Potential Fix to Right the Sinking 58-Story Millennium Tower IdentifiedJuly 19, 2017
A potential solution to right the sinking Millennium Tower, which has now settled a total of 17 inches with lean of nearly 14 inches as measured from its roof, has been identified.
According to the Chronicle, the conceptual plan includes “drilling 50 to 100 new piles down to bedrock from the building’s basement” and would cost an estimated $100 million to $150 million to complete.
Whether or not the tower would be able to remain occupied during the fix has yet to be resolved.
And of course, exactly who is going to be on the hook for covering the cost of any fix and damages could take nearly a decade to resolve, with the Transbay Joint Powers Authority (TJPA) now named in nearly a dozen lawsuits related to the sinking Tower at 301 Mission Street which is adjacent to San Francisco’s new Transbay/Salesforce Transit Center.
Comments from Plugged-In Readers
How do you hammer piles in a basement?
[Editor’s Note: You don’t. As quoted above, you drill (and fill).]
even so, drilling would certainly require a multi-story rig and that would presumably require demolishing parts of the garage to get the equipment in there and operating.
I’m guessing that they’re going to build a custom shorty drill rig to minimize the amount of disruption in the garage. The reason that off-the-shelf drill rigs are so tall is that they are intended to be used outdoors where there’s no vertical clearance constraint. The taller the rig the fewer times you need to stop and attach a new drill or casing segment. A short rig will also work but progress will be slower due to the increased number of times they need to stop boring and insert a new segment. And when they back the auger out the whole process goes again in reverse.
“drilling 50 to 100 new piles down to bedrock from the building’s basement”
Sounds like something they should’ve done in the first place.
Correct. The developer was penny wise and pound foolish. Or, he should give his architect firm a half Yelp star….
The architect has NOTHING to do with it.
The structural engineering firm is responsible for this problem.
Hmm. Maybe the architect should have had more to do with it. Their name is on the building and they chose to team up with a structural engineer that couldn’t deliver….The architects reputation is tarnished too. If the architect’s response is to say “not my problem” in this sort of situation – I certainly wouldn’t want to hire them.
Hmm, wasn’t the design of the MT also suspect for not going to bedrock in the first place yet they decided to go with a heavier concrete design? I have said it before and I will say it again, a lousy unlicensed handman contractor probably would have gotten this project right. I blame everyone, from the developer for being cheap to the architect firm, to the geologists, to the structural engineering firm, etc!!! This should have never, ever gotten to this point if people had a quarter of a brain….
So by that ill informed logic, the painter of the units should also be responsible. So should the tile setter, the carpet layer, the cabinet installer and the interiors stager.
No, you are being ridiculous. This whole project was doomed from the get-go. Does it take a genius, or a kindergartener, to understand that we are in earthquake country and on landfill and if you are going to build a heavier than usual building of this stature that maybe, just maybe you might, no should go to bedrock?
actually foundations are specified by the geotech engineering firm
As an architect myself with almost 40 years of practice, I have to say that a decision by the consulting engineer to NOT use drilled piers to bedrock for this project in ANY location, much less a fill area in a major seismic zone, would have raised HUGE red flags. Enough so to pay for a second opinion, and maybe enough to make me withdraw from the project.
Actually there was an article noting that about half towers in that area do not go down to bedrock. Those towers are also not as heavy and have higher percentage of steel vs cement. There was a comment that MT is about 6x as heavy per floor as a typical highrise in that area. I’ll need to find that reference again.
As an architect also, I would completely agree with you. And further, I have withdrawn from some projects I was hired for (residential architecture) during the initial design phases, mostly because of insane client demands that were either bordering on unethical and non code compliant, or just plain stupid design requests. My contracts always gave me the right to exit the contract with or without cause.
That’s pretty funny!
Folks, this is not gonna be the last time we read about this type of problem. The city’s plan to dump 400′ monsters at the “Hub” will result in the same problems, particularly the Goodwill site which sits on an old alluvial fan with high water table. The developer at that site is proposing the exact same foundation system the leaning tower used.
