| 摘要 |
PROBLEM TO BE SOLVED: To erect a casing pipe, particularly in a soft layer such as a mudstone layer or soft rock layer, without using a diameter-increasing bit. SOLUTION: A stepped part 16 that is one step smaller in diameter than the rear end of the inner peripheral part of a casing pipe 13 is formed at the front end of the inner peripheral part of the casing pipe 13, and an abutment part 12 capable of abutting against the stepped part 16 along an excavating direction is provided on the outer periphery of an excavating tool 1. By making the outside diameter of the abutment part 12 smaller than the inside diameter of the rear end of the inner peripheral part of the casing pipe 13, the excavating tool 1 is oriented in its excavating direction and engaged with the casing pipe 13 so that the excavating tool 1 can advance integrally and move backward in the excavating direction relative to the casing pipe 13. The end 2 of the excavating tool 1 and the edge of the casing pipe 13 constitute excavating parts 9, 17, and as a borehole is formed by the excavating parts 9, 17, the casing pipe 13 is erected in the borehole.
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