The tunnel boring in Seattle began right at the edge of downtown, went under a highway and a monumental retaining wall (They covered that wall with surveying targets and monitored it the entire time), then pretty deep under a residential neighbhorhood and a canal.
I think the only time it's moving close to high-rises again is over by the University.
Edit: I believe they went so deep because of the volume of glacial deposits in this area. Otherwise they would have been going through gravel. That made building the stations a bit of a pain (the Beacon Hill station still has chronic problems with water. It smelled like a moldy towel for a long time).
Here in Seattle the underground part of the city is open for tours (parts of it anyways). They built the current downtown on top of the old one, so it's pretty surreal down there.
Not even tunnels in this case, just like a whole-ass other set of streets and storefronts, all abandoned, partially buried, and covered on top.
Amazing that they managed to fill two whole pages of speculation about what might be under that bit of Seattle without once mentioning the giant underground city that actually is under that bit of Seattle. Or at most a few blocks away:
They talked to the local city librarian, so clearly she must have mentioned the tourist attraction where you can go down and see all the buildings that sank into the mud before they decided to raise the street level, oh, around 45 feet.
So now when they're digging a new tunnel 45 feet under that spot, it's tough to understand why they're in any way surprised that they hit something building-ish.
Seattle left the buildings where they were and raised the ground to what had been the 2nd floor level, creating buried tunnels underground to the old entrances[0].
I laughed when I saw the map. Compare [1] from the article with [2], which mostly corresponds to the location of the Seattle Underground.
I went on the Underground tour earlier this year. It's really interesting and pretty funny too; after a large earthquake at one point they used the tunnels to hide a lot of the debris. I'd definitely recommend the tour; that said, I would definitely not want to be down there when something like this hits the wall!
It's also 12 stories deep in the ground.[1] I was also looking for the other dimensions for the tunnel. It's just crazy to think about digging holes like that. Just like the Channel Tunnel along the English Channel. Insanity is just the name of the game when it comes to Tunneling.
The length of the tunnel doesn't have much to do with earthquake survivability, beyond the obvious linear scale factor. What the tunnel is tunneling through has a lot to do with it.
Seattle's geology is somewhat different from any of the usual cited examples, as we've learned by watching everyone from journalists to politicians to engineers stand around with dumbfounded looks while the Bertha saga unfolds.
Cool to see a weird piece of history from the hometown on HN. Many of those tunnels were used to run utilities and fiber so they still have usefulness, but it is sad to think about "what could have been" if many American cities had gone further with these kinds of projects.
Denver has these, you can see them on Larimer and Market street in LoDo. Around the 1890s, the locals dug out a series of tunnels through the city. The snows would come in and people would just go underground for a few days for business. There was a bar that closed about a year ago called the Blake Street Vault—it used to be a bank—and if you asked they would take you into the basement to see the vault and the dumbwaiter. You can see down where they plastered over some of the wall, it used to have a teller window right there open to the tunnels for customers.
Supposedly, you could go from Union Station all the way to the capital building underground (but I doubt that).
I’m sure most of the tunnels aren’t passable, possibly collapsed, filled in, or flooded. But I seriously want to go down and try to map out some of them to be restored like they did in Seattle.
Pretty interesting, looks like Google Elevation API misses some tunnels though (looking at a route that should go through Broadway tunnel right now). Tunnels are key for getting the Flattest Route™.
I think the only time it's moving close to high-rises again is over by the University.
Edit: I believe they went so deep because of the volume of glacial deposits in this area. Otherwise they would have been going through gravel. That made building the stations a bit of a pain (the Beacon Hill station still has chronic problems with water. It smelled like a moldy towel for a long time).
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