| 摘要 |
PROBLEM TO BE SOLVED: To form a drilled hole in concrete, which drilled hole has a modified cross-section of which inner diameter of the inside is long. SOLUTION: A high pressure pump unit 14 is used when the drilled hole 12 for burying an anchor is formed in the concrete body 10. The high pressure pump unit 14 is connected with a water tank 16, and is connected with a cavitation nozzle 20 through a high pressure hose 18. The nozzle 20 is for jetting cavitation jets in the air, and has a high pressure nozzle portion and a low pressure nozzle portion. When the high pressure water and low pressure water are jetted from the nozzle 20, the cavitation jets are generated in the air, and bubbles are generated from the cavitation jets. The bubbles collides with the concrete body 10 and is broken to generate high impact pressure, so that the drilled hole 12 is formed in the concrete body 10 by the impact pressure. The drilled hole 12 has the modified cross section of which inner diameter of the inside is longer than that of the surface.
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