They did, but the piles didn’t extend to bedrock. “Friction piles” were chosen over “end-bearing piles.”
Why architects always have to come up with multiple solutions for a single issue when SE just needs to come up with one? The equipment for drilling probably takes 3 floors of garage space, if not more. Besides structural solution (i.e., add piles), I wonder if they ever thought about geotech solution, i.e. ground improvement such as jet grouting. They might be able to do part of it from sidewalk, probably less invasive to the garage.
Right – I’ve wondered if they can’t do what they did to the Leaning Tower of Pisa – extract mud/fill from under the higher side, to cause it to settle evenly.
Or could they cut the existing piles one at a time, installing jacks, and then once all are done, jack up the lower side and then brace the resulting structure in place.
how would this remedy prevent it from continuing to sink (and tilt) again afterwards.
Because you (re-)calculate the ultimate settling, and take out enough to compensate. Exactly at was done at Pisa; that tower was slightly re-straightened, and is now generally stabilized.
I thought there were no existing piles, which is (part of) what caused the problem.
The Tower’s foundation is currently supported by roughly 900 piles. But like most of the nearby towers, both existing and proposed, the piles were not driven down to the bedrock below.
The Pisa remediation was on a much smaller structure. And it required running tensioned bracing cables to nearby buildings.
I agree that there ought to be multiple solutions considered. Maybe they already have done this and are going with the best solution out of the mix. What is proposed: boring and filling, seems pragmatic. If they can cast new reinforced concrete columns all the way to the bedrock, it should halt the sinking.
I’d guess that they start on the lowest edge of the building to halt the worst of the sinking and allow the higher edge to continue sinking to level out the structure. Then finish the job along the higher edge.
could be difficult to ‘let it lean back’ because if it is leaning already, the center of mass of the building would already be pushing the building more in that direction. They might be able to help it by perhaps redistributing weight (i.e., vacating all the units on the lower side, adding ballast to units on the higher side).
The center of mass has only shifted a few inches so far. The vertical force is almost identical on both the high and low sides of the building. Once the posts on the low side have made contact to bedrock, the low side will stop moving (or really really slow down), leaving the high side to continue its downward progress alone.
Even so expect the engineers to declare that the lean poses no structural threat, just arrest it where it stands, and call it a day.
I’ve lived in houses with slightly sloping floors most of my life. It is no big deal.
The Leaning Tower of Pis has a VERY LONG steel cable running from near the top of the tower to a HUGE deadman (concrete foundation – think of a suspension bridge anchorage) VER FAR away. Not feasible in a city.
Be realistic – the Pisa tower also leans a heckuva lot more than Millennium. That’s why there’s a brace. No such thing would ever be needed for Millennium.
Indeed there are so many differences between the structures – height, mass, rigidity, etc. – that a strict…uhm bananas-to-bananas 🙂 comparison would seem to take this out of the realm of theorizing, but for those determined to persist
(and the history of many tried-but-failed efforts that not only failed but actually worsened things won’t give a lot of people here comfort, I imagine).
It wasn’t “architects” that came up with the idea, it was – in the words of M&R – “a pair of engineering firms”; but I have to agree with you: why waste money on hiring (hopefully) qualified engineers when Millennium can get all this useful advice for free ??
It’s NOT the architect. Not.
Read my comment above. Will everyone please educate themselves on what architects do and what structural engineers do? thank you.
You must mean the pile sub’s engineer rather than the building’s structural engineer. SE’s on the design team don’t design deep foundations in my experience, but do provide design criteria based on the building design. After that, it’s up to the geotech engineer and the design/build pile sub.
Regardless, anyone connected to this project with an insurance policy will get to pitch in.
No, what I mean is that architect’s do not design structural systems. Engineers of any and all kinds do.
Don’t see why TJPA should be on the hook for the bill, seeing as the Millennium tilt started before TJPA even started.
