| 摘要 |
PROBLEM TO BE SOLVED: To effectively take reaction during inner excavation by rotating an auxiliary earth auger with a diameter enlarging drilling head by an auxiliary auger driver disposed at a leader mast, and fixing a diameter enlarging cutting edge into the ground to serve as an anchor. SOLUTION: At least one side part of a leader mast 63 is provided with a guide rail spaced by about 90 deg. from a main earth auger 66 with the leader mast 63 as the center, and an auxiliary auger driver 68 is elevatingly disposed at the guide rail. An auxiliary earth auger 69 is connected to the auxiliary auger driver 68. An underground hole 70 of specified depth is drilled by a diameter enlarging drilling head 1 at the lower end part of the auxiliary earth auger 69. A diameter enlarging cutting edge 7 is extended in the outer diameter direction of the underground hole 70 so as to be fixed as an anchor in the ground to take reaction when drilling with the main earth auger 66. Work execution can thereby be easily completed only by erecting the leader mast 63 on the ground and suspending and supporting it from a truck crane vehicle 60, and work can be executed even at a construciton site which a crawler crane vehicle cannot enter.
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