7 ms·

In San Francisco, a Sinking Skyscraper and a Deepening Dispute

130 points by BinaryIdiot 10y ago

pstuart 10y ago
It's kind of mind blowing that a building of this magnitude would go in a location that is bay fill in a region renowned for earthquakes, yet not have pilings going down to bedrock. The real aftershocks are going to be the lawsuits over this.
- nashashmi 10y ago
  Unless I am losing my memory, I remember learning in geology class that seismic waves travel the least in clay and most in rock.
  - knorby 10y ago
    Soil liquefaction is the real risk during earthquakes. Clay absorbs the energy and shakes a great deal more, and the soil can potentially destabilize further and allow structures to sink in.
    - wlesieutre 10y ago
      For anyone not familiar, this is an effect where if you load wet soil just right it will break the structure of the soil grains and turn into a fluid. Demo here, you can skip the first minute if you're short on time: https://www.youtube.com/watch?v=-X9-4tWpMCo https://www.youtube.com/watch?v=-X9-4tWpMCo Wikipedia has more information and some good photos: https://en.wikipedia.org/wiki/Soil_liquefaction https://en.wikipedia.org/wiki/Soil_liquefaction It's a really cool and equally terrifying phenomenon if you're used to thinking of the ground as a solid object. Plenty of videos on YouTube as well. EDIT- Here's a car that sunk into the ground, which then resolidified around it: https://youtu.be/2WoKu5VxKgs?t=50 https://youtu.be/2WoKu5VxKgs?t=50 http://izismile.com/2012/08/31/christchurch_liquefaction_26_pics.html http://izismile.com/2012/08/31/christchurch_liquefaction_26_...
- myegorov 10y ago
  Pile foundations are impractical for much of San Francisco founded on bay mud (bedrock hundreds of feet below surface). There're other practical solutions - including soil improvement, micropiles and/or raft foundation - that have been proved capable of supporting highrises. On a different note, a settlement (even differential) in excess of one foot is expected for a significant fraction of building stock in SF in the event of a "design-level" earthquake. The tower is reportedly 6" out of plumb. Over its 600ft height, that's 0.08%. For perspective, it is generally accepted that construction tolerances will result in a building 1/500, or 0.2%, out of plumb at the time of erection.
BinaryIdiot 10y ago
It's leaning 6 inches so I'm assuming it's going to continue to lean further and further each year unless they make modifications to the building (so lopping off the top 20 floors or whatever else that could fix or mitigate it). At which point does it lean far enough that they have to demolish the building? At which point does the entire building become a safety issue should an earthquake (or even "the big one") ever hit? Working in the city these tall buildings going up kinda worry me with the area being prone to earthquakes. I'm not a structural engineer so maybe my worries are misguided but they're there.
- nikmobi 10y ago
  My thoughts as well. Does anyone here have any insight on if it's misguided to worry here? Second, what exactly, if anything, can be done to fix the lean, or prevent it from leaning any further?
  - the_mitsuhiko 10y ago
    Depends on what your worry is. It can lose value. There are many options to keep it straight but they all come with some disadvantages. Worst case you build something next to it and tether them together.
    - mikeryan 10y ago
      You can't really build anything next to that building. It's surrounded on three sides by major thoroughfares and a brand new terminal on the fourth.
- idlewords 10y ago
  Tall buildings built to seismic code are some of the safest structures to be in in an earthquake. Though you'll probably need a change of underwear afterwards: https://www.youtube.com/watch?v=NisWbAXfyWI https://www.youtube.com/watch?v=NisWbAXfyWI
  - BinaryIdiot 10y ago
supahfly_remix 10y ago
Because the building sank 8 inches, did the builder subsequently need to fix they entrance to the building? Does one step down into it from street level?
- BinaryIdiot 10y ago
  So I was wondering this as well. Walking by the building I never noticed. Checking Google Maps Street View I also couldn't tell. So I'm curious how this works. It's sank a total of 16 inches; 8 of which happened after it was completed. So why does it not look funny? Am I thinking about this wrong?
- helper 10y ago
  No. Besides some cracks in the sidewalk you can't tell that it has sunk. (I work across the street from the Millennium Tower).
  - supahfly_remix 10y ago
    Thanks. It must have pulled down the adjacent sidewalk with it, creating a more gradual slope then.
    - kalleboo 10y ago
      That was the conclusion the last time this story came up a month or so ago. They've also been continually re-pouring the sidewalk concrete so you can't see the cracks.
