...2 inches for such a tall building is such tiny angle
If it sinks does this mean the first floor is slightly below the street level ..it probably means that the areas around the door and where the concete meets the street are cracked
Millennium Tower is tilting, sinking
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Re: Millennium Tower is tilting, sinking
#12What is the risk? Does this make the building more dangerous because it's in an earthquake-prone area? Obviously this doesn't sound good, but the article mentions that there is no threat to safety of occupants. Is it merely aesthetic?
Uneven sinking is not good - doors/windows won't close, walls would crack, and so on. It does not take much to seize things, however buildings are usually designed to take a little of it. The rate at which it's sinking is the alarming part.
But i would be mostly alarmed about earthquakes - the thing sits on sand. Proverbial or not, that would make it very susceptible to soil liquification.
Imagine a stick with a weight on top of it. On solid ground it stands still. But if the ground was to turn into a liquid, the stick would tilt and sink rapidly. If the soil were to liquify for a second, it would end up at an angle half-sunk. And a building can't tolerate side loads, so it won't stay at an angle - it would collapse down.
Re: Millennium Tower is tilting, sinking
#13"To cut costs, Millennium did not drill piles to bedrock." What are the implications for earthquake safety?
I'm sure the engineers ran the calculations and deemed it 'safe enough'
Re: Millennium Tower is tilting, sinking
#14Earlier quoted context omitted.
Probably not good. According to this and other articles, the building's concrete slab foundation sits roughly 80 ft below street level upon sand, while bedrock lies 200 ft down. That means there is 120 ft of sand, possibly susceptible to liquefaction, between the buildings foundation and solid bedrock. That sounds bad enough. But now imagine the building is tipping over slightly. The already potentially worrisome pro…
How much would it have cost to dig down to bedrock, and pour a concrete foundation from the bedrock up to surface level? Between the amount of sand to be moved and the amount of concrete to be poured, it sounds like an enormous fortune; I guess that the relevant questions are whether the market could bear it and whether it would be cheaper than the rapidly-developing lawsuits. It may be that the building didn't make…
The real problem with digging down to bedrock is destablizing the building. Though there may be enough redundancy in the pilings to do it one at a time.
Re: Millennium Tower is tilting, sinking
#15"To cut costs, Millennium did not drill piles to bedrock." What are the implications for earthquake safety?
Not a geologist, but I suspect that'll depend on how liquid the 120' of sand between the piles and the bedrock gets.
Re: Millennium Tower is tilting, sinking
#16My house is on a steep hill, and Seattle has a reputation for hills sliding away under heavy rain. Before building it, I hired 3 separate geologists to evaluate the site. After digging holes, they said the site was sitting on "glacial till", which is clay that was compacted by about a mile of ice, and said there was nothing to worry about. Paying them was worth it for the peace of mind. (Turns out the till was so har…
Building a large edifice on sand? Put that starkly, I could swear that I heard a story about it once. No idea where, though. ;)
Re: Millennium Tower is tilting, sinking
#17The article doesn't talk about the how this practically affects the entrances to the building. Do the doors have to be adjusted for such a drastic sinkage, or are buildings somehow designed so this isn't noticeable to the public?
Re: Millennium Tower is tilting, sinking
#18My house is on a steep hill, and Seattle has a reputation for hills sliding away under heavy rain. Before building it, I hired 3 separate geologists to evaluate the site. After digging holes, they said the site was sitting on "glacial till", which is clay that was compacted by about a mile of ice, and said there was nothing to worry about. Paying them was worth it for the peace of mind. (Turns out the till was so har…
One of the geologists told me a simple way to judge the slide risk. Look at the tree trunks. If tree trunks are leaning, or are curved, that indicates the ground under them is shifting.
Re: Millennium Tower is tilting, sinking
#19From the article: "To cut costs, Millennium did not drill piles to bedrock."
I'm amazed that a building of that height would be built on a slab with friction piles in the mudflat fill zone of the SF bay. How did they get a building permit for that? 16 inches of sinkage in 8 years is huge.
Building sinkage isn't all that unusual, but not for skyscrapers. There was a time when skyscrapers were only built on competent rock, like NYC's. Now they're being built on much more iffy soils. Singapore and some other coastal Asian cities are doing a lot of this.
SF used to be smaller. The outer half mile or so on the bay side is fill. There are buried shipwrecks all through that area.[1]
[1] https://medium.com/the-secret-history-of-america/from-starbo...
Re: Millennium Tower is tilting, sinking
#20My house is on a steep hill, and Seattle has a reputation for hills sliding away under heavy rain. Before building it, I hired 3 separate geologists to evaluate the site. After digging holes, they said the site was sitting on "glacial till", which is clay that was compacted by about a mile of ice, and said there was nothing to worry about. Paying them was worth it for the peace of mind. (Turns out the till was so har…
Loving your attitude.
I often feel like with a lot of building (big and small) there is insufficient evaluation of site factors. For example:
Is there a hill above the site? THAT needs to be evaluated (sometimes they do, sometimes they don't).
Is the site on a traditional floodplain? If so what actions have been taken to redirect the water flow? Does the system have the capacity to move the water away?
Is the site itself earthquake proof (e.g. subject to severe liquefaction)? Just because the property is built to code, doesn't mean the land it is built on is safe.
Is the site subject to wildfire risk? Can we mitigate that?
Humans make the same mistakes again and again. We build fast and we don't consider the land's natural problems. INstead we just build and hope it happens far enough in the future for it to be someone else's problem.
Water in particular we're TERRIBLE at managing. We build property on floodplains and are then "surprised" when it floods. We place homes on downward elevations and don't redirect the water around the property (e.g. using french drains).