Timber!
"... listing a few inches to the northwest, ..."
Gee, anybody wanna take bets as to where this will fall in the next earthquake?
San Francisco's $350m leaning Millennium Tower is continuing to sink into the ground, European satellites orbiting Earth have confirmed. The 58-story landmark, at 301 Mission Street, is one of the tallest structures in the tech-playground city, overlooking the bay and the metropolis's startup land. The swanky skyscraper, an …
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Actually you have a point there. If SF gets hit by a major quake, the ground under the tower might suffer liquefaction since it is only landfill and not bedrock. At that point the concrete slab that the tower is built on will sink. If they are lucky it will sink straight down, but the odds are that one part of the slab will tilt which means the whole tower will start to lean over. At that point being somewhere else would be a very advisable strategy.
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How about the next quake that hits the San Francisco Bay Area measuring between 6.8 and 7.2? The way I see it, anything over 7.2 is so unlikely that neither you nor I will likely be alive when (not if!) it hits, and anything 6.7 and under is barely worth getting out of bed for.
Before you answer, digest this:
http://pubs.usgs.gov/fs/2015/3009/pdf/fs2015-3009.pdf
WARNING! 6 page PDF totaling 32+ Megs! WARNING!
Such a clusterfark - the developers were too cheap to sink the piles all the way down, and now they're saying they don't even have to fix it, they can just let it sink and it'll stop eventually.
But there's no reason to believe that 31 inches is an actual limit - that was an estimate from an engineer hired by those same shady developers. It could sink another 100 feet - which would be fine, the big problem is if it falls over. Real China Kwalitee there guys.
At least for once the victims are also rich tossers.
> At least for once the victims are also rich tossers.
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That's not a helpful attitude. The same design process that put up this skyscraper is also behind the skyscraper you go to work in, the stadium you see your football in, the train station you wait for your ride home at, and more. You may laugh now because the "rich tossers" are getting screwed, but what happens when the skyscraper you're working in falls over during an earthquake and pancakes you? Are you going to have the same happiness about *that* engineering failure?
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> the developers were too cheap to sink the piles all the way down...
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Yes, cost is a consideration in almost all engineering projects. Was it necessary to sink the piles all the way down, given the results of the site survey and proposed design? The slide rulers said no at the time. Hindsight is 20/20.
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> and now they're saying they don't even have to fix it, they can just let it sink and it'll stop eventually.
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Buildings are usually over-engineered to provide for a safety margin. Bridges, for example, may be rated to hold 100 tons, but may in fact be designed to hold 200 tons, to account for unexpected load. Subsistence is also calculated ahead of time, and a safety margin is present there as well: All buildings will sink. They build it so that it can sink farther than expected and still be safe. In fact, the Japanese built an entire airport on a man-made island that is sinking at many centimeters per year... and all of the structures there are built on jacks. It's actually quite remarkable. So if something sinks more than expected, that doesn't mean the safety margin has been exceeded. Hence, nothing needs to be done, provided this new behavior is thoroughly understood. Is it? I don't know, but it's not necessarily a wrong answer.
> But there's no reason to believe that 31 inches is an actual limit - that was an estimate from an engineer hired by those same shady developers.
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All engineering disciplines use estimates, rules of thumb, and the like. There's every reason to believe that engineer: If he's wrong, his career might be over. As to "shady developers"... you know, when something goes wrong, it's usually not due to malice but incompetence or ignorance. You can't scream "Illuminati!" whenever anything goes wrong. Car didn't start this morning? IT'S A CONSPIRACY! Or, maybe it's just been 7 years since you last replaced the battery... something you might have overlooked.
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> It could sink another 100 feet - which would be fine, the big problem is if it falls over.
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Having a building descend 100 feet into the ground at the center of a major city when it was built to sit on top of the ground is never "fine". I've watched movies where that happens, and played video games. It rarely ends well for the people living in said city. Usually there are demons, fire, aliens, or other things that tend to drive down property values to go with it.
Yes, cost is a consideration in almost all engineering projects. Was it necessary to sink the piles all the way down, given the results of the site survey and proposed design? The slide rulers said no at the time. Hindsight is 20/20.
According to the San Francisco Magazine article, this type of building had been rejected before:
At around the same time Millennium Tower was moving toward approval and construction, developer Jack Myers submitted plans to erect a skyscraper at 80 Natoma, just two blocks away from the Millennium’s site. It would, like the Millennium, be a poured-concrete structure, though a daintier 52 stories instead of 58. As described by then–DBI director Frank Chiu in 2004, the proposed tower at 80 Natoma and the ground upon which it would have stood reads like a mirror image of the Millennium: It would be “thin relative to its height,” “built on soft soils that are subject to compression, and supported on short piles that wouldn’t reach the bedrock 190 feet below.” Also, it would be “an extraordinarily heavy structure.”Sans in-house rocket scientists, Chiu called in outside experts for detailed analysis on 80 Natoma. After a full peer review of the building, its foundation, and the soil, Chiu wrote that the experts had determined that “the building could settle an alarming and unacceptable 9–11 inches.”
The maths were already done on a similar building, in similar conditions, practically next door. It was rejected, and for good reason. Somebody important in the city planning office knew that the Millennium Tower would have severe problems after it was constructed.