      - newman314 10y ago
        How does this not snap the pipes going in and out of the building?
        anonymfus 10y ago
        Pipes have special joints for thermal expansion compensation.
partycoder 10y ago
Many San Francisco buildings are placed in a zone called the liquefaction zone. There are maps that show which areas will suffer liquefaction in the event of an earthquake.
- Zhenya 10y ago
  Map for reference: https://www.google.com/maps/d/u/0/viewer?mid=19TDkFjIeO9wD5snoxkbMQBjsjUg&hl=en https://www.google.com/maps/d/u/0/viewer?mid=19TDkFjIeO9wD5s...
  - crazy2be 10y ago
    For those curious, this is a (crappier) map of the whole bay: https://commons.wikimedia.org/wiki/File:SFBALiqufactionMap.jpg https://commons.wikimedia.org/wiki/File:SFBALiqufactionMap.j...
    - aristus 10y ago
      Hi-res PDF of that bay map: http://pubs.usgs.gov/of/2000/of00-444/of00-444_8b.pdf http://pubs.usgs.gov/of/2000/of00-444/of00-444_8b.pdf
  - mcguire 10y ago
    Conveniently, the Millennium Tower is in the middle of it.
trhway 10y ago
25 years ago working summer construction projects doing foundations in Siberia we were explained what depth to reach and why (permafrost etc.), and in particular we were taken on a short sightseeing tour of couple of buildings for which it wasn't done properly - the screwed geometry of those buildings one could see with naked eye from distance. I guess that tower in SF will be serving similar educational purpose for decades to come :)
- tinco 10y ago
  In my hometown there is a building that was built in 1529 and leans more than the tower of pisa. It was intended to be taller than our rival cities tower, but it already started sagging during construction. To counteract the sagging the builders actually made kinks in the construction so next layers would be level again, but obviously this didn't help. They never got further than the base of the tower, which still stands and is a fun place to visit. https://en.wikipedia.org/wiki/Oldehove_(tower) https://en.wikipedia.org/wiki/Oldehove_(tower)
rando444 10y ago
This exact same thing is happening in Oslo. All of the new skyscrapers downtown around the opera house are sinking into the ground, and new construction is making the situation worse. Curiously I can't find any articles about this in English, but here is one in Norwegian. http://www.tu.no/artikler/bjorvika-synker/231007 http://www.tu.no/artikler/bjorvika-synker/231007
coldcode 10y ago
I find it amazing that an earthquake prone city had no requirements for building a skyscraper in a reclaimed soil area needing outside verification of the engineering plan.
rwmj 10y ago
Anyone wish to comment on whether "lopping off the top 20 floors" is an even remotely plausible plan? It sounds completely implausible to me, but then I'm not a civil engineer.
- blaze33 10y ago
  Sounds indeed implausible but it has been done before: https://youtu.be/8_4G_8gEjng https://youtu.be/8_4G_8gEjng
  - BinaryIdiot 10y ago
    Okay that is the coolest thing I've seen in a while. I never really thought about how you'd dismantle a building without a single demolition event. I wonder how practical / cost effectice this is in comparison.
VonGuard 10y ago
Last time this was mentioned on HN, someone asked me to go take pictures of the building. I did: https://www.flickr.com/photos/vonguard/albums/72157672701771432 https://www.flickr.com/photos/vonguard/albums/72157672701771... You can see the bowing of rht sidewalk outside, and where the foundation is breaking away from the ground.
VonGuard 10y ago
Last time this was mentioned on HN, someone asked me to go take pictures of the building. I did: https://www.flickr.com/photos/vonguard/albums/72157672701771432 https://www.flickr.com/photos/vonguard/albums/72157672701771... You can see the bowing of rht sidewalk outside, and where the foundation is breaking away from the ground.
jzl 10y ago
A lot more details in this new article: http://www.sfchronicle.com/bayarea/article/Sinking-Millennium-Tower-s-developer-built-9278364.php?t=699cf311b0 http://www.sfchronicle.com/bayarea/article/Sinking-Millenniu... Including comparisons to neighboring buildings with a very well done chart. And this frightening statistic: On Friday the transbay authority released a report by the engineering firm ARUP, showing that the Millennium Tower is four to five times heavier than any other building in the area with a similar foundation, including 100 First St., 199 Fremont St. and 555 Mission St. Building weights are measured in kips — 1,000 pounds — per square inch of pressure on the soil below. The tower at 555 Mission, for example, is 487 feet tall compared with 645 for the Millennium, but it exerts 2.4 kips per square inch while the Millennium exerts 11.4 kips.

