| 摘要 |
PROBLEM TO BE SOLVED: To make drilling easier with accurate dimensions in radial direction by making jetting angles from a pair of nozzles variable respectively and adjusting in such a manner that the jetting angle with the vertical axis of a nozzle at the side where the attenuation factor of jet flow is larger than the jetting angle with the vertical axis of a nozzle at the side where the attenuation factor of jet flow is small. SOLUTION: A pair of nozzles 10 and 11 are provided in an insertion pipe 6, and a jetting angleαrelative to insertion pipe 6 of the nozzle 10 and a jetting angleβfor nozzle 11 are made variable. And jet flows J1 and J2 from the nozzle 10 and 11 are collided at the impact point T, and the jet anglesαis made larger than the jet angleβ. By selecting the jet anglesαandβappropriately, the forces of jet flows J1 and J2 are made equal at the impact point T, and excavating force outwardly is diminished. Thus, even though there are differences in passages of jet flows and laminated ground exists, the impact point of the intersecting jet flows can be always controlled properly thereby drilling accurate and smooth excavated hole.
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