| 摘要 |
PROBLEM TO BE SOLVED: To prevent the generation of a widely recessed part on the side surface of a cover plate as well as to reduce the vertical difference of the cover plate so that work may be safely performed while an operator gets on a pit cover. SOLUTION: In this pit cover 4 composed of a cover plate having an extendable multiple layer structure, cover plates 4a to 4e are formed into inverted U-shaped sections, the radii of curvature of arches of shoulder parts of the cover plates 4a to 4e are so set that the inner cover may has the larger radius of curvature, and relief clearances 4bc to 4de are formed between mutually adjacent cover plates. Moreover, first engaging protrusions 6c to 6e and second engaging protrusions 7b to 7d to be engaged with one another are formed between the front ends or the rear ends of respective cover plates 4a to 4e and the relief clearances 4bc to 4de.
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