Just because a building is "constructed to code" doesn't mean that the finished build will be safe. The building leans, and may have to be torn down.
> The maths were already done on a similar building, in similar conditions, practically next door.
Two blocks away marks the start of landfill. It was a swamp before. All you've done is pointed out why engineers do site surveys before they build: Because the geology even "right next door" can be radically different. It's a very good thing civil engineers don't have the accumen of internet pundits, or the first wood pecker to come along would destroy civilization...
But the Dutch know how to build on soft soil. The Royal Palace in Amsterdam was built as a town hall between 1648 and 1665 on 13659 wooden piles. It is still erect and in perfect condition standing on that same wooden piles (minus two, taken out for inspection) protected by groundwater.
Controlling groundwater levels is essential in the Netherlands, especially in the parts that are below sea level. For that they have elected councils with a tradition going back to the 13th Century.
But, and I think this is an important point, the Dutch do not have to worry about magnitude 7+ quakes hitting them. Just remember that SF is right where the San Andreas fault can clobber it - in fact that is exactly what happened to the city a little over a century ago. Also (before someone decides to mention it) the SA fault does not run through the city - it actually takes the scenic route through the bay. Major SA quake on the SA fault = tsunami right up the San Joaquin valley. Not fun!
Saying that, I remember hearing that LA was once described as "a city waiting to die".
This really made me smile and I absolutely don't want to make you feel like I'm saying this in a mean way because I genuinely love it, but there is a noticeable difference between a woodpecker and a wood pecker.
If you're talking about a bird, you probably mean the former...
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In fact, the Japanese built an entire airport on a man-made island that is sinking at many centimeters per year... and all of the structures there are built on jacks. It's actually quite remarkable. So if something sinks more than expected, that doesn't mean the safety margin has been exceeded.
Kansai Airport has sunk far more than expected, and there is some nervousness that it won't stop before it sinks beneath the waves. The building jacks keep them level, but won't keep them dry.
The loss of Kansai airport would be hugely problematic; they're planning on closing Itami airport in nearby Osaka, leaving just Kobe's small airport as backup. Basically the whole region needs Kansai airport to stop sinking.
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> Kansai Airport has sunk far more than expected, and there is some nervousness that it won't stop before it sinks beneath the waves. The building jacks keep them level, but won't keep them dry.
There isn't any nervousness. Yes, it's sinking more than expected, but there was a high degree of uncertainty in that project: Nobody has tried something like this before. They can remove the jacks and sub-flooring if needed and add bigger jacks. The airport has a sizable boundary around it so they can add more landfill in without disturbing the buildings. There are contingency options here because while the best estimates they had said it probably wouldn't be needed, there were a lot of unknowns in the model. I have no doubt the airport will still be there in 30 years. I don't know what will be needed to keep it there, but it's not like Godzilla is going to crawl out of the ocean and eat it.
Well, not since Atlantis, you can find the original engineer's report and planning permission buried in soft peat at the local planning office.OTOH if you're frightened of leopards Tall building foundations: design methods and applications from Innovative Infrastructure Solutions December 2016.
Not forgetting all the cleaners, security guards etc who'd be in the building and are definitely not rich by any Western standard...When The Git pointed out that they aren't "rich tossers" his post was downvoted, then deleted by the moderators. In <El Reg's</i> New World Order, they appear to be deemed "rich tossers". Not The Git's world...
"the developers were too cheap to sink the piles all the way down"
considering it's San Francisco, I offer these possible excuses:
a) endangered gophers/moles preventing a proper pile-drive
b) the term 'pile driver' was considered to be an epithet and summarily struck from the list o' instructions for proper building construction
c) too much dope smoked on the job
d) they wanted a NEW tourist attraction: the 'Leaning Tower of Frisco' [note S.F. area residents *HATE* it when you call it 'Frisco']
e) gummint corruption allowed improperly inspected construction
f) it was NOT built by Trump [I had to throw THAT one in there!]
If you dig into it you'll find out that the site survey and build was done to all engineering standards; The problem is that, after the preliminary design and survey work, and construction had started, the city decided to start building a new transit station nearby. This involves dewatering -- pumping water out of the foundation so that it can be compacted more easily, and there is less settling in the foundation. The problem is, the way they are dewatering is that it removes water from everywhere nearby, not just the area directly under where the new transit center will go. As a result, the sand under the Millenium Tower is compacting at a highly accelerated rate, and it is doing so unevenly.
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Now yes, there is finger pointing over who knew what, when, and all of that, but this is not a design flaw. This is not an engineering flaw -- when the designs were approved and the survey completed, everything was done by the book up until that point. What has happened here is a external and unanticipated factor.
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As to building foundations down to bedrock -- while yes, that could have been done, there was no need. Many, if not most, of San Francisco's buildings, do not have foundations that go all the way to bedrock. In fact, in an earthquake-prone area, this is often a *bad* idea because during a quake, all of the wave action will be translated via those concrete pillars directly to the building. You have to build in extra dampeners, possibly a counter-weight / pendulum system, to absorb all of that extra mechanical force -- which isn't necessary if the foundation doesn't get nailed into the bedrock... Instead, the sand, gravel, etc., absorbs that stress and there is less mechanical force being forced into the building structure.
