| 摘要 |
PURPOSE:To conduct safe positive execution by forming a protruding section with a stepped section at the central section of a cutter face and driving and propelling the cutter face. CONSTITUTION:A coaxial protruding section 4, which has a pre-stage cutter face 6 and the post-stage cutter face 8 of a doughnut section 7 and has a small diameter, is shaped to the front end face of a shield 2. The cutter faces 6, 8 are reversely rotated mutually and driven respectively. Soil and sand taken in are housed in a camber, and transported backward by a transport means. Accordingly, an effect on a peripheral ground is inhibited, thus safely allowing execution positively. |
