| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a double pipe drilling device which eliminates the need for leaving an outer pipe underground and separately providing a boring machine that is not for drilling, and to provide a method of retracting the casing up to the ground. <P>SOLUTION: A ring bit (20) has a rotation transmission protrusion (N1) formed and a casing shoe (22) has a cutout part (N2) formed that allows the rotation transmission protrusion (N1) to enter. The rotation transmission protrusion (N1) has a function of entering the cutout part (N2) in retraction and coming into contact with the cutout part (N2) to transmit rotation of the ring bit (20) to the casing shoe (22) and an outer pipe (casing 24). <P>COPYRIGHT: (C)2012,JPO&INPIT |