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So I need to be absolutely clear here: The building's design, including foundation, and the surveying done ahead of time to ensure it would be sufficient, was done to textbook. There were no flaws. The flaw here, is that something was built right next to it right after it went up -- before it had a chance to settle naturally and compact the foundation evenly. All buildings settle, even skyscrapers. There are models to predict how much and how long it will take (Typically, it takes about 20 years before it becomes insignificant).
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Now, all that said, this is a classic case of tragedy of the commons: If your property has a drainage ditch that prevents flooding for your neighbors' properties, and that drainage ditch becomes obstructed somehow, are YOU responsible for fixing it, or are the people benefiting from it (ie, your neighbors)? This is a very simplistic example, but it's fundamentally what this entire affair boils down to: Transbay dewatered the area for its own project, and in doing so, led to the problem the Millenium Tower is facing. Who knew what, when? We probably won't know for a long time. But ultimately, this is a question of who is going to pay for the foundation to be reworked. This could cost $10 million dollars, or much much more -- it varies by site and building, but a similar problem has happened in Brazil, known as the Leaning Towers of Santos, and it's over a hundred buildings all suffering from the same problem. That's about the cost for these smaller apartment blocks, per building... and so far, nobody has stepped up to pay for it; Though, when they were built, subsistence was not as well-understood as it is today.
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"So I need to be absolutely clear here: The building's design, including foundation, and the surveying done ahead of time to ensure it would be sufficient, was done to textbook. There were no flaws. The flaw here, is that something was built right next to it right after it went up -- before it had a chance to settle naturally and compact the foundation evenly. All buildings settle, even skyscrapers. There are models to predict how much and how long it will take (Typically, it takes about 20 years before it becomes insignificant)."
Based on what?
1) If you read the articles it clearly states that there was no comprehensive design review done because the developers refused to do one and the planning department didn't think they could for the to.
2) This building is uniquely heavy given its small footprint and the decision to use concrete instead of steel (equivalent to a 150 story steel building).
3) It had sunk almost 12" before Transbay started construction, 50% more than the lifetime projected amount the developer's engineers had predicted.
4) It's tilting AWAY from the Transbay construction, the developer is attempting to argue that the de-watering is causing it to tilt in the opposite direction WTF?
- "here is a leaning high rise, very noticeably so, in Vancouver BC. I believe they solved the problem by freezing the underground."
- "I suspect that particular solution is a lot easier to achieve in Vancouver than San Francisco."
Not at all, as long there is some water in the ground that you can freeze. The technology is availiable, tried and tested. The energy bill for keeping the refrigeration units running 24/7/365 for as long as you want to keep using the building, however...
If you read the articles it clearly states that there was no comprehensive design review done because the developers refused to do one and the planning department didn't think they could for the to.I somehow don't think San Francisco is in the 3rd World. Developers hire accredited engineers to design buildings to comply with the Building Code. The City employs or hires Building Surveyors who certify that the design either complies with the Code, or is "Deemed to Satisfy" the aims of the Code. Only then is a Building Permit issued and building commences. During construction, Building Surveyors (often called Inspectors at this stage) visit the site to ensure that the building is being erected as per the design and including any special instructions issued with the Building Permit.
Blaming the developers is a big stretch unless they suborned the Engineers and/or Building Surveyors. If the latter, then they are culpable since this is professional misconduct.
> Blaming the developers is a big stretch unless they suborned the Engineers and/or Building Surveyors. If the latter, then they are culpable since this is professional misconduct.
First, I agree with everything else you've said. But this isn't and either/or conclusion -- the amount of oversight by the government varies considerably from one municipality to the next, and most of these agencies are criminally underfunded. These agencies provide almost no additional safety. Example follows.
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One of the worst building engineering disasters was the collapse of a pair of walkways inside a multi-story hotel: Until 9/11 it was the worst structural collapse in US history. The hotel had about 800 rooms and was maybe 20 stories tall -- The building inspection for the site took less than 15 minutes. It was eventually determined that the engineers were responsible, that this was a bona fide design flaw, but despite dozens of people being involved in the project, numerous government agencies, and other safeguards, a very obvious structural flaw was overlooked.
My point here is that the majority of the safety of buildings comes from good engineering practices within the companies doing the work. There is no real oversight or auditing beyond that, so unless there was a very obvious flaw it is unlikely inspectors would discover it. Corruption might be a problem if there was any real risk of a project being stalled out by such a problem getting discovered... but the odds of it happening, realistically, are about nil. The inspectors are overworked to the point of being ineffectual.
There is no real oversight or auditing beyond that, so unless there was a very obvious flaw it is unlikely inspectors would discover it... The inspectors are overworked to the point of being ineffectual.Third World it is then. I am surprised, especially since Merkins are less than hesitant to describe Tasmania as "Third World". The last five years of my working life (to my everlasting shame) I worked in the civil service (Building Compliance).
Source please? I smell bullshit from the building's developers being swallowed whole by a gullible Reg commentard.
