I'm making 2 suggestions because you haven't given enough context.

"blind arches" is an architectural term describing an arch that isn't an open but is intentionally filled with stone or brickwork. "bricked-up arches" might fit with your context, if the de-mining and clearing-out operations require personnel to search for bricked-up arches.

That's the best I can do, in the absence of more context- you decide which option works better.

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Note added at 14 mins (2009-07-09 18:59:07 GMT)
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"bricked-up arches" = arches that were originally open but were bricked up or closed, at a later stage.