| 摘要 |
PROBLEM TO BE SOLVED: To construct a plurality of ribs with accuracy. SOLUTION: Diameter enlarging devices 2 with expansion blade scrapers 20 openable/closable by hydraulic cylinders 3 are mounted to a rotary excavating shaft 10 in two or several vertical parts. A solenoid valve is mounted to a hydraulic hose to control the hydraulic cylinders 3, and the diameter enlarging devices 2 are simultaneously or separately operated to carry out diameter enlarging excavation to construct ring-like grooves in the peripheral wall of a pile hole. A plurality of ribs of high accuracy can thereby be constructed simultaneously or individually, and the pitch of the ribs is accurate.
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