It is well known that loose material such as soil, sand and gravel becomes HIGHLY unstable during an earthquake due to a process known as liquefaction. That could mean the difference between the building getting a big shaking and swaying (as tall buildings are designed to do) during a quake, and a building suddenly dropping dozens of feet as it and its piers act as if all that sand and gravel has been magically transformed into water. Even if it remains standing I think you can guess the result would be far worse than getting "wave action translated by concrete pillars" embedded in bedrock.
a structural design change was made for aesthetics. So in that case yes you cane blame the engineers for no recalculation load strength.Aesthetics is the province of the knarchitects*, not the engineers. If the knarchitects never passed the revised drawings to the structural engineers, why would you blame the engineers for failing to anticipate those changes? Makes more sense to blame the Building Surveyors who accepted the design change without revised engineers' drawings.
* knarchitect is an engineer's term for them that make pretty pictures.
There seems to be a lot of ignorance here about the effects of different terrains on earthquake damage. The fact is that a thick layer of soil (or landfill) between bedrock and the buildings does not "cushion" the waves, it amplifies them.
Generally structures sitting directly on bedrock do much better than those on fill or soil. Damp soil is the worst because of liquefaction, something less likely in this case due to that dewatering thing.
I only know about this stuff because of where I was raised: Southern California. Whole lotta shakin' goin' on there...
> There seems to be a lot of ignorance here about the effects of different terrains on earthquake damage. The fact is that a thick layer of soil (or landfill) between bedrock and the buildings does not "cushion" the waves, it amplifies them.
This is why I generally shake my head and mutter whenever someone from Southern California tries to sound edumucated. The other 47 states on the continent keep praying you guys fall into the ocean so as to rid us of your stupidity, but the geologists keep telling us it's going to take too long. Sigh. So here we go again, from the top:
*** There is no bedrock in the San Francisco bay area. ***
************** 404: GEOLOGY NOT FOUND. **************
Bedrock sounds like a really nice, reassuring word, and of course everyone wants to know why every building doesn't simply drill down to bedrock. Well, there's a simple engineering answer: It's not necessary. Foundations in a building serve only one purpose: Load spreading. And the method used for constructing the tower is a proven one: Friction piles. To understand how they work, take the wooden handle of a broom and push it into the ground. Hammer it in, if you want. You're not going to get very far down, and that's just dealing with the topsoil and clay in your backyard. Friction piles operate on the same principle: They're just a lot bigger. They will easily support the weight of many, many tons without moving, because the static friction along the sides keeps it from sinking. That's how the Millenium Tower was built, and it's solid engineering practice. And there is zero risk of liquifaction here: The foundation is irrelevant, the geology of the site isn't suseptible to it unless you have an earthquake of a magnitude that would wipe out pretty much everything except a military bunker.
I have said it before, and I will say it again: The design is solid, and the site survey was done properly and to best practices. What was *NOT* done correctly was the dewatering of the whole area, which radically changed the friction and compressibility of the soil under the tower, and that's what has caused it to sink and tilt. There is no disagreement about this amongst engineers. You can't expect the engineers to have anticipated that, after construction, the next door neighbors would fuck up the geology under the building like this: Their dewatering has dropped the water table by over 20 feet. The piles that previously were in the water table are now sitting above it. Water tables do not simply drop by 20 feet in a coastal area in the span of a few months. It's not a natural process.
So please, stop acting like you know something about engineering: You don't. And as far as the waves being amplified: Learn the difference between primary and secondary waves, because one induces compressive load and the other shear load. If you build down to bedrock, your piles need to be able to withstand both as first-order effects. If you don't, the piles only need to worry about compressive load because there won't really be any sheering... the building will move with the earth underneath it (which it wouldn't, if it were nailed to the bedrock). Though in practice, all of this simply means tweaking your concrete mixture... the design will be the same.
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> "There is no bedrock in the San Francisco bay area."
Say, since you're so "over-edumucated," would you like to buy a nice bridge in Frisco? Guaranteed to be free of that pesky bedrock!
Seriously MNGrrrl, who told you there is no bedrock under SF? There is, you know. Might be too deep to build on but it's there. It's everywhere if you go down far enough, and the earthquakes don't care if the sediments are really thick (by our tiny standards). Also I never mentioned anything about engineering, but you pretended I did so you could attempt to denigrate my intelligence. Do you feel really smart when you do that? I bet you do.
> Seriously MNGrrrl, who told you there is no bedrock under SF?
There is no bedrock at or near the surface. Source: US Geological Survey department. https://earthquake.usgs.gov/regional/nca/soiltype/ "Includes unweathered intrusive igneous rock. Occurs infrequently in the bay area."
Anyway, nice strawman you made there. You should put a hat on it though and some sunglasses and really complete the look.
@MNGrrrl sez:
"Anyway, nice strawman you made there."
Okay, you got me. I DID realize you really meant that the SF bedrock was inaccessible and not absent, true enough. But after your unprovoked personal insult against me I felt it was legit to rub your shiny little nose in that categorically absolute (and laughably incorrect) statement of yours.
You got a problem with that, or only with people from SoCal, fule?
In future, when trying to tear down others to get your jollies you really ought not spout inanities. It leaves you wide open. I can't be blamed for walking thru a door you conveniently blew off the hinges, can I?
I believe many of the cathedrals from the middle ages are atop wooden piles.I'd like a reference for that. Most of the excavated cathedral foundations I've read about are rubble and quite massive. The foundations of Notre Dame are more than 10 metres deep and at Reims more than 12 metres wide and are definitely stone, not timber.They were also using wooden piles for large buildings in 19th century St Louis.
