| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the waste of resources by the fact that a circular casing is left back-filled, and to reduce construction costs.SOLUTION: A steel circular casing 10 which is pressed into a ground for excavating sediment inside it and constructing a shaft is formed of a lower casing 1 having drilling bits 4 at its bottom end and an upper casing 2 connectable to the lower casing 1 by bolts 5 and cotters 6. A junction part between the lower casing 1 and the upper casing 2 is formed as a connection structure consisting of a circumferentially shaped spigot 1a and a receptacle 2a, and a circumferentially shaped cut-off packing 3 is provided between the spigot 1a and the receptacle 2a of the connection structure. Thereby, although the lower casing 1 is back-filled after the shaft is constructed, the upper casing 2 can be recovered, thus eliminating the waste of resources and reducing construction costs. |
