alt Hacker NewsThe rock they dug through for Koralm is, no hyperbole, about as bad as it gets. It's the gnarliest part of what's under the Alps and required them switching back and forth between boring and blasting.
Being two separate tunnels, it also needs twice as much excavation work. It's also ~25x deeper than Toei Oedo (4000ft vs 157ft). At 4000ft the rock itself is 45-50C!
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It's also really hard to make the tunnel remain a tunnel over its expected 150 year lifespan - given that it basically runs through a fault line. They had to study and test local geology for about 15 years, build certain sections to expect some movement over time, as well as kit everything out with a lot of sensors.
Overall an amazing achievement, and unsurprising it took this long to figure out!
Good point about "boring vs blasting". I didn't think about that. I remember reading about the longest tunnel in Japan between Honshu and Hokkaido (Seikan Tunnel). I recall that it was entirely hand drilled due to unusual soil conditions. I wonder if that would still be true today with state of the art tunnel boring machines.
> Being two separate tunnels, it also needs twice as much excavation work.
The Koralm tunnel has a different temperature gradient, as the depth is a consequence of a mountain on top of the tunnel, rather than an increased proximity to the earth crust/core.
32°C is still a significant engineering concern, but not as consequential as 45–50°C.https://www.sciencedirect.com/science/article/pii/S088677982...