Guess it's all steel now though.
Modern foundations are usually concrete. Concrete piles don't contain reinforcing steel as the stresses are compressive, not shear.
Venice is sinking too.... and each building is not as heavy as this one. All of the area of the Po delta is subject to subsidence too, especially as long as the river mouth moves forward, and the sediments dry and slowly compacts. The last Roman capital, Ravenna, saw its territory greatly changed through the centuries - it was one of the main Roman harbours - now it's no longer a seaside town. Some of its largest ancient buildings are now sunk two metres into the ground.
"Most of the excavated cathedral foundations I've read about are rubble and quite massive."
I was specifically thinking about Ely Cathedral - but looking it up, the foundations are as you describe.
Interesting - it had a tower collapse because of uneven subsidence.
"Most of the excavated cathedral foundations I've read about are rubble and quite massive."
The columns of the central crossing of York Minster was built above Roman remains. The original builders hadn't gone down deep enough to remove them. Differential settling resulted in the spire repeatedly collapsing followed by imminent collapse of the whole structure. It was eventually excavate and the columns underpinned with proper concrete foundations (reinforced). It's worth a visit for anyone passing through York.
Beverley Minster's north transept is also well askew but not as bad as it was before a C18th repair. http://www.yorkpress.co.uk/features/features/11421579.Beverley_Minster___a_parish_church__not_a_cathedral___/?ref=mmsp
Maybe what SF needs is a Nicolas Hawksmoor.
The columns of the central crossing of York Minster was built above Roman remains. The original builders hadn't gone down deep enough to remove them.It's quite common to find churches and cathedrals being built on the foundations of a prior building; usually a church rather than a Roman building.
I seem to recall Basil Spence being castigated for his replacement for Coventry Cathedral which isn't built on the remains of either St Mary's or St Michael's. Fond memories of seeing the new cathedral shortly after it was completed (1962?) and sniggering at the sight of Satan's exposed dick. Doubt I will ever see York Minster as I find travel more than tedious these days. Sad really as I do enjoy looking at old buildings...
Oldest ones are often built on Roman buildings (if they didn't reused the whole building changing it into a church), because of lack of previous churches... there was the need to replace temples with churches to establish the new religion - and even Christians had (and still have) that strange idea of "sacred places" - which is as old as mankind, probably, and very little Christian.
Moreover, before mechanical excavators, even with a lot of slaves or serfs, it wasn't easy nor useful to clear a whole area from previous building. If the building wasn't re-used it was demolished, part of the material re-used, other used to fill the and level for the new building. Actual cities in Europe may be several metres above the old ones.
Sounds painful.Wouldn't really know as I never suffered from them. But I thought they were itchy rather than painful. Perhaps we should be inspecting the builders' purchase orders for large quantities of AnuSol. This apparently shrinks piles through "scientifically proven" 3-way action! Speculating whether the "scientific proof" was supplied by Stephen Fry ;-)
Winchester Cathedral was built in the 11th century and in the early 20th century was in danger of collapse because it was built on a raft of beech-tree trunks which floated on layers of clay, peat, and mud. It was saved from collapse by the actions of a diver who propped up the foundations with bags of cement, a process that took over six years.
https://www.flickr.com/photos/brizzlebornandbred/27727635574
"Guess it's all steel now though."
I would have guessed reinforced concrete, actually, driven in by diesel pile drivers. it's a pretty cool design, actually, a one-cylinder diesel engine in effect, where the weight goes up when it goes 'bang', then comes back down to ignite fuel/air and keep it running. I've seen them going off nearby when I was in the Navy, when they were building an extension to one of the piers. They don't start running properly until there's enough friction to bounce the weight up sufficiently to get that nice steady bang, bang, bang...
Lots and lots of (very) old buildings rest on wooden piles, usually oak. But they usually are not friction piles. Basically, you take lots of ex-trees and hammer them into the ground quite close to each other, thus compacting the earth/mud/whatever between them. The piles and compacted earth form one big slab that is big enough to spread out the load from the building sufficiently.
Friction plays some part, admittedly, and sometimes the piles are long enough to reach rock or whatever, but these are side effects.
In order for friction piles to work properly, you must actually spread them somewhat so that every pile has it's own chunk of earth to cling to, so to speak. The rest is about the pile's lenght and diameter, i.e. the resulting surface area. The survey of the site will give data about the amount of friction that can be transferred from the pile into the ground per unit of surface area. That will give you the dimensions the pile must have (plus a generous safety margin).
Wooden piles last very long if they are always completely submerged in groundwater (or are always completely dry). If the pile is sometimes submerged and sometimes not, due to fluctuating water levels, it will rot. Usually that's the top of the pile.
Which means that a buliding that has stood for ages can get in trouble if someone next door starts dewatering for the big excavation he's planning... which means it's time for diaphragm walls... but that's another story.
Time line:
2009, construction completed. Expected subsidence: 4 to 6 inches.
2009, DBI deputy director Raymond Lui writes letter raising questions about building's sinking.
2013, TJPA began dewatering. Millennium Tower had already sunk 12.1 inches, two to three times what was expected for its entire lifetime.
2016, Millennium Tower has currently sunk 16 inches.
