My 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 hard it could not be dug with hand tools.)
I did have a scare because a spring appeared on the edge of the property, as underground water is indicative of slide risk. Fortunately, it turned out to be a leak in the water main!
I still made sure the hard surfaces all drained into the storm drain, so that the hill wouldn't become saturated with water.
I can't conceive of building a 58 story building on sand in an earthquake zone. Reminds me of that Monty Python quote:
"When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built in all the same, just to show them. It sank into the swamp. So I built a second one. That sank into the swamp. So I built a third. That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Lad, the strongest castle in all of England."
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).
I did a lot of things to reduce risk. None were expensive. I watch other houses go up in the neighborhood, and they do none of them.
My most expensive mistake was not having a geothermal heading system installed when the yard was all dug up anyway. I could have had it essentially for free, and save 30% on the heating bill.
What type of system were you evaluating? I'm not sure why this isn't a common feature in homes, as I've only seen it done on more industrial scales (e.g. mid-sized condos).
I have only installed one, and I can't comment on how effective it is at reducing cooling costs as it's a new home (though I lived there for a couple of weeks before I got the heat pump units). But I can comment on the "why not".
Generally it's very expensive to install because it requires several thousand feet of underground pipe to normalize the temperature of the water going through the system. Many homes don't really have enough land to support this horizontally. You can install the loop vertically (like a drilled well), which is again, pretty expensive up front. Few take the long view.
I happen to have plenty of land and a backhoe so I just dug a ditch.
Watching videos of the aftermath of the floods in Maryland the other day was telling - the main street had been entirely washed away, exposing the foundations of the buildings. The modern constructions essentially had none and were hanging in mid-air over voids. The older buildings were all sat upon massive and well dressed masonry.
In short, people account only for risks they have experienced firsthand. When you don't see flash floods or earthquakes for generations, you get lax. Sadly we tend to wait until after disasters to learn, and yet we still forget.
Tangentially related, I have a chum who used to work for the UK's Environment Agency.
As some may have noticed, the UK seems to be suffering flooding more than it used to. Part of his job was to speak at town halls and village church halls and the like during and after flooding. He'd take a backup man with him whose job was to sit in the car outside with the engine running.
So he'd turn up at a newly built settlement named "Little Flodington" or some other such. He'd look at the unforgiving rocky hills surrounding it, and at the river running through the middle of it. He'd check the history to find that for the last thousand years, the only recorded usage of the land was grazing animals and growing crops that can handle a lot of water. No buildings more elaborate than temporary shepherd huts. He'd open up the department's flood-risk maps from the last fifty years and find he was standing in the middle of a big blue section.
He'd then field questions along the lines of "Why didn't you stop my house being flooded?" and "How are you going to stop it happening again?" with answers that were not well-received. "You bought a new house on a flood-plain. We're not going to stop it happening again."
He's since moved on up to work for a local council's environment dept. A council with less flooding.
Growing up in London, I remember reading at a young and impressionable age the sage advice to never buy property built on streets called Marsh Lane, and similar, so it's not a new problem. Geography would be a lot more interesting as a school subject if they taught this kind of stuff - although I rather fear for the results when the kids got home to explain it all to their parents.
I live in the Outer Richmond district of San Francisco, which was built on sand dunes. Most houses in my neighborhood were built in the 1920s and 1930s, +/- a decade.
I was told by a contractor that it's extremely common for houses to have shifted considerably, sometimes by several feet. Mine certainly has, though not nearly that bad.
Most of the houses are built on concrete foundation walls that go about 3 feet into the sand. Despite being unreinforced and using water-permeable cement, they've seemed to hold up reasonably well. It's usually the whole house that shifts and racks. Yet looking from the street you wouldn't expect that because all the houses abut each other, with only a few inches or none of space in-between. (Perhaps this has mitigated the problem somewhat, though.)
