. Bulletin . sometimes advantageous todrive a small tunnel into the bank and to load this cavity with ex-plosives. Following is a description of a large blast of this char-acter made at a railroad cut in 1911. (See PL XIII, frontispiece.) The purpose of the blast was to remove a large mass of hard rockconsisting of a pegmatitic and biotitic granite that stood in the formof a point or nose about 55 feet high and 100 feet across. On ac- 56 A PRIMER ON EXPLOSIVES. count of the contour of the hill it was impracticable to erect 6-inchwell drills on top and follow the usual procedure in quarry blast
. Bulletin . sometimes advantageous todrive a small tunnel into the bank and to load this cavity with ex-plosives. Following is a description of a large blast of this char-acter made at a railroad cut in 1911. (See PL XIII, frontispiece.) The purpose of the blast was to remove a large mass of hard rockconsisting of a pegmatitic and biotitic granite that stood in the formof a point or nose about 55 feet high and 100 feet across. On ac- 56 A PRIMER ON EXPLOSIVES. count of the contour of the hill it was impracticable to erect 6-inchwell drills on top and follow the usual procedure in quarry blasting,as was desired, and therefore the tunnel method was adopted andcarried out as follows: PRELIMINARY EXCAVATION INTO THE ROCK MASS. A small tunnel, or drift, varying in width from 4 to 5 feet and inheight from 6 to 7 feet, was driven into the side of the hill to a dis-tance of 80 feet, and at the upper end of this drift one crosscut wasrun 65 feet to the right and ore crosscut 26 feet to the left (fig. 3)..
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectminesandmineralresou
