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Comment by ant6n | Hacker News Reader

Plenty of subways get built in bedrock. Its a bit more expensive to tunnel, but not unusual at all. It’s not so easy to use tunnel boring machines, but you can blast. Its also possible to make station caverns right in the rock.

Btw, the tunnels aren’t the biggest cost of subway systems. Maybe 15-30%. I think the biggest tickets are usually the stations.

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As pointed out in part 2, the 2nd Avenue stations are grotesquely large. Sure they are pretty but I’d rather have 4x ugly stations.

Large stations are not just unnecessarily expensive, they usually take longer to walk through. Looks nice on opening day, and then a hundred thousand people waste an extra 2 minutes every single day forever.

I'd rather have quad tracks. easier to keep things running 24/7.

I'm not sure if underground blasting is a good idea when there are skyscrapers nearly a century old aboveground. Hard enough to assume recent building haven't had someone in the loop cutting corners (e.g. concrete that isn't as robust as expected), the old stuff had zero checks during constructions and definitely no computer aided simulations.

Honestly it's a miracle that skyscraper collapses are so rare.

Second ave has little in the way of skyscrapers. It’s mostly residential and small shops.

But consider that tunnels are created through mountains (far heavier). Done right, I doubt it’s an issue.

It's really not a problem. Controlled blasting around vulnerable or weak structures is well studied and practiced by professionals. Computer aided design and modeling has only gotten better over the years.

NYC in particular has some very stringent regulations regarding blasting, allowable vibration levels, and so on. Long gone are the days of gung-ho cowboys lighting off fuses leading to piles of dynamite, massive fireballs, and the like.

Example reading: https://core.ac.uk/download/pdf/229071708.pdf

https://www.researchgate.net/publication/328666110_Large_str...

https://www.researchgate.net/publication/297751622_Strains_I...

https://www.researchgate.net/publication/315527348_Reducing_...

E: Trying to find a paper about blasting a road tunnel in Turkey under some ancient ruins. The stringent restrictions they were under and the things they did to maintain compliance were really, really interesting (as a blasting engineer) but I can't find the damn thing right now.

They’re not built for the same capacity, however.

Ironically I think the city may shrink in the coming years, thanks to Covid and the upcoming fiscal crisis.

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