PURPOSE:To extend the drilling depth and facilitate the soil discharging work on the ground by the shrinkage of an auxiliary kelly bar by providing the telescopic auxiliary kelly bar between the main kelly bar and a drilling bucket of an earth drill. CONSTITUTION:After a bucket 41 is removed from a main kelly bar 25 and an auxiliary kelly bar 10 is fitted at the lower end of the main kelly bar 25, the bucket 41 is fitted. A main rope 41 and an auxiliary rope 27 are delivered to lower the auxiliary kelly bar 10, and the bucket 41 is located at the bottom section of a hole HL. When the main kelly bar 25 is rotated, an outer kelly bar 11 is rotated, the rotation is transmitted to the second kelly bar 12 and an inner kelly bar 13, and drilling is performed by the rotation of the bucket 41. A deeper hole is drilled by the extension of kelly bars 12 and 13, and soil is discharged by the shrinkage of the auxiliary kelly bar 10. The work efficiency can be sharply improved.
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