| 摘要 |
PROBLEM TO BE SOLVED: To provide a casing tube excellent in penetration property into the ground. SOLUTION: The casing tube comprises upper, inner and outer cylinders 1, 2, lower, inner and outer cylinders 5, 6 whose base ends are connected to tips of the upper, inner and outer cylinders 1, 2 via connection rings 3, 4 in an oscillating manner along the axial direction, a bit 8 mounted on a connection plate 7 to close tips of the lower, inner and outer cylinders 5, 6, bearings 9, 10 whose inner rings 9a, 10a are fitted to an outer circumferential surface of the lower inner cylinder, a weight 11 which is arranged between the lower, inner and outer cylinders 5, 6 and fixed to an outer circumferential surface of outer rings 9b, 10b, a pinion 13 engaged with an inner gear 10c formed on the outer ring 10b of the bearing 10, and a drive motor 12 to rotate the pinion 13. By moving the weight 11 along the circumferential direction of the lower, inner cylinder 6, the precession is generated in the lower, inner and outer cylinders 5, 6 by the inertia of the weight 11 to realize the oscillating condition.
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