While the dewatering of the TJPA project and 350 Mission Street project and other nearby projects may have contributed to an additional four inches of subsidence, it remains that by the time the first project started, the building had sunk just over a foot down.
On the bright side, the building will still have the vast majority of its height above ground, even if it sinks down to the bedrock. ;)
Bedrock, to quote the USGS, is "the hard rocks that make up the hills and the ancient and active earthquake faults", and as you can see from their page on SF Bay Area geology, there's no lack of it here:
http://geomaps.wr.usgs.gov/sfbay/geolist.html
""I somehow don't think San Francisco is in the 3rd World.""
"Yet. The city council is working very hard on getting there..."
You mean the City Council is planning on making San Francisco a sovereign state aligned with neither the USSR or the Western/NATO alliance?
The whole "First/Second/Third World" idea was Cold War propaganda where the "First World" were nations aligned with NATO/Western Nations; Second World nations were aligned with the USSR and third world nations were those that remained neutral towards both groups.
Technically Switzerland was a third world nation while Liberia was considered First world. Its all random bullshit to make us seem like civilized and superior to those not towing the party line.
Your definitions were true fifty years ago, but today common usage includes GDP, GNP, literacy rates and the Human Development Index in determining ranking. From Investopedia:
First-world countries have stable currencies and robust financial markets, making them attractive to investors from all over the world.[Second world is] A country that is more stable and more developed than a third world country but less stable and less well-developed than a first world country.
Third World countries are for the most part poor and underdeveloped. In these countries low levels of education, poor infrastructure, improper sanitation and poor access to health care mean living conditions are inferior.
"Third World countries are for the most part poor and underdeveloped. In these countries low levels of education, poor infrastructure, improper sanitation and poor access to health care mean living conditions are inferior."
Does poor include the definition of "indebted for 18 years or more of GDP?"
*cough*
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, too. 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!
The city council is working very hard on getting there...It's a race to the bottom... Our local council was sacked recently by the relevant state Minister. The only surprise was how long it took for him to make the decision. It wasn't corruption; merely rank incompetence. So it goes...
I somehow don't think San Francisco is in the 3rd World
You would be surprised at some the 3rd world actions committed in the U.S.
American developers are notorious thieves and liars and cheats. Local government agencies are "influenced" every day. The corruption is as bad as every empire in history ever was.
> Based on what?
Based on the plans filed with city hall, and independent review by other engineers. Do you seriously believe something like this is an everyday occurance in the field? A building falling down, or even having the potential to fall down, is a big deal. If there was a design flaw, or the survey was done badly, we'd know it by now. There would be klaxxon alarms going off, engineers would be going to their local media and saying "There be dragons here". It would be a Very Big Deal.
1) If you read the articles
... written by non-engineers with only a tenuous grasp of the subject material. Also, said articles as linked to by El Reg failed to note the dewatering at a new construction happening right next to the building. That's, uhh, kindof important.
2) This building is uniquely heavy
... Compared to what, exactly? Is this the first skyscraper ever built? Does every floor have giant lead plates bolted to it? Have buildings never been made out of concrete before?
3) It had sunk almost 12" before Transbay started construction, 50% more than the lifetime projected amount the developer's engineers had predicted.
The estimates for the subsistence were based on how much it would sink *after* completion. Again, this is what happens when you ask journalists (and apparently random internet pundits) to review technical and engineering studies and data, without knowledge of the field.
4) It's tilting AWAY from the Transbay construction, the developer is attempting to argue that the de-watering is causing it to tilt in the opposite direction WTF?
The ground directly under your feet may have a very different composition than what's 20 feet away. Just because it looks the same on the surface, does not mean it is the same underneath. Dewatering, if containment is not done (or done improperly) can affect the ground for miles in every direction. Fracking, something that has made the news recently, has been responsible for earthquakes that have affected buildings hundreds of miles from the site of the injection. This is why it is so important to conduct a proper site survey prior to construction: The Millenium Tower developers *did* do this. The Transbay developers *did not*. If they had, they would have realized the need for containment, and it's just plain reckless to dewater a site right next to a recently constructed multi-story building. Any civil engineering student would tell you to be very, very, careful when doing multiple constructions projects near to each other without coordination.
"If your property has a drainage ditch that prevents flooding for your neighbors' properties, and that drainage ditch becomes obstructed somehow, are YOU responsible for fixing it, or are the people benefiting from it (ie, your neighbors)?"
That particular question was answered centuries ago as far as England was concerned. Manorial court roles are full of pains that everyone should scour their ditches (and mend hedges or whatever part of the common infrastructure needed maintenance) and individuals being amerced for failing to do so.
>>estimates, rules of thumb (and rather than)"shady developers" it's usually incompetence or ignorance.
I'll be looking forward to learning the full story at some future date. In the short term I expect A LOT of energy spent covering backsides and plenty of finger pointing. I'll be betting that "normal" practices were followed for the most part and that somehow ignorance is involved.
Don't worry. The next President has an extensive knowledge of the matter. It will launch his campaign "make America tall again" which will allow for building new storeys to keep the skyscraper tall enough while it sinks. While a new law will ban suing developers for such mundane matters. Of course it's just ambientalists' fault - if you pour enough concrete everywhere Earth will be much, much more resistant. And while pumping water out is a no-no, pumping everything else is OK, you can always use potable water to fill the gaps later.
