| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to obtain a sand pile having a diameter larger than an inside diameter of a casing. SOLUTION: A casing 26 is provided on the surface of a land to form a sand pile. Then, the casing is forward rotated, the casing is penetrated through a specific depth in the ground and, at the same time, a feeder 32 is led into the ground together with the casing 26 and is positioned at a specific level. After the casing 26 is penetrated through the specified depth, a sand pile material is dumped in the casing 26 from a chute 24. Then, the feeder 32 is substantially kept in the specific level to reverse rotate the casing 26 while forward rotating the feeder, and the casing 26 is pulled up by a specific return-distance. After the casing 26 is pulled up, the casing 26 is kept in a position where the casing 26 is substantially pulled up, and the feeder 32 is pulled up by a distance equivalent to the return-distance while forward rotating the feeder 32.
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