Despite being built entirely on giant sand dunes, the Richmond district is only "moderately" prone to liquefaction. And there wasn't much notable damage during the 1989 earthquake, AFAIK. I think (though cannot confirm) that similar foundation techniques were used as far back as 1905 and earlier, in the Richmond, Sunset, and elsewhere, and judging by their survival and continued use of the foundation techniques I'm not particularly worried. (While widespread building in the western half of the city didn't begin in earnest until about 1910'ish, there are hundreds of buildings many decades older randomly distributed, especially closer to the beaches.)
The bigger problem is that almost all houses in the western half of the city were built with so-called soft stories as the first floor--basically a giant open space supported almost entirely by the external walls. Interestingly, AFAIK this design came before the widespread introduction of cars. These days nearly all houses use that space as a garage, but I believe they were built as unfinished first floors intended to be finished as desired--e.g. workshop, additional family rooms, in-law apartments, etc--while keeping the initial purchase price low.
If it's the earth below houses also moving, then the problems in plumbing and electricity do not appear at the house; they appear at the cross section of the moving and non-moving earth masses, and are typically the responsibility of utility provider.
For plumbing, I don't know. That's a good question I should ask a contractor the next time it comes up. But given how old these houses are perhaps the problems are sporadic. A broken pipe here or there gets fixed and people move on. And some kinds of movement might not matter, like if the back of the houses shifts down the front end might not move nearly as much.
Also, AFAICT the plumbing comes up under the foundation walls, not through. Concrete slabs on the first floor aren't original (and you can still find the occasional house with a dirt floor at the first level), so maybe there are some degrees of freedom of movement that mitigate problems.
For electricity the Richmond and Sunset districts and I believe the vast majority of the city uses overheard wires. So there's plenty of slack.
I lived in SF's Inner Sunset for several years. When the old DeYoung museum was demolished and all the landscaping scraped away, the "soil" underneath was pure sand.
I noticed the same thing at my home a few blocks away -- the city had to dig a trench in the street and after they got down a few feet, there was no soil, just beautiful beach sand. A little disconcerting with SF's earthquake history.
"In Paris, the famous phrase Sous les pavés, la plage! ("under the cobblestones, the beach") was used by the May 1968 protesters to mean that it was possible to escape from a regimented life."
Only those buildings with 5 or more units, which is only a tiny fraction of the structures. Ideally it should be every building, but it's ridiculously expensive to install moment frames, which is pretty much what every house needs given the typical layout of the houses. Each installation costs between $30k to $50k, and as well-off as you need to be to afford to purchase in San Francisco, that's still an expense few can justify even if they could afford it.
We had structural plywood sheathing installed in our garage, and the typical job is around $10k. The pre-existing sheathing was installed by [presumably] a fly-by-night contractor shortly after the 1989 earthquake. Fortunately I noticed that it wasn't installed correctly and used the wrong materials, and so it was basically useless. But given that the garage door, garage side entrance, and entryway make up greater than 80% of the front wall of our first story, that we have a big window and door on the back wall, there's not much room for sheathing (properly installed or not) to control movement along that axis. The house is now very unlikely to collapse into the street, but we're still lucky to be sandwiched between two other houses. Fortunately, our neighbor on the corner had his foundation rebuilt and a third structural wall installed. I should probably be remunerating him somehow.
The fact that they're not able to pass 100% of the cost of whatever capital improvements they feel like on to their renters is part of a massive wealth transfer from landlords to long-established tenants.
In other circumstances I'd accuse that of deterring investment and being a contributor to the terrible housing situation in the Bay Area in general, but honestly, the zoning / planning-permit situation is the first limiting factor.
Instead of "massive wealth transfer", I think you meant to write "slight dent in disgustingly fat profit margins", because - just based on aggregate metrics - most landlords are making a stone-cold killing in this market.
Indeed, let's all shed a tear for the SF landlord. I don't know how those poor folks can stay in business when property taxes are capped and median rent rises at ten times the rate of inflation!
