| 摘要 |
PROBLEM TO BE SOLVED: To provide a formation method of a trench to a bedrock capable of surely forming the trench continued to the bedrock by using a special bit in order to make the second hole connected to the other first hole adjacent to the first hole to be widened. SOLUTION: In the formation method of the trench (12) made in the bedrock before the trench (10) is excavated, a plurality of first holes (16 and 18) are bored in the bedrock at an interval and in parallel with each other, one (16) of the first holes is widened to make it as the second hole (20) coming into contact with the other (18) of the first holes adjacent to one of the first holes so that the bit (22) can be rotationally driven, and the bit (22) equipped with a main body (24) partially accepted in one of the first holes and having the surface formed in a tapered conical-shape or a semi-spherical shape so that core controlling action is received from the circumferential wall thereof and a plurality of chips (26) mounted on the surface of the main body is used to excavate the circumferential wall of one of the first holes. COPYRIGHT: (C)2006,JPO&NCIPI
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