| 摘要 |
PURPOSE:To prevent a direction correcting function from being influenced by a soil condition by pivotally fitting a top edge head to a yoke formed at the front edge of a direction correcting cylinder, and forming a slope between the top edge head and yoke. CONSTITUTION:A direction correcting cylinder 6 is contracted in a leading pipe 1 to make the rear edge of a top edge head 2 come into contact with a front edge of the leading pipe 1. In this condition, the leading pipe 1 is driven into the ground with a small-bore pipe. When the leading pipe 1 is shifted from a planning line and a direction need to be corrected, the direction correcting cylinder 6 is made to go forward, and then the small-bore pipe is made start to drive forward again. At this time, the top edge head 2 which has received earth pressure rotates around a pin 4, and its neck is oscillated in a driving direction until the yoke 5 has come into contact with a slope 2f formed at the projecting part 2d of a bracket 2c. A driving direction of the leading pipe 1 is corrected in the direction in which the top edge head 2 has been oscillated. Then the direction correcting cylinder 6 is contracted in the leading pipe 1, and the small-bore pipe is driven forward again. It is thus possible to correct any direction by the single direction correcting cylinder 6. |