Exactly, but if your back was up against the wall and you don’t want to admit guilt/stupidity/penny pinching you are going to try to find a scapegoat. Unfortunately, the TJPA is a convenient choice. Again, who wins? Lawyers do…
So let me get this straight:
-building was heaviest ever built on fill in SF
-started sinking almost immediately, and quickly shot past it’s projected lifetime settling
-Continued to sink at an even rate throughout construction on Transbay center/tower, and has continued to sink since the below-ground portions of those projects were completed
-Proposed solution is to add the pilings they claimed were unnecessary.
Conclusion: Every new fact I learn paints the Millennium Partners in a worse light.
Bingo. And these same greedy developers, who have shown zero sincere concern for the residents affected by their penny-pinching, are busy doing it to other future victims. Why anyone would consider buying any of their product ever again is beyond me.
Yes exactly. Also I would add the sinking and lean was noticed before transbay terminal even broke ground – though at that time if I recall the lean was only 2.5 inches.
The reason for suing transbay terminal, salesforce building, the city, and anyone else that they can think of is so that they can get someone else’s money to pay for their engineering miscalculation.
The 2.5 inches might very well be in tolerance considering the design, size and height of tower. Also, logic suggests that initial settlement would happen with full bearing of weight.
I also think Transbay excuse is a reach when it is all said and done as long as transbay excavation & shoring was done in accordance with acceptable design and practices…believe transbay shoring included those massive longitudinal beams. If anything, the transbay shoring might have provided more support then what the existing soil would have been provided
The developers at end of day accepted the design for the heaviest building yet to be built with that foundation for the known conditions & expected future Transbay construction and or transferred that liability to the designers which might very well be in the contract documents..
Exactly. I suspect that Transbay did perfect of a job shoring up their end with hardly any sinking occurring that side. All the sinking is on the side away from Transbay where no shoring up was done.
Does anyone know the distance from the foundation to bedrock? Add to that the distance penetrating the bedrock for the length of the pile and consequently the needed vertical clearance inside the garage.
Or maybe after the hole is drilled the rebar cage is welded in 20ft segments as it is dropped in the hole and the concrete is poured in place?
[Editor’s Note: Roughly 200 feet.]
Just to chime in on terminology, they are proposing to drill “piers”, not “piles”. Piles are driven, piers are drilled.
As an architect, I want to reinforce Futurist’s comment. The architect is never tasked with designing the structural system, it’s simply not what they’re hired to do, nor their specialty, particularly in a complex project like this.
It sounds very similar to what in Chicago – where squishy soil is normal – is (or was) referred to as “caissons”; but back to the more interesting point: perhaps as an architect you can bridge the gap b/w “Futurist” and “SFDB” ‘s posts. How do you go about selecting an Engineering firm to partner (subcontract) with? It seems like you’ll always be in the old boat of “not knowing what you don’t know.” Is there some kind of referral service within the AIA?
i think the engineering firm is selected by the owner / developer and not the architect (although the owner may be interested in receiving input from the architect).
both the architectural firm and engineering firm work directly for the owner. the engineering firm does not work for the architectural firm.
Perhaps that was the case here, but I was speaking more in general …though maybe you were too. But that system seems fraught with peril: an average person would have even less knowledge on which engineer to pick, I would think.
yeah i was speaking generally but with these large high profile projects, in general they are using top reputable firms with much experience in these types of buildings already, so there is assurance that these structural engineers know their stuff. for a small homeowner who’s looking to hire a mom ‘n pop type of outfit, the best thing to do is to ask to see samples of their work and call the clients for whom they have worked.
David, I’m curious whether Architect would’ve been told that the structure was designed with more cement and less steel, so was told to account for thicker materials. Surely has some some impact to columns, walls, hallways, doesn’t it?
It’s concrete, not cement.
Does anyone know what this is doing to the value of apartments in the building?
On one hand, this news might be good for long term value because there is a fix to the problem. On the other hand, people might have to move out of the building during construction.
At a minimum the parking in the garage will surely be impacted during the work. I would guess that even if they are ‘correcting the lean’ it will go rather slowly and there should be no real need to evacuate units. I would assume that evacuating units would require essentially red-tagging the entire building, which I’m sure they would like to avoid.
