| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to securely correct a bent hole in the midway of a drilling process and to drill a long hole. SOLUTION: In a prelining in which a pipe body is installed along a tunnel line ahead of the tunnel excavation, an outer pipe and an inner pipe are provided above the tunnel cross section and when drilled while imparting a thrust force accompanying a striking force to the extremity of the inner pipe, an inner pipe bit 10 having a shape to bring a bias force in the first direction (1) in the drilling direction in the relation with the drilling reaction of the ground is provided. Further, when drilling while imparting a thrust force accompanying a striking force, an outer pipe bit 20 having a shape to bring a bias force in the second direction (2) in the drilling direction in the relation with the drilling reaction of the ground is provided in the extremity of the outer outer pipe. When drilling a straight hole, the circumferential position is set so that the first direction (1) and the second direction (2) are formed in the opposite positions, substantially 180 degrees, when correcting a bent hole accompanying drilling process, the drilling is executed in the relatively circumferential changed state of the inner pipe bit 20 and the outer pipe bit 10. After the final drilling completion, the outer pipe is left in the ground. COPYRIGHT: (C)2004,JPO&NCIPI
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