To smoothly excavate pile shafts of an appropriate depth with a low amount of soil excavation to the surface.
A drum-shaped steel pipe 1 is provided with upper and lower end plates 2 and 3. The lower surface of the lower end plate 3 is provided with such a spiral blade 4 as to reach the outer circumferential surface of the lower plate 3 in the direction of left rotation from its center part toward the tangential direction of the lower end plate 3. The lower surface of the spiral blade 4 is provided with a circular flange 6. One end of a notch part 7 formed in the flange 6 is bent downward in the direction advancing downward at right rotation in the bound excavator. An inclined groove 9 is formed in the outer circumferential surface of the drum-shaped steel pipe 1 in the direction advancing downward by right rotation. The groove 9 has openings 10 and 11 in the lower end plate 3 and the upper end plate 2. A rotation adjusting plate 13 which closes a part of the opening part 10 against the force of a spring 12 upward from below and is opened downward from above by the force of the spring 12 is pivoted at a lower part of a preceding edge at right rotation in the opening part 10 of the lower end plate 3, and a relieve gap (t) is interposed in the opening part 10 when the opening part is in a closed state in this low-soil-excavation ground excavator.
Nobutaka Fujii
Shigeo Fujii
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