Individual landlords don't see (real) rent increases for apartments are all subject to rent control. They only get an incremental adjustment for inflation. If a landlord owns an apartment but it is occupied by a tenant under rent control, it doesn't matter if the property is "worth" 10x as much. His rent collected hasn't gone up, and he can't sell it for 10x as much because that tenant has very strong legal protections around his use of the property at its price. In that case, 90% of the property's annual returns is being enjoyed by the tenant for as long as he stays there. (He may be able to realize a gain after the tenant moves away or dies, but he's still lost out on the decades of rent which he would have been able to get at market rates.)
Considering that any landlord buying a property will certainly be on the hook for the downside in a property if the housing market crashed, and you'll see that this isn't the greatest. (BUT THE HOUSING MARKET ONLY GOES UP AND WILL NEVER CRASH hahahahahaha yeah right).
Anyway. In general one needn't shed a tear for landlords and capitalists of their ilk for failure to make a profit: the money is its own reward. But we do need to respect the money (because that is the reward), the precise behaviors we are incentivizing, and the impact of political risk which we are inflict upon the people we might want to spend money investing in the region. For instance: making things like this risky means that risk-tolerant entities are likely to be involved (which means the rich guys, speculators and businesses that San Francisco loves, not individual homeowners). And the price of the landlord assuming any political risk will find itself baked into the price of any new rental property.
But as I was saying: it's kinda moot from a median-apartment-price perspective if nothing new gets built anyway for other reasons.
Clearly, you have not heard of "rent control". I know people paying $1200/month for a 2BR in the heart of the City. I even met a guy who was paying $350 for a 1BR in Nob Hill, not far from Grace Cathedral.
About 72% of SF's units are under rent control. So not all landlords are making "fat profit margins".
I didn't say anything about zero risk. As the sibling comment indicates, if the cost is too high tenants will refuse to pay it by not renting the place. How long it takes the landlord to recoup the costs will depend on the local market for rentals.
Landlords may be the only group outside of government who is notorious for always going with the lowest bidder for jobs. A landlord who doesn't shop around for everything isn't going to be in the real estate business for very long.
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.
I've seen fields of trees that have been clearly bent by the wind, they look different than ones from shifting ground. For one thing, there tend to be more branches on the downwind side.
One other thing to look at is fence lines. If you line up a old fence line by eye and look down the line you can see quite small ground shifts. If you do use this make sure you crosscheck with other fences close by to make sure that any deviations are not just due to incompetent fencing.
A friend of mine lives opposite some farmland. He told me the story of the owner of the farmland wanting to sell it for housing. He got a geologist in, who looked at the land and explained that this land was prime for a major landslide because of hollow pockets under the surface.
The farmer thanked the geologist, paid him, and then got another geologist in. This second geologist gave him the all clear that he was paid for, and went on his way.
I should point out that my friend lives on the DOWNHILL side of this land, so when it goes...
I recall a Sunday School song to that effect, with hand gestures. "Theeeeeeeeee foolish man built his house upon the sand, the foolish man built his house upon the sand..."
I really hope the SF rules for building giant buildings are similar to recent Japan ones.
What I've heard is that after the Kobe earthquake, Japanese earthquake rules have been made so good that anything built after '95 has never fallen over, even in 2011-sized earthquakes (at least until the tsunami came).
California seismic building codes are pretty solid. The state does its own earthquake research and has definitely lead the US in terms of building codes. In the US, CA's seismic exam for structural engineers is considered the most rigorous in the country. Generally, the seismic codes are roughly at Japanese levels.
There have been several large M7+ earthquakes in populated areas since the Hanshin (Kobe) earthquake. Tohoku was obviously the biggest. Several of the Tohoku aftershocks were over M7. This spring there was a M7 earthquake in Kumamoto, which I think is the largest earthquake in a very populated area since 2011.
Japan get several very large earthquakes every year, but they are usually in less populated areas. It's quite common to get M6+ earthquakes in populated areas, though. As the GP notes, damage is usually amazingly limited. I experienced one and was very surprised that nothing was damaged in my house.
http://www.jma.go.jp/en/quake/ is super interesting to look at because you get a real sense of just how often Japan is hit with earthquakes (several a day!).
https://www.geonet.org.nz/quakes/felt is the same for New Zealand... there's a moderate or strong quake every couple of weeks, and little ones all the time
I, for one, would rather be building on sand rather than clay. Clay is an absolutely terrible substrate for construction. Not to mention it does not drain. Hills don't become saturated with water... the water tends to flow to ze bottom of ze hill, where it will saturate things. I'd be curious to know what exactly you are draining into... drywells and clay are not friends.
It drains into the storm drains, and the pipes carry that off to wherever they go :-) which is the waterways. I know that because the code people had me build a grass swale to filter the runoff from the driveway before it entered the drain.
Some other homes on the hill had to be built on pilings because they were in an area which was loose dirt that had eroded away from higher up.
I'm not sure if 'clay' is the right word, I don't know much about geology, but the geologist definitely said compacted "glacial till" which he said was ideal.
Haven't had any settling problems so far despite an earthquake and lots of rain.
I passed on another lot where the geologist said the whole hill was going to slide away at some point. The seller didn't want to hear that.
Clay can be a total pain in the ass to work with, it's more stubborn than concrete to remove, but you'd be hard pressed to find a material more solid to build on than rock. What's your beef with clay?
The kind of glacial packed clay mentioned in this article is the sort of stuff even a power shovel has trouble with. It looks like light coloured slate, dry, brittle, and dense.
I'm not sure what your preference for sand is other than it's easy to work with. That stuff can shift, it bloats when wet and heaves with frost, settles like crazy under pressure. Sure, it's easy to remove, but it's so variable I have no idea how you'd get anything to stay level on top of it.
> Sure, it's easy to remove, but it's so variable I have no idea how you'd get anything to stay level on top of it.
Living somewhere built on what is apparently some of the most variable types of clay and that experiences temperature swings of ~150F throughout the year: we don't.
Any basement more than 30 years old is cracked and heaved. Houses require constant adjustment of the teleposts to avoid large cracks forming in the house built on top of the foundation.
>I can't conceive of building a 58 story building on sand in an earthquake zone
There are ~ 8 stories of concrete underground that is is built on. It would be another ~12 stories worth to get down to bedrock. Someone screwed up here but there are plenty of buildings that don't go all the way down to bedrock and are just fine. Maybe if they would have went with a lighter steel frame construction instead of concrete or if the building wasn't so tall the foundation would be fine.
From 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]
How did it get approved? The developer's lobbyist and PR rep is former mayor Brown's spokesman and personal friend, and at the time the current mayor was Newsom, a product of Brown's machine. Newsom was a bit of a crook in the area of real estate, having some self-dealing while he was on the board of supervisors and making sure all of his friends' problems got cleared.
The same lobbyist also represents the Warriors in their current Mission Bay proposal.
Nobody in SFgov is qualified to review the design of a skyscraper's foundation. That is why everyone involved in the project (city building inspectors, investors, lenders, etc) relie on expert engineering firms. Any firm making a mistake of this magnitude - if it is an engineering error - will be out of business and there insurers writing big checks.
While I agree Brown/Newsome/SFGov is shady but I highly doubt they are responsible for this problem. How did they fool the lenders? How did they get multiple engineering firms to sign off? Why would an investor like Millineum Partners want to take such a big risk in an area they have no advantage?
From the article too: "-the famed Petronas Twin Towers in Malaysia, for example, sank only a half inch since opening in 1998-"
I have worked and lived in SE Asia for 8 years, and I can tell you that there are always problems like this when they fail to go deep enough on the piles.
I have also been reading up on the shorter-than-expected life expectancy of iron rebar in concrete construction. They were supposed to be good for 100 - 1000 years. Now, there are studies saying remedial works will probably be needed in 20 to 75 years!
I wouldn't buy into a building that sank so much so rapidly, is tilting too, and is in a seismic zone like SF. Steel would be better to fight the bending due to tilt. Concrete is good for compressive loading mainly, not bending or shear. I hope they used some sort of non-ferrous reinforcement like fibers or mesh.
On every job I have worked on, we always recommend a survey of the structure for up to 2 years each month. When settling seems to level off after initial construction for 4 months straight, it is passed to the owner to maintain a survey at their discretion.
I am used to seeing 2 inches per year on new construction, but I am amazed the Petronas Towers only have sunk a half inch.
Most of our big coastal cities are like that. Boston is about twice as big as it was in colonial times; all of the Back Bay is landfill. A lot of Cambridge is landfill. And yes, most of the taller buildings cluster around the more solid bedrock areas closer to downtown.
But the engineering principles needed here aren't unknown--cities like Las Vegas and New Orleans have modern buildings that are much taller than were thought possible in earlier times. If the developers didn't do it right because it was expensive, then it is on them.
To add on, Chicago and New Orleans are both built on swamps, and the outer edges of New York are filled in -- making land for cities isn't the issue with the tower.
The tallest buildings in Chicago have foundations drilled down to bedrock. The Sears Tower (now Willits Tower) is built on bedrock. The Trump Tower [1] has pilings down to bedrock. The John Hancock building has foundations down to bedrock, even though they had to go down almost 200 feet.[2]
How unusual is 83 floors in earthquake country without foundations down to bedrock?
As an aside, the land in New Orleans is so flat that the zoo has a 28' hill donated by a benefactor, "so that the children of New Orleans can know what a hill is like" according to the plaque next to it. And when I visited, the kids were going nuts over this little hillock, running up and careening down it, giggling.
As a kid I always wondered why so many of the taller buildings clustered up near DTX and then down that little strip down Boylston. As I got a bit earlier and learned what Boston originally looked like, it all made sense.
Of course, all of this landfill area is going to be the first to go back into the sea when the water rises. I figure our house is going to be riverfront property some day.
Years ago I was working for the final company to own the project for Trump Tower Tampa. The reason it didn't get built? It was to be built right next to the river. After the initial site survey the geologist weren't comfortable with the original shoring design, thus they drilled more, and still weren't comfortable. Somewhere along the line the rights to the project were sold off and the incredibly small company I worked for ended up with the rights to the project, which was eventually scrapped. Had the housing boom continued for much longer, I'm afraid it likely would have been built.
It is important to note that one of the chief advantages of building a skyscraper in NYC is that bedrock is within 40 feet of the surface in the downtown district. In other areas of NYC, it is 160 feet to 200 feet below the surface.
Am I reading that map right? Looks like the Millenium Tower is not in the fill zone on the shipwreck map? Hard to tell the shipwreck map looks a bit notional.
Not only did the architect miscalculate the worst-case wind load on the building but the builder substituted cheaper bolted steel connections for the originally-specified fully welded connections.
The problem was remediated by heavily reinforcing the connections of the diagonal steel braces in the frame of the building, but until it was done there was a very real chance of the building blowing over.
It was hurricane season and the repairs were done as a major storm was approaching.
> Three Meteorological experts were retained to provide updates three times throughout a day. An emergency evacuation plan was developed in conjunction with local law enforcement, search and rescue, firefighters, major city authority figures, and shelters. 2000 emergency red cross workers were kept on stand-by in the event of a failure.
In contrast, the Salesforce tower under construction at 415 Mission Street is built on piles that connect to bedrock.
