PURPOSE: To excavate an underground space having a smooth wall surface with high executability when the space of a tunnel, etc., is excavated at a baserock by blasting. ;CONSTITUTION: When a bore hole 2 of a long hole shape and a blasting hole 3 of a circular shape are perforated at each specific interval along an outer peripheral side 1 of a scheduled tunnel T, the hole 2 is perforated at a part in which a discontinuous surface 5 such as a joint, a fault, etc., existing at the baserock is crossed at the side 1, and the hole 3 is perforated at a position shorter than a distance from an end of the bore hole to the surface 5 along the side. Gunpowder is charged in the hole 3 and blasted to form a tunnel wall surface along the side 1 and to excavate the baserock surrounded by the wall surface by blasting.;COPYRIGHT: (C)1995,JPO
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