| 摘要 |
A method for excavating a tunnel rock face by drilling a pattern of lift er holes and line holes. The line holes ensure the grade or slope of the excavation meets specification while reducing the need for cleaning out the face. A longitudinal band of lifter holes is drilled into the tunnel face at an acute angle in relation t o the substantially perpendicular reference axis emerging from the tunnel face. A series of line holes, disposed opposedly adjacent to the lifter holes, are drilled at a smaller acute angle. The lifter holes are drilled deeper than the line holes and they do not intersec t. Explosives are loaded into the lifter holes. The line holes are expendable and encourage fracturing of the rock.
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