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Comment by cobbzilla | Hacker News Reader

it boggles my mind that the developers were not required to sink the foundation piles all the way into bedrock. how unusual is this for tall buildings in the city by the bay? there is so much wealth in SF, this is a luxury tower, it's all a bit strange.

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There are bedrock piles, and there are friction piles. The latter rely on friction of the material they're plunged into to stay put. They are effective and commonly used.

Despite how comforting the word bedrock is to our ears, neither one is "superior" to the other.

Obviously something is going wrong here, but it's not a case of "oh the developers cheaped out and decided to just build a giant skyscraper with no foundation!"

I'm curious: How many other buildings over 20 stories in the SOMA neighborhood use friction piles? Why would anyone use bedrock piles if they are more expensive and have no "superior" advantages? How many buildings with bedrock piles in SF have tilted this much as they have settled in?

I'd say it's less about piles going to bedrock and more about the ground itself.

Building on sand, trash, and whatever other gunk comprises San Francisco ground...

You could say whatever you like, but none of the other tall buildings in SF are sinking noticeably, which suggests your theory may itself lack a solid foundation.

Are the pilings for those other tall buildings in the bedrock?

Depends. Some are but but in recent years it's been more common to use steel structures which (being lighter) don't require that.

Noise might have something to do with too. The last building that I recall having bedrock-depth pilings involved loud shuddering bangs through the financial district for nearly a month. Like you could feel it through the ground 3 blocks away every time they dropped the hammer..

IIRC, a potential confounding factor was that this building is much heavier and has a smaller footprint than standard.

that's why you go down to the bedrock, because the earth in between is not strong/stable enough. also, while much of eastern SOMA is indeed landfill of the bay, this particular building is far enough inland and would be within the original SF coastline.

SF Chronicle had a good overview[0] of what could be going wrong. From the article:

The tower was built using a concrete frame instead of steel. Which is much heavier - it puts about 4.75x the amount of pressure on the soil below the building (as compared to other steel framed buildings of similar size).

It appears that some of the sinking could be due to weight and changing soil composition (less moisture and nearby excavation).

[0] http://www.sfchronicle.com/bayarea/article/Sinking-Millenniu...

I worked in business litigation for a few years and I obviously can't go into any specifics but you'd be shocked/surprised at the number of buildings that the plans say X but somehow Y happened....

Owned a condo. Code and plans said to install a drain clean out in the main sewer line. Cost to builder? Maybe $20. Done wrong and closed up, no one knew so he got away.

Few years later, maybe 10k in damages and 5k to fix. All so the builder could save $20.

Things like this x 100 are everywhere. This is why building codes are nice, although people complain about them.

Even basics like "does the person/company building something own the land it is built on" can go horribly wrong.

Edit: Here in Scotland if someone builds something on your land then it belongs to you and you are under no obligation to warn them of this fact!

Yah there is that. In the US, it is usually mandated that you get something called "title insurance". There are different levels depending who it protects (lender vs buyer). If down the line it turns out you don't own the land your house is on, the title insurance company does lawsuit magic or somehow pays to make the lender whole.

End up costing ?? $1,000 or so per real estate transaction. 99.9999% of the time pays back zero. I suppose nice to have for the last .0001%.

We had to use ours. What happened is that the title people didn't realise the guy selling us the house had two properties and they paid off the wrong house.

Then the guy sold his (newly paid off) house and disappeared.

The first time we leaned anything was amiss was when we had an eviction notice posted on our door. The title company didn't bother telling us until it got that far.

It caused a whole bunch of problems and the company kept dragging their feet hoping someone else would pay. It took a lawyer and threat of a suit to get them to finally pay out.

Codes don't mean squat if the inspector doesn't or won't catch violations on the closeout.

Not sure the value add of that statement.

Clearly some codes do work, and the average building has less issues because of codes.

The value add is saying that codes are important, but enforcement is just as important. Perhaps moreso because if you skip the latter, the former doesn't mean anything at all.

If the builder skimped on the $20 cleanout, it should have been noticed by the building inspector.

I had a friend whose bathtub drain was attached to nothing at all. It just spilled out into the space below the apartment. When they opened out up, they're was a giant subterranean pond hollowed out by years of water pouring out onto the ground.

Shades of Arrested Development.

And the building code means the minimum code required not the maximum. A builder can make it better if they want to when they are building a structure.

I don't know. It sounds bad, but if you aren't a professional engineer lots of stuff sounds bad. "Hang a roadway from cables anchored at the ends? Madness!".

Unless you're a civil engineer, your comment is rather low in information value.

Same here. I like to imagine that this was all the result of a consultation with a tourism consultant from Pisa.

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