Sure, bedrock would slow a project down but it wouldn't explain the higher level of labour. If you are moving more slowly, you need less people to keep the supp

Sure, bedrock would slow a project down but it wouldn't explain the higher level of labour. If you are moving more slowly, you need less people to keep the supply chain moving, not more. I saw a TV show with a standard Tunnel Boring Machine and it was about 5 men operating it (plus the automated materials feed). Even if they were paid $1M a year, it would still be loads cheaper than these tunnels are costing New York.