Seems that every time I am in San Francisco, they discover the remains of a wooden ship or two while excavating a construction site.
Compare a map of the God Rush era San Francisco to the city's shoreline today, and you find that a lot of what is land now was water then.
Same in New York City - witness the ship under the WTC. But I believe they don't have a problem with reaching bedrock.
> Same in New York City - witness the ship under the WTC. But I believe they don't have a problem with reaching bedrock.
NYC is an interesting and useful comparison. I recently learned that, looking at a map of Manhattan, all of the high rise buildings are in two fairly small areas of the island. Buildings on the rest of the island are limited to five or 10 stories. This is because only those two areas have solid bedrock. The city does not allow super high rises on those other areas, with or without piles.
These tall skinny buildings are a special problem. A cathedral is tall, but not that tall in proportion to its footprint - the height is maybe three or four times the width. So building on a lesser foundation may cause settling, cracking, etc. but is unlikely to result in the entire structure tipping over. But a 60 story building (maybe 700 feet tall) on a 60 or 70 foot wide lot has a lot of leverage, so a tiny bit of tilt will quickly start to escalate as the weight gets concentrated on one side.
I think they're planning on screwing a huge eyebolt into it about halfway up and using the local fleet of tugboats to yank the building perpendicular. Personally I think they ought to let the public join in. Y'know, college sculling teams, swimmers, jet skiers, garbage scows. It would be a real party!
I can just see the come-on: "Peepuls! Drag yer azzes down to the waterfront on Saturday and help make San Francisco straight again! If we all pull together we'll really pull together!"
Two details to reinforce what was said before:
This building is notably heavier (has higher ground pressure) than others in the city. Rather than being built primarily of steel with a relatively thin concrete covering, as is common with commercial buildings, this building is primarily built of concrete.
Using primarily concrete is weaker, heavier, and harder to modify. On the plus side is quieter, much less expensive to build, and more robust in a fire. For residential construction it's easy to market the advantages as making this a superior approach.
The developer is blaming the city and its recent near-by construction. Why? Solely because the city has deep pockets. The tower was sinking rapidly before that construction started, and is tilting away from the excavation. If anything the construction is temporarily reducing the tilt, although it's most likely that it's having a negligible influence.
But what no one is saying is that it's unreasonable to use a foundation so inadequate that no adjacent construction can ever be done. This is in the middle of a city. In the expected lifetime of a building it's probable that every adjacent lot will have the existing buildings torn down and new larger ones constructed.
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Given that the building had slumped a foot before any dewatering took place, which was more than the lifetime expectation, I feel this 'sue adjoining properties' scheme is going to be a tough one to argue.
However if the tilt is more recent, then that could be attributed perhaps.
I'm sure a solution will be found, but clearly in hindsight building a massive concrete stiletto on deep soils might not have been the best plan up front.
clearly in hindsight building a massive concrete stiletto on deep soils might not have been the best plan up front.Yes, a skyhook would have worked much better!
I think you will find that the reason for building from concrete rather than steel and curtain walls is the Great God "energy-efficiency" because of thermal mass.
Apparently they can detect if I'm slouching on my way to the supermarket today? I think that is a blatant invasion of my privacy tbh.
And why do we even carry tape measures anymore? I'd like an app that tells me the dimension of everything I point at with 1mm precision, measured by same sattelites.
In a city that is known for its earthquake hazard, and that is built on landfill, failing to require the piles for this building to extend all the way to bedrock is an engineering failure on the part of the city's building department as well as the developer. Landfill, especially near a large body of water that can provide lubrication, has a tendency to liquify under earthquake stress. There are videos online of the dirt flowing up through sidewalk cracks during earthquakes.
Both the developers and the city are in deep doo doo. And should be.
Both the developers and the city are in deep doo doo. And should be.The city I can understand, but why the developers? Because they engaged Handel Architects, DeSimone Consulting Engineers and Webcor Builders? Perhaps they should have engaged Gary Bickford, but I have no idea why.
Since several commentards appear to know little about the building process:
First up is the Developer. In the case of very large buildings, such as the one under discussion, this is usually a very wealthy corporation such as an insurance company, or bank. In the case of a home this can be the homeowner. The Developer hires:
The Architect in consultation with his/her client designs a suitable structure to satisfy client needs. This can include not just pretty watercoloured drawings, but also models that used to be made from cardboard, or balsa wood, but more usually these days is a "VR experience" on a computer screen.
When the Developer is satisfied with the Architect's design, the design drawings are passed to an Engineer who has to determine how the building can be constructed in such a manner it doesn't fall over, or blow away. Not always an easy task given the feeble grip on reality that some knarchitects possess.
If the design isn't described in the Building Code, then a Building Surveyor needs to be engaged to come up with what's called an Alternate Solution. That is, the design must be shown to meet the goals of the Code.
The proposed construction drawings are then passed to a Building Surveyor whose job it is to approve the structure and allow its construction. The Building Surveyor may be an employee of the Permit Authority (Council, City Hall...) or engaged on their behalf. The Building Surveyor will notify the Architect of any necessary design changes to meet Council requirements and these are not necessarily anything to do with the Code. E.g. Tasmania's Hobart City Council ordered the removal of red canvas awnings from a renovated bank "because the made it look like a Parisian brothel". Sadly, the resemblance was purely superficial and there were no exciting young ladies to be found therein.