> In a big earthquake, the ground is actually trying to slip sideways underneath the building. “You need something to keep you from changing addresses,” says Joseph. Those somethings are called piles, in essence underground stilts connecting the building with the bedrock. In the lowlands of San Francisco’s Financial District, bedrock is 300 below street level. “We have 42 piles that go all the way down and are socketed 15 to 25 foot deep into the rock,” says Tymoff.
And this was part of the proposal from the very beginning.
> The Transit Tower would have a concrete slab foundation supported by driven piles anticipated to be
founded on bedrock more than 200 feet below grade. The tower’s structural system is anticipated to
employ the concept of “megacolumns,” which are very large structural columns several feet in width.
The concentrated load supported by these megacolumns would be sustained by large diameter piles
approximately 10 feet in diameter, with additional piles driven to support the building’s foundation slab.
FWIW building on sand isn't all that bad if you design the building expecting it to be on sand. The Nazis build AA defenses on sand because a concrete building that's sandwiched between the recoil of small artillery and bedrock won't be around very long. The sand acts like a damper. It's harder to break a cinder block with a hammer if the block is sitting on a pile of sand than if it's on a paved surface and you can apply the same principal at scale if you've got the resources to do all the prerequisite work.
It's not that exotic of a design when you consider that the ground under California tends to move around. Too bad it doesn't look like this building was meant to support itself atop a less than solid underlayment. Too bad for the developers.\s If they have to take corrective action they only get a crazy profit margin instead of an insane one. Should have done it right the first time.
Investors will always want things cheaper, and they don't understand engineering. The responsibility of ensuring that the design is safe falls on the engineer who stamped the drawing. Situations like this are covered in engineering ethics classes, which most civil engineers in the US would have taken.
Plus, depending on the state, a Professional Engineer (a certification earned) has to sign off on this stuff and is liable in the event of something catastrophic happening, like the building falling over.
Because Millennium is on reclaimed land, they cannot determine whether or not they have drilled into bedrock. They drill into what's called the 'point of refusal'; a point where they can no longer drill deeper. Whether this is bedrock or even stable soil is somewhat vague.
- You CAN determine the type of rock you are drilling through as well as it's relevant characteristics. Pieces of the material are brought to the surface with the drilling mud and instruments are put down the hole.
- Builders DO NOT just stop drilling when their drill won't drill no further. (This made me laugh!) There is testing, design, design review, more testing during construction, more design review and perhaps modification based on conditions. If a particular drill could not drill to design depth, they would likely change the bit or drill.
- While there will always be some uncertainty, engineers require more than a vague understanding of soil conditions to design the foundation of a building like this. Any remaining uncertainty should be taken into account in the design.
Maybe I have a poor definition of 'point of refusal', but this is the term developers use. Most developers in SF don't tell you whether they drilled down to bedrock or not.
It's awfully hard to believe that they literally can't tell what the soil is like at the point of refusal. Sending down a camera and a light is child's play compared to actually running a drill string.
to quote Stewart Lee: "as a piece of architecture, that is abysmal. But as an extremely heavy-handed satire of exactly where we're going wrong, superb."
...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
I was wondering the same thing, but Google street view (taken in 2014) doesn't show any evidence of such a big dip. How is that possible?? The only thing I can think of is that it's more of a "sag," where the middle has sunk 18" but the edges haven't moved much, but I'm not really satisfied with that theory.
It's extremely unlikely that the building is sinking and the surrounding area is stable. More likely the building is pulling the entire area down, so it's probably hard to detect as a pedestrian.
Given the choice between two identical apartments in two buildings, one of which is rated "safe" but is tilting, you'd prefer the non-tilting one. I definitely would. Bollocks to the safety rating, I want my building straight and not sinking, please!
This brings me back to a question I have frequently asked myself: What do you do with unsafe or old skyscrapers? How would you raze such a thing? What if it falls over, breaks apart or breaks in on itself (9/11 gives an idea)?