130 points by BinaryIdiot 10y ago

It's kind of mind blowing that a building of this magnitude would go in a location that is bay fill in a region renowned for earthquakes, yet not have pilings going down to bedrock. The real aftershocks are going to be the lawsuits over this.

nashashmi 10y ago
Unless I am losing my memory, I remember learning in geology class that seismic waves travel the least in clay and most in rock.
- knorby 10y ago
  Soil liquefaction is the real risk during earthquakes. Clay absorbs the energy and shakes a great deal more, and the soil can potentially destabilize further and allow structures to sink in.
  - wlesieutre 10y ago
    For anyone not familiar, this is an effect where if you load wet soil just right it will break the structure of the soil grains and turn into a fluid. Demo here, you can skip the first minute if you're short on time: https://www.youtube.com/watch?v=-X9-4tWpMCo https://www.youtube.com/watch?v=-X9-4tWpMCo Wikipedia has more information and some good photos: https://en.wikipedia.org/wiki/Soil_liquefaction https://en.wikipedia.org/wiki/Soil_liquefaction It's a really cool and equally terrifying phenomenon if you're used to thinking of the ground as a solid object. Plenty of videos on YouTube as well. EDIT- Here's a car that sunk into the ground, which then resolidified around it: https://youtu.be/2WoKu5VxKgs?t=50 https://youtu.be/2WoKu5VxKgs?t=50 http://izismile.com/2012/08/31/christchurch_liquefaction_26_pics.html http://izismile.com/2012/08/31/christchurch_liquefaction_26_...
myegorov 10y ago
Pile foundations are impractical for much of San Francisco founded on bay mud (bedrock hundreds of feet below surface). There're other practical solutions - including soil improvement, micropiles and/or raft foundation - that have been proved capable of supporting highrises. On a different note, a settlement (even differential) in excess of one foot is expected for a significant fraction of building stock in SF in the event of a "design-level" earthquake. The tower is reportedly 6" out of plumb. Over its 600ft height, that's 0.08%. For perspective, it is generally accepted that construction tolerances will result in a building 1/500, or 0.2%, out of plumb at the time of erection.

BinaryIdiot 10y ago

It's leaning 6 inches so I'm assuming it's going to continue to lean further and further each year unless they make modifications to the building (so lopping off the top 20 floors or whatever else that could fix or mitigate it). At which point does it lean far enough that they have to demolish the building? At which point does the entire building become a safety issue should an earthquake (or even "the big one") ever hit? Working in the city these tall buildings going up kinda worry me with the area being prone to earthquakes. I'm not a structural engineer so maybe my worries are misguided but they're there.

nikmobi 10y ago
My thoughts as well. Does anyone here have any insight on if it's misguided to worry here? Second, what exactly, if anything, can be done to fix the lean, or prevent it from leaning any further?
- the_mitsuhiko 10y ago
  Depends on what your worry is. It can lose value. There are many options to keep it straight but they all come with some disadvantages. Worst case you build something next to it and tether them together.
  - mikeryan 10y ago
    You can't really build anything next to that building. It's surrounded on three sides by major thoroughfares and a brand new terminal on the fourth.
idlewords 10y ago
Tall buildings built to seismic code are some of the safest structures to be in in an earthquake. Though you'll probably need a change of underwear afterwards: https://www.youtube.com/watch?v=NisWbAXfyWI https://www.youtube.com/watch?v=NisWbAXfyWI
- BinaryIdiot 10y ago

supahfly_remix 10y ago

Because the building sank 8 inches, did the builder subsequently need to fix they entrance to the building? Does one step down into it from street level?

BinaryIdiot 10y ago
So I was wondering this as well. Walking by the building I never noticed. Checking Google Maps Street View I also couldn't tell. So I'm curious how this works. It's sank a total of 16 inches; 8 of which happened after it was completed. So why does it not look funny? Am I thinking about this wrong?
helper 10y ago
No. Besides some cracks in the sidewalk you can't tell that it has sunk. (I work across the street from the Millennium Tower).
- supahfly_remix 10y ago
  Thanks. It must have pulled down the adjacent sidewalk with it, creating a more gradual slope then.
  - kalleboo 10y ago
    That was the conclusion the last time this story came up a month or so ago. They've also been continually re-pouring the sidewalk concrete so you can't see the cracks.
    - newman314 10y ago
      How does this not snap the pipes going in and out of the building?
      - anonymfus 10y ago
        Pipes have special joints for thermal expansion compensation.

partycoder 10y ago

Many San Francisco buildings are placed in a zone called the liquefaction zone. There are maps that show which areas will suffer liquefaction in the event of an earthquake.