Ever heard the term “lipstick on a pig?” Oink, oink…..
I thought i recently read that 160 Folsom not going to bedrock because of the included townhomes.
To belabor the obvious they’re now doing what should have been done in the first place. It’s got to be done even if collapse during a big earthquake is unlikely given potential catastrophic potential not only to MT residents but to the neighboring buildings. There is lots of blame to go around but it’s mainly on MP and the structural engineers (and their soil consultants etc). This is why contractors/engineers charge more for liability insurance. Of course they will try and drag in big pockets like the city and transit authority. Even if they did nothing wrong – other than have bad luck – there is also an element of ‘buyer beware’ and the individual condo owners will likely take a haircut on the valuation and for sure in stress & headache.
I’ve read all the comments above and the one culprit not mentioned in any of the comments above is the obvious one…SFDBI. DBI is supposed to protect the public from faulty construction projects of this size. They are suppose to review the SE’s plans and calculations prior to approving the construction method on a project this size.
I wouldn’t be letting the city off the hook so easily by not placing the blame for this fiasco squarely on DBI.
BTW, this fix should be one for “How did they build that?”. If the underground garage is three stories they will no doubt cut holes between the floors and construct a drilling rig. I assume the rig will be able to drill several piers from one location before being dissembled and moved to a different location. So riddle me this Batman…..are the garage floors post tension? If yes how do they get around all the cables?
Can we use pj Johnston as a bit on the drill?
Or we can ask all the Google engineers to connect floating wind turbines to the tower like images in the movie big hero 6 / and it will steady the building drift // or better yet attach all the Google buses and run em off the piers and sink them into the bay to form a sea wall attached to the buildings top it will look like another bay bridge design tensile mania…
I’m glad they’ve finally reached this conclusion and that they think they can do it.
Regardless, the remedy will take years and years to execute.
An interesting back story would be to be able to listen in on the intense meetings early in the design, between the owners (who had full decision making responsibility, the structural engineering people, the developer, the city and other high level participants. At some point someone suggested that to “save money” maybe we don’t need to drill to bedrock. That had to come up. And someone, or many someones either agreed or disagreed. Ultimately there were specific individuals who made ALL the decisions regarding the construction of this building.
That would be a fascinating discussion to hear. It would ultimately show who is responsible for making the cost-savings decision which is now horribly haunting the building.
Yes it would be fascinating and we can guess how the conversation went.
They took a risk to save money but rolled snake eyes and it should cost them and not the city or transit authority (basically all of us the taxpayers)
This is silly! At the end of the day you are looking at a half billion ($500 million) dollar structural reinforcement. Just tear the tower down and save the money for settlement claims.
as a non-engineer, i can imagine how this proposed fix will prevent further settling, but i can’t imagine how they will force the building back to its correct and fully upright position. not to mention how they’ll account for additional settling that may occur during the course of implementing this fix.
I’m thinking it’s time for a proposition on the ballot. “A giant balloon with the proud visage of Emperor shall be attached to the downwardly mobile side of this edifice to support it in it’s time of need and bring cheer to the citizens living in fear under it’s gloomy shadow….”. Certainly more rational or useful than anything the BOS has done to rectify the issue….
UPDATE: Plan to Fix This Sinking Tower is about to Be Tested
GEOTECHNICAL ENGINEERS design foundations for buildings that STRUCTURAL ENGINEERS design the structure for based on ARCHITECTS’ designs. The DEVELOPER hires this team and works closely with them throughout design and construction.
GEOTECHNICAL ENGINEERS may present a developer/client with foundation options based on variants of cost and risk (low risk/high cost vs low cost/high risk). The developer makes the final decision.
This is a very simple explanation of how many project teams are assembled, intended to help educate some of the “design laymen” in this discussion. I hope this helps.
@ the 1st and Mission construction site active now, it is ~265′ to bedrock, and another 20′ into the bedrock. See you all after the earthquake.
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