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Comment by mc32 | Hacker News Reader

Goodbye "high-rises can't be built in SF because they cast an unsightly shadow". But also hope it doesn't mean California gets to regulate San Jose's "green belt".

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isn't building high-rises in SF precarious because the ground is soft, with inadequate bedrock? are there also concerns about aesthetics, if i understand?

From what I understand it's about the same as building in Tokyo. With modern technology and proper materials you can build a safe building. But the residential tower currently sinking into the ground indicates that either that isn't actually true or the rules aren't being enforced.

Yeah, that one was a case of taking shortcuts. The bedrock was 200"[1] down but the studies they used said that wasn't necessary. So NOW they are taking steps to introduce new pilons that go all the way down to bedrock and will be braced to the current, faultily installed ones.

[1] Not sure the exact depth, but whatever, they went like half way down to save on money.

I think it's more likely that corners were cut with the Millennium Tower, or the engineers made an error of some kind.

None of the other big buildings in SF are connected to the bedrock. None of the towers in LA have supports connected to the bedrock. Heck, the Burj Khalifa isn't connected to bedrock. They all use friction piles, and these can work fine if they're done properly.

> None of the other big buildings in SF are connected to the bedrock

Absolutely not true.

Salesforce Tower, Park Tower and 181 Fremont all being examples of tall buildings in the immediate vicinity that do go to bedrock.

Whether or not friction piles are a good idea is another matter.

friction piles? (trying to look that up)

The top page of Google search results for "friction pile" are all bang on.

thank you

I stand corrected! I got my information from a soil scientist who was explaining that the bedrock wasn't anywhere close to the surface in SF and LA and misunderstood that to mean that none of the towers went all the way down. I stand by my claim that the Burj Khalifa isn't on bedrock, however.

I would expect there to be a viable range of building heights (and building techniques) on the spectrum of single storey house to highrise.

In one notable case, it was decided to not bore all the way down to bedrock, resulting is a sinking building and many lawsuits. More commonly, someone complains that a planned building will cast a shadow, and after spending millions the builders are not allowed to proceed.

The Millenium tower:

https://www.theguardian.com/us-news/2022/jan/10/san-francisc...

https://www.imdb.com/title/tt8105988/

Here is someone who goes into detail about the Millennium Tower debacle: https://www.youtube.com/watch?v=ph9O9yJoeZY

In short, shortcuts, or more charitably, miscalculations. They really thought they had enough margin to work with but obviously that wasn’t the case.

If that were true, there wouldn't be any building in the New Orleans area more than a couple stories high. Everything south of the lake is built on an alluvial delta.

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