| 摘要 |
A lead pipe configuration for use in an underground piping device wherein a succession of lead pipes are propelled in a forward direction to guide pipeline lay down are provided with ring-shaped light shields in at least some of the lead pipes so that such light shield can block at least some of the light projected rearwardly from a direction correction head at a foremost tip of the lead pipe configuration that would interfere with axially directed incident light that is to be detected by a transit at the rear of the configuration, this detection being used to determine if lead pipe configuration direction error is present and if so that it be corrected. The lead pipes also can have a high light absorption coating such as a resin on the inner lead pipe surfaces to absorb reflected light that otherwise could interfere with proper light detection.
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