The design is then passed on to a Quantity Surveyor who works out the cost of materials, labour and so forth that must be paid to complete the building. Usually this is twice the budget the Architect was required to work to though my own home would have cost 200% more if I had allowed someone other than myself to build it. I am assured this cost overrun has nothing whatsoever to do with Architects' fees being a percentage of the final building cost.
The building phase can now commence and is co-ordinated by a Construction Manager who may be the Architect, an Engineer, a specialist CM or even the building owner. The CM is responsible for hiring and firing the various tradies that undertake the physical labour component, as well as ordering the required materials in a timely manner. Another Golden Rule here; windows are almost invariably late in arriving, sometimes many months late.
During construction, the Building Surveyor (or a minion of) inspects the progress at several critical (Mandatory Notification) stages. The foundations cannot be poured in Australia until the Building Surveyor has inspected the holes and any required steel reinforcing for example. The final inspection on completion of the building results in an Occupancy or Completion Certificate.
FWIW, a good friend of The Git (a Merkin by birth) spent 30 years progressing from Permit to Build to Completion Certificate on his owner-built home. Something of a record I believe :-)
Depends a lot on the actual soil layers composition, and water presence.
"Recently" sedimented areas look to be prone to liquefaction. In the Northern Italy 2012 earthquake, that hit the eastern Po Plain, soil liquefaction was an issue and contributed to the collapse of many buildings (National Institute for Geophysics and Volcanology article, in Italian, and photos here: https://ingvterremoti.wordpress.com/2014/06/06/i-terremoti-dellemilia-2012-leffetto-della-liquefazione-e-le-conoscenze-sismiche-pregresse/ and https://ingvterremoti.wordpress.com/2012/05/30/terremoto-in-pianura-padana-emiliana-fenomeni-di-liquefazione/).
If you look at the photos, there are building in Turkey and Japan that fell on one side because of it. Think what could happen to a tall, heavy building....
That area of the Po Plain is a relatively "young" sedimentary one, and with a lot of underground water. Actually, removing underground water could help to reduce the risk of "soil liquefaction", because it's the increased water pressure during the earthquake that greatly reduces the soil grain friction turning everything into a "liquid". Thereby maybe the building sank more because of the soil compacting, yet there could be less risk of liquefaction. Then if the soil dampens or amplifies earthquake waves, and if it can still sustain the building, depends on the other factors.
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"The Architect in consultation with his/her client designs a suitable structure to satisfy client needs. This can include not just pretty watercoloured drawings, but also models that used to be made from cardboard, or balsa wood, ..."
These models are then shown to the clients.
(Actually, not that far from the truth, in my experience. Which makes it a timeless classic to me.)
"Tasmania's Hobart City Council ordered the removal of red canvas awnings from a renovated bank "because the made it look like a Parisian brothel". Sadly, the resemblance was purely superficial and there were no exciting young ladies to be found therein."
Given the many and creative ways banks can screw you in, I'd say the initial design was probably spot on.
Building on “the great layer of jelly in Chicago’s cake”"The soil was so slick that in 1856, Chicago lifted itself up to 14 feet off the ground to keep from sinking and sliding around in the mosquito-infested marshland." Good read for the layman laylady...
Thanks for the link, interesting read!
BTW, in the days before the great fire and the re-building, Chicago was basically a lot of wooden houses on stilts above a swamp. And this is actually where the term "underworld" comes from - the space between the raised houses and sidewalks and the mud. An ideal place for illegal activities or disposing of this and that. Like drugging, robbing and disappearing guests in a tavern - a landlord who used to do that a lot was one Mickey Finn.
One of the first things they do is hire a geotechnical firm like Kleinfelder or Signet Labs to drill and take core samples from the property and analyze the test results to decide what type of foundation would be the best for the area and the proposed structure. Usually all of the engineering firms agree on the recommendations before proceeding on the design and construction. If they decide to use a deep pile foundation they order usually 15 to 20 test piles that are longer than they need and drive them near where they took the core samples. They drive them to the point of refusal. The geotech engineer has computer leads connected to the top of the piles and as they are driven and analyzes the sound waves going thru them and how they are reacting to the soil. The average pile driving hammer weighs around 9000# and they adjust the fuel flow so it has a stroke of 4 to 11' depending on how hard the want to drive it. When they get to a depth where it takes around 35 blows to go 1' is where they would consider refusal. Any more force will tend to damage a concrete pile. Then a recommendation is made as to the number and length of the piles required to support the building.
A few blocks north of this site the 330' office building built in 2001 at 150 California St required
145-14" square concrete piles 102' long. The JP Morgan Chase building a few blocks west at 560 Mission St is 420' high and required 596-14" square concrete piles varying from 25 to 36' long. Must be some hard ground up the hill there. The dewatering process can cause problems. When the ground was dewatered in Sacramento for the new federal courthouse the parking garages around it settled and the walls cracked. A large PG&E utility vault settled and sheared off the main electrical cable supplying downtown Sacramento. What a traffic jam!
There had to be multiple screw ups on the Millennium project. I would bet on everyone involved suing everyone else before it is over.