To a layman (with slight acrophobia) skyscrapers seem pretty fragile, and I'd much rather have them built into the ground than towards the sky, but obviously they're holding up in general and I'm interested to see what happens with this one: Hope that it stops tilting or sinking? Raze it before anything bad happens?
Wonderful! Thanks for sharing that. I work in the steel construction industry, we put buildings up all day every day, so watching them come down always interests me.
As a fellow layman I imagine that's where incredibly skilled demolition work comes in. There are some wonderful videos of very precise building demolitions out there.
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 problem compounds dramatically.
The SF Chronicle article that this Curbed article seems to be sourced from provides more information on this.
And while Stanford’s Deierlein doesn’t consider the sink or tilt a safety issue,
he did say, “I would be concerned for my investment.” That’s because a shifting
building can cause walls to crack, elevators to malfunction and all manner of
other annoyances.
P.J. Johnston, spokesman for tower builder Millennium Partners and its principal
owner, Sean Jeffries, said a nine-month, independent structural safety review in
2014 “determined the settlement has not significantly affected the seismic
performance of the building, and does not represent a safety risk.”
The first guy is "Professor Greg Deierlein, director of the John A. Blume Earthquake Engineering Center at Stanford University".
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 economic sense in the first place, if it couldn't be built both safely and profitably -- which has unpleasant implications for the SF housing crunch...
Update: I hadn't known that the usual practice was to build a foundation down to normal depth for a foundation, then set up (large numbers of) pilings from the foundation down to bedrock. That makes sense.
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.
I thought concrete buildings without steel frames came down instantly in earthquakes. What am I missing?
Concrete buildings without sufficient bracing at the corners where supporting beams meet floors fail pretty much instantly in earthquakes for sure, but if you put bracing supports in at the corners then that makes them much, much stronger. You’re probably thinking that concrete buildings just collapse from your experience of post-earthquake film footage from countries with poor governance where building firms can cheap out on the construction (lets save 15% of our material costs by skipping the bracing!) and their buildings inevitably collapse when the next earthquake comes along.
> "The Millennium’s engineers anchored the building over a thick concrete slab with piles driven roughly 80 feet into dense sand. "To cut costs, Millennium did not drill piles to bedrock,"...
They built a skyscraper, on sand, in an earthquake zone!!! What the heck were they thinking?
Consider me completely unsurprised that the building is sinking and tilting.
What 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.
> And while Stanford’s Deierlein doesn’t consider the sink or tilt a safety issue, he did say, “I would be concerned for my investment.” That’s because a shifting building can cause walls to crack, elevators to malfunction and all manner of other annoyances.
How much stock should one put in that declaration of safety? It is from an "independent" analysis... but who paid the analysts? Or, suppose absolute freedom from bias... how many times have expert opinions of safety been wrong in the face of mother nature. Picture Fukushima.
The risks in a tilting building are many. From a market value standpoint, homeowner value has already been destroyed simply by perception. If remediation is necessary here, homeowner fees could dramatically increase. Tilting buildings often see cracks in walls, malfunctioning elevators and other ills which also lower value. There will be lawsuits here-- you can see all sides rattling sabers with legalistic language and positioning already just from these articles -- and those will carry costs as well. Taxpayers may well be pulled into the fray and suffer as well in these situations.
From a pure safety standpoint, experience dictates that we should discount expert declarations of safety in many such matters. Residents of the tower and the towers' neighbors may do well to heed caution. At the end of the day, it is hubris to expect to predict with any high degree of confidence what might happen here. After all, none of the experts from any side involved foresaw even the current predicament, where no grand act of nature is even involved. The building simply stands there, yet already reacts in unpredicted ways. How likely are the experts then to foresee predicaments in even more complex situations?
Yes, that for sure is mentioned as a distinct possibility. Sometimes in such matters the city can also be sued for approving plans if they are subsequently found to be faulty or inadequate as well. And if there is any other construction going on nearby besides this Transbay Terminal that was mentioned, that could be called into question as well.
