| 摘要 |
PURPOSE:To make it possible to replace excavation bits on the way of excavation work. CONSTITUTION:An inner pipe 3, which is rotatively driven, is mounted inside a steering pipe 2 which is advancing underground. An inner pipe 11 is fixed with the tip of the inner pipe 3 inside the steering pipe 2. The inner pipe 11 is structurally integrated with an outer pipe 12 by way of a spline structure which comprises a groove and an projection. Both pipes are axially movable within a specified range and united in one piece in the rotary direction. Excavation bits 4 are installed to the tip of the outer pipe 12 in a rocking manner. When driving, if the inner pipe 3 is moved forward, the outer pipe 12 will run into an engagement part 7 of the jack pipe 2 so that it may be fixed. The inner pipe 11 slides forward against the outer pipe 12, thereby pressing the excavation bits 4 and setting the bits at the excavation position in front of the jack pipe 2. The ground is excavated by driving the jack pipe 2, rotating the inner pipe 3 and the excavation bits in front of the jack pipe 2. Even on the way of jacking, if the inner pipe 3 is pulled backward, the excavation bits 4 will be closed so that it may be possible to replace the excavation bits by pulling out from the rear end of the jack pipe 2. |
