| 摘要 |
<p>The assembly has a shell installed in a trench (10) and comprising rollers (82), and a movable frame to be placed above the shell. The shell has mechanical, electronic and electrical units housed in a drum (18) that is closed by a cover (28) comprising a circular opening (40) to reserve passage of retractable boundary marker (42). The marker has a ring (64) comprising two inner threads (66, 68) for assuring connection to the frame.</p> |
