| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent the generation of a difference in excavation resistance between drilling rods and the occurrence of a blank shot when a slot in which a plurality of holes are arranged in series is formed on a base rock with a plurality of drilling rods arranged in parallel. <P>SOLUTION: Each bit head 44 of a plurality of drilling rods is formed into an ellipse shape viewed from the axial direction, and the rotational loci of tips on the ellipse long axis side of the adjoining bit heads 44 are caused to cross to each other. The plurality of drilling rods are rotated synchronously so that the adjoining bit heads 44 do not interfere with each other. <P>COPYRIGHT: (C)2013,JPO&INPIT |
