| 摘要 |
PROBLEM TO BE SOLVED: To drill an independent hole with a guide rod installed by modifying the guide rod to be inserted in a precedent hole drilled in bedrock. SOLUTION: In the guide rod 7 parallelly provided with a drilling rod 4 to the extremity of which a bit 3 drilling the bedrock is attached, the rod length is extended/contracted by mutually sliding a small diameter rod 7b and a large diameter rod 7a. In this way, as the guide rod 7 is contracted while bringing into contact with the bedrock, even an independent hole h3 can be drilled with the guide rod 7 being attached. Accordingly, on drilling a continuous hole and an independent hole, efficiency of the work can be improved. COPYRIGHT: (C)2004,JPO&NCIPI
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