Dylan Edwards (asker) Oct 3, 2009:

Thank you for your comments. I'm afraid there's very little context.

I've just had a look at this: http://www.meadwaypark.co.uk/TunnelComplete/index.html
and I see that "segments" or "half-segments" are mentioned.

egm Sep 27, 2009:

Well, the way you present it, it's a 50/50 call. However it is mentioned at your text above the right column wall. And that makes me think that half segmentation wall is eventually the wall that covers the columns at the right side of the entire project. Still as you say, it could also be the middle frame, that separates the two tunnels, and to that they may be reffering. It is basically matter of how you read the blueprints. Trust me on this, I know a few things about engineering. If you can give me a few more clues, I might be able to identify the whole thing.

Dylan Edwards (asker) Sep 27, 2009:

cut-and-cover Cut and cover: a trench is excavated and then roofed over. So it isn't a tunnel in the strict sense of a bored tunnel. In this cut-and-cover structure, there are railway tracks going in both directions. Two tracks on each side, I think. There may be a dividing wall in the middle. Could πλάκα ημιδιατομής possibly mean the dividing wall in the middle, or is it definitely at the side?