. Therock penetrated in driving this tunnelwas principally micaceous schist. A heading is practically a small tunnelusually driven in hard material at thetop of what will later on be the finishedtunne
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ^ miles long, and ■ iukIc wilh the center line of tlic tunnel,and when the rock has been broken outby the electrically fired blast and re-moved, a linal set of holes, parallel tothe tunnel center line, are ilrilled and. VIEW TAKKN FROM INTERIOR OK is large enough for two tracks. Therock penetrated in driving this tunnelwas principally micaceous schist. A heading is practically a small tunnelusually driven in hard material at thetop of what will later on be the finishedtunnel. A fairly accurate metal pictureof what a top heading is like, may behad by supposing the back sheet of awagon-top locomotive boiler to repre-sent the cross section of the finishedtunnel. In such an arrangement thatportion lying above the crown sheetwould correspond to the heading andthe rock would be taken out by the cen-ter cut system of blasting. This system consists of drilling, say,six holes in two vertical rows, of threeeach, about 9 or 10 ft. apart and at suchan angle that each pair shall meet orcross at the bottom. When these holesare fired, a vertical wedge-shaped quan-tity of rock is taken out. The squaringup process is carried on by drilling twovertical lines of holes a few feet fromthe edges of the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectrailroa, bookyear1901
