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SF Tower settlement Part III 18

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dik

dik

Structural
Apr 13, 2001
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Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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Many thanks to epoxybot for all the detail and especially this: Since the tower’s foundation was mechanically connected to the shoring wall during the tower’s construction and it didn’t show any signs of settlement; SGH seems very optimistic that the shoring wall will indeed settle. From the 13th floor to the 42nd floor, 56% of the building weight was incrementally added to the tower, at approximately 3 million pounds per floor, per week. When the tower was released from the shoring wall, tower settlement accelerated dramatically until the topping off ceremony. There are complications, like the western garage shoring wall being tied in some way to the other shoring walls by the stout diagonal bracing as the garage excavation was being made, and now being stuck in some way to the garage wall because a bond-breaker was never installed, and the fact that the Old Bay Clay would not have been pushed back on to its virgin curve until the Tower got up somewhere approaching its full height, but Hamburger's 2019 assertion that the mat would just push the shoring wall down when they came in contact was very cavalier, and the fact that the ERDT signed off on this suggests that they were asleep at the wheel. Oh, wait a moment, they did recommend in their letter signing of on the Perimeter Pile Upgrade that they be retained for 10 years to monitor it. Maybe they were wide awake?
 
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"...as the tower settles to the east."

That is quite unsettling to read! But at least I know which part of downtown SF to avoid.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
 
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From NBC news, January 7, 2022:

"The 58-story, 645-foot tall tower — opened to residents in 2009 — is now tilting 26 inches north and west at Fremont and Mission Streets in the heart of San Francisco’s financial district..."


There seems to be some confusion as to which direction the damn thing is going to fall. I'd recommend staying out of the Financial District altogether. And also the Embarcadero. City Hall and SF Building Department, on the other hand, are quite a distance away from the drop zone; so the folks there will be safe.


spsalso
 
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@epoxybot

One aspect I've been looking into was construction of the TTC buttress wall re-initiating settlement of the MT. Given the problems SGH has had with installation of the new piles accelerating settlement again, construction of the TTC buttress could be linked as well. The attached Desimone/T&R log scale shows end of primary consolidation may have been approached but resumed after buttress construction. This problem could have been exacerbated by the CDSM shoring wall NOT being complete due to the PGE vault relocation between Fremont/Mission as discussed in the attached ARUP/BF documents. BF/ARUP proceeded with dewatering and ARUP emails show piezometers levels were lowering the groundwater beyond those in the HSI dewatering analysis. I think the big takeaway is everyone who has touched the project underestimated the OBC, especially T&R pushing the OBC back into a normally consolidated state.

TR_Log_Scale_Settlement_luka0x.png
 
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Slide #11 is telling... The Tower of Pisa was tilting as it was being constructed... there is some real intesting history there.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik
 
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(18) Each column will support 1 million pounds instead of (52) 800,000 pounds, although they are rated to take up to 2 million pounds, Hamburger said.

The outside panel of structural experts wrote in their recommendation that in the long term, by 2060, the 18-pile plan could recover about 4.3 inches of westward tilt and 0.3 inches of northward tilt. In contrast, the 52-pile plan was estimated to recover about 5.5 inches of westward tilt and 3.5 inches of northward tilt during the same time.
 
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We'll have to wait and find out if it works... [ponder]

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik
 
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Well, we can visit the tilt-o-meter and see how things are going. I do note that the north-south tilt appears to be currently stable, while the east-west is increasing. This is good news, as it appears it would tend to correct the aim towards the Sales Force Tower.

spsalso
 
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S.F.’s leaning Millennium Tower one step closer to stabilizing its issues

A revised plan to arrest and rebalance the sinking and tilting of San Francisco’s Millennium Tower moved closer to getting the official sign-off after an outside panel of engineers recommended it to the Department of Building Inspection. If all goes as planned, the work could be implemented by the end of the year.

The plan uses 18 instead of 52 piles, or columns, to take some weight off the building’s foundation and stop it from settling further at the building’s northwest corner at Mission and Fremont Streets. Casings are sunk into the deep rock bed below and the piles are then drilled through them to embed 40 feet in the rock.

Project engineer Ron Hamburger of Simpson Gumpertz & Heger said in an email that “all 18 structural piles have been installed” as of March 9 under the originally permitted plan to install 52.[pre][/pre]
 
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Hah, hah, hah, hah! One step closer to not solving the problem. It is not clear to me that they will get much if any rebound when they transfer some of the load to the new perimeter piles, and even their predicted rebound is less than the additional settlement that they have caused so far, let alone any additional settlement that results from the excavation needed to construct the mat extensions.

Mealy-mouthed excerpts from the letter from the EDRT:

Based on our review, these analyses and design calculations conform to accepted engineering practice in accordance with the San Francisco Building Code. [IMHO the problem is complex and unique and is in no way covered by standard engineering practice.]

Based on our review of the drawings and analysis reports provided to us by the EOR and his team, in our professional opinion the revised 18-Pile PPU meets the requirements of section 403.9 of the
2016 San Francisco Existing Building Code. [If you read 403.9 you will see that it is about voluntary seismic retrofits - there is nothing in it that applies to this problem!]

Subject to continued monitoring of the building settlement and tilt, through construction and following completion of the 18-pile PPU, we see no technical reasons to withhold approval of the proposed revisions to the building permit for the voluntary foundation retrofit. [The EDRT previously recommended that they be retained for 10 years to observe the performance!] [Note that they now call it a voluntary foundation retrofit, so 403.9 is not applicable!]

The Tilt-O-Meter seems to be on the blink again!
 
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Walnuts said:
[If you read 403.9 you will see that it is about voluntary seismic retrofits...]
Click to expand...

You called their bluff and read the Building Code. Bet they didn't expect anyone to actually do that!

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
 
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Well, started and then kind of stopped. They have installed every second pile for the secant pile wall(s) along Fremont Street and then switched to Mission Street. It appears that no-one who is willing to speak knows why, but they were approaching the 3-inch limit on westward tilt for the year that the design team had themselves proposed.

202203220578.301Mission.InspectionReport_001_tzizky.png
 
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Note that the DBI inspection report starts at the bottom of the page and reads up!
 
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Am I missing something here?

Clipboard01_bvuaet.jpg


The date occurring before the date of the report?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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Dik, I don't see a date on the report. It has a disposition (start) date and an expiration date, but the report itself is not dated.
 
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Ha! That is a puff piece that sounds like it was written by Hamburger!
 
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