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BORING PATTERN FOR EACH ROCK GRADE FOR MINIMALLY REDUCING OVERBREAK OF A TUNNEL GENERATED IN BLASTING THE TUNNEL BY BORING DIFFERENTLY A GAP BETWEEN PERIMETER HOLES AND A GAP BETWEEN THE PERIMETER HOLE AND A HEATING HOLE ACCORDING TO THE GRADE OF ROCKS
BORING PATTERN FOR EACH ROCK GRADE FOR MINIMALLY REDUCING OVERBREAK OF A TUNNEL GENERATED IN BLASTING THE TUNNEL BY BORING DIFFERENTLY A GAP BETWEEN PERIMETER HOLES AND A GAP BETWEEN THE PERIMETER HOLE AND A HEATING HOLE ACCORDING TO THE GRADE OF ROCKS
PURPOSE: A boring pattern for each rock grade for reducing overbreak of a tunnel is provided to prevent the concentration or reduction of explosive force of powder on the rock by boring a space gap of perimeter holes and a burden to a heating hole. CONSTITUTION: A boring pattern for each rock grade for reducing overbreak of a tunnel is composed of perimeter holes(10) bored at regular intervals along a contour line(E); a heating hole(20) spaced from the perimeter hole at a burden(B) in the perimeter hole, and plural central blast holes bored in the heating hole. The perimeter holes are bored with keeping a gap differently according to the grade of rocks to minimize overbreak.
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