| 摘要 |
<p>In an apparatus for forming horizontal subterranian holes there is described a broaching head, comprising a central shaft, a plurality of radial ground-cutting vanes extending from the shaft, first and second circumferential ground-cutting blades spaced from and extending around the shaft and co-axial therewith, the first of said blades being disposed forwardly of the second blade, and the first circumferential groundcutting blade being spaced at a greater distance from the shaft than the second blade.</p> |
