looking at the drawings and specs some more, excavation as much as 19 metres below the existing ground. As much as about 14 metres into bedrock. The whole tunnel structure appears to be inside what is right now bedrock.
Simple, but massive, structure. A quick rough calculation show about 60,000 cubic metres of concrete. That's about 4 times as much as the raft slab for the Bow tower, or enough to make a block 100m x 100m x 6 metres high.
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