Zhenya 10y ago
Map for reference: https://www.google.com/maps/d/u/0/viewer?mid=19TDkFjIeO9wD5snoxkbMQBjsjUg&hl=en https://www.google.com/maps/d/u/0/viewer?mid=19TDkFjIeO9wD5s...
- crazy2be 10y ago
  For those curious, this is a (crappier) map of the whole bay: https://commons.wikimedia.org/wiki/File:SFBALiqufactionMap.jpg https://commons.wikimedia.org/wiki/File:SFBALiqufactionMap.j...
  - aristus 10y ago
    Hi-res PDF of that bay map: http://pubs.usgs.gov/of/2000/of00-444/of00-444_8b.pdf http://pubs.usgs.gov/of/2000/of00-444/of00-444_8b.pdf
- mcguire 10y ago
  Conveniently, the Millennium Tower is in the middle of it.

trhway 10y ago

25 years ago working summer construction projects doing foundations in Siberia we were explained what depth to reach and why (permafrost etc.), and in particular we were taken on a short sightseeing tour of couple of buildings for which it wasn't done properly - the screwed geometry of those buildings one could see with naked eye from distance. I guess that tower in SF will be serving similar educational purpose for decades to come :)

tinco 10y ago
In my hometown there is a building that was built in 1529 and leans more than the tower of pisa. It was intended to be taller than our rival cities tower, but it already started sagging during construction. To counteract the sagging the builders actually made kinks in the construction so next layers would be level again, but obviously this didn't help. They never got further than the base of the tower, which still stands and is a fun place to visit. https://en.wikipedia.org/wiki/Oldehove_(tower) https://en.wikipedia.org/wiki/Oldehove_(tower)

rando444 10y ago

This exact same thing is happening in Oslo. All of the new skyscrapers downtown around the opera house are sinking into the ground, and new construction is making the situation worse. Curiously I can't find any articles about this in English, but here is one in Norwegian. http://www.tu.no/artikler/bjorvika-synker/231007 http://www.tu.no/artikler/bjorvika-synker/231007

coldcode 10y ago

I find it amazing that an earthquake prone city had no requirements for building a skyscraper in a reclaimed soil area needing outside verification of the engineering plan.

rwmj 10y ago

Anyone wish to comment on whether "lopping off the top 20 floors" is an even remotely plausible plan? It sounds completely implausible to me, but then I'm not a civil engineer.

blaze33 10y ago
Sounds indeed implausible but it has been done before: https://youtu.be/8_4G_8gEjng https://youtu.be/8_4G_8gEjng
- BinaryIdiot 10y ago
  Okay that is the coolest thing I've seen in a while. I never really thought about how you'd dismantle a building without a single demolition event. I wonder how practical / cost effectice this is in comparison.

VonGuard 10y ago

Last time this was mentioned on HN, someone asked me to go take pictures of the building. I did: https://www.flickr.com/photos/vonguard/albums/72157672701771432 https://www.flickr.com/photos/vonguard/albums/72157672701771... You can see the bowing of rht sidewalk outside, and where the foundation is breaking away from the ground.

VonGuard 10y ago

jzl 10y ago

A lot more details in this new article: http://www.sfchronicle.com/bayarea/article/Sinking-Millennium-Tower-s-developer-built-9278364.php?t=699cf311b0 http://www.sfchronicle.com/bayarea/article/Sinking-Millenniu... Including comparisons to neighboring buildings with a very well done chart. And this frightening statistic: On Friday the transbay authority released a report by the engineering firm ARUP, showing that the Millennium Tower is four to five times heavier than any other building in the area with a similar foundation, including 100 First St., 199 Fremont St. and 555 Mission St. Building weights are measured in kips — 1,000 pounds — per square inch of pressure on the soil below. The tower at 555 Mission, for example, is 487 feet tall compared with 645 for the Millennium, but it exerts 2.4 kips per square inch while the Millennium exerts 11.4 kips.