Dense clay might be unyielding, but depending on the plasticity of that clay you could be facing serious issues with heaving when the soil gets extremely moist.
Surely, the tilting is the biggest worry. Anybody care to estimate how many more inches can this tall building tilt before the lateral stresses lead to its collapse?
There is no scenario in which a 350 million dollar skyscraper deemed "not a safety issue for residents" will be torn down so they can "try again". They'll find a way to stabilize it and that will be that. No one is going to tear down nearly half a billion dollars worth of skyscraper if there's any chance of salvaging it.
Plus if it turns out to have been caused by the Trans Bay Terminal, they have very deep pockets (they supposedly spent $58 million on a buttress to protect the Millineum Tower). As does the developer, Millennium Partners and the engineering from firm's insurance companies.
This will get fixed. There will just have to be a big fight to see who has to pay.
- Foundations of tall building must go to bedrock - not true.
- Large buildings settling is unusual - not true.
- Earthquake safety has been compromised in this case - not true.
The structural engineering of tall buildings is complex. Multiple large engineering firms were involved in the design and construction of this building.
Curbed (owned by Vox BTW) took the SF Cronicle article and cut out the more reasonable paragraphs (such as that same Stanford they quoted saying he "doesn’t consider the sink or tilt a safety issue".).. And of course the Chron article already probably skewed it to make it more exciting.
I always shake my head when I read article on a subject that I happen to be be an expert. I'm sure experts in the engineering of these sorts of projects could teach us alot about this situation.
It seems that you need to read more carefully and perhaps with more generosity.
> A few examples:
- Foundations of tall building must go to bedrock - not true.
I see few if any comments here asserting, let alone asserting without qualification, that buildings must be built to bedrock. Further, heeding your own advice that expertise should be bidden, note that the apparently expert sources in the article said themselves that not building to bedrock can be a problem.
I see people here noting and reflecting that expert opinion. Few if anyone going beyond it. And you're not reading the source material carefully enough if you miss the take that not building to bedrock can carry some risk.
> - Large buildings settling is unusual - not true.
Again, I see no one or very few people here saying this. Of course buildings settle over time. And here in this thread, contrary to your blithe and dismissive assertion, we even have people pointing out that settling happens not just in towers but in buildings of most any kind.
Note as well, again, that the very experts you appeal to say that this tower's settling is both comparatively fast and that its magnitude is unexpected. These are the experts talking, so you come off as hypocritical at best here. The nature and particulars of the settling in this particular case appears noteworthy and to be a reasonable cause for concern.
> - Earthquake safety has been compromised in this case - not true.
Ahh... so, now you are the expert and capable of refuting this possibility so entirely-- upon merely a cursory examination of second- or third-hand information, rather than a primary analysis, no less-- that it is somehow faulty for people to question whether this might have an impact on earthquake safety? My, my; odd that you called for caution in drawing conclusions until experts had weighed in, then turned around and flatly conclude that which I doubt even experts would leave completely unqualified, and certainly not universally and unanimously so.
The comments here so far are not much of the chicken-little or even rabble-rousing type. Try being more respectful toward your fellow community members.
The 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?
I don't know what skyscrapers do but throughout SF one can find smaller houses that have subsided. They dealt with the problem by adjusting the sidewalk and adding ramps, some of which are absurdly steep now.
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 hard it could not be dug with hand tools.)
I did have a scare because a spring appeared on the edge of the property, as underground water is indicative of slide risk. Fortunately, it turned out to be a leak in the water main!
I still made sure the hard surfaces all drained into the storm drain, so that the hill wouldn't become saturated with water.
I can't conceive of building a 58 story building on sand in an earthquake zone. Reminds me of that Monty Python quote:
"When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built in all the same, just to show them. It sank into the swamp. So I built a second one. That sank into the swamp. So I built a third. That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Lad, the strongest castle in all of England."