. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . o drill holes so that a blast willdo effective work. When a solidface of rock must be broken into^^ as in a tunnel-heading, the workis necessarily ineffectual and ex-pensive. A conical or wedge-shaped mass will first be blownout by simultaneous blasts inthe holes marked 1, Fig. 67;blasts in the holes marked 2 and3 will then complete the cross-section of the heading. A great saving in cost may often besecured by skilf
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . o drill holes so that a blast willdo effective work. When a solidface of rock must be broken into^^ as in a tunnel-heading, the workis necessarily ineffectual and ex-pensive. A conical or wedge-shaped mass will first be blownout by simultaneous blasts inthe holes marked 1, Fig. 67;blasts in the holes marked 2 and3 will then complete the cross-section of the heading. A great saving in cost may often besecured by skilfully taking advantage of seams, breaks, and irreg-ularities. When the work is economically done there is but littlenoise or throwing of rock, a covering of old timbers and branchesof trees generally sufficing to confine the smaller pieces whichwould otherwise fly up. 152. Amount of explosive. The amount of explosive requiredvaries as the cube of the line of least resistance. The bestresults are obtained when the line of least resistance is | of thedepth of the hole; also when the powder fills about ^ of the average rock the amount of powder required is as follows:. DRILL HOLES IN TUNNEL HEADINGFig. 67. Line of least resistance 2 lb. 4 lbs. 6 lbs. 8 ft. Weight of powder 16 lbs. Strict compliance with all of the above conditions would re-quire that the diameter of the hole should vary for every this is impracticable, there should evidently be somevariation in the size of the hole, depending on the work to bedone. For example, a 1 hole, drilled 2 8 deep, with itsline of least resistance 2. and loaded with ^ lb. of powder, would i^^ KAILROAD CONSTRUCTION. § 153. be filled to a depth of 9^, which is nearly | of the depth. A3 hole, drilled 8 deep, with its line of least resistance 6y andloaded with 6| lbs. of powder, would be filled to a depth of over28, which is also nearly ^ of the depth. One pound of blasting-powder will occupy about 28 cubic i
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Keywords: ., bookauthorwebbwalt, bookcentury1900, bookdecade1920, bookyear1922
