SF Tower settlement Part II 18

[1503-44]

"Appreciation has dropped to 2%"
Well that's less than inflation, but more than interest rates.

Although as I said, probably nobody bought in for either of those reasons.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[dik]

I don't think you can do that... but, I understand the peer review of the building, did that. I don't know what the 'point of no return' is, but there is one. Unlike the Florida condo, this will not 'collapse into a heap'. If the soil is that sensitive to pore pressure, I'd be really concerned about liquifaction during a seismic event... fortunately SF rarely experiences these... and the engineers have already investigated this outcome.

With the issues that have come up, my confidence in the protagonists is not at an alltime high.

A more interesting legal issue... do the condo owners face the costs for remedy? I know there was some kind of legal settlement but is there anything that includes proper repair... or can the owners be stuck with the cost for demolition?

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

-Dik

 

[JedClampett]

SwinnyGG, good question that I don't have the answer for. But I suspect that the perception of the tilt by the tenants will be the governing factor, not the capacity. You're never going to convince the residents that place is safe and stable.
Also, as the building tilts, the offending piles will be more heavily loaded, exacerbating the issue. Now eventually the clays will settle all they're going to settle, but I don't think the tenants are going to be patient.

 

[apper.42]

now 22" of tilt at th top

22" sounds like a lot but it is sort of diagonal to the building with most to the north and about half say to the west. So in the 200' depth direction N to S the building leans about 19" or 1.58' / = 0.79' at the midheight assuming the building stays straight with the C of G off by about 0.8 feet. This assumes that the building weight DL + LL is evenly distributed across the width and depth of the building which it probably is not. Different layouts on floors, uneven distribution of mechanical loads, elevator shafts, stairwells could easily throw the C of G off by more. Taking the entire building weight of 224000 kips at an eccentricity of 0.8 feet would result in a moment of 17920 k-ft. The section modulus of the building in the 200 ft direction is (100 x (200^2)) /6 = 666667 ft3. In the 100 ft direction it is (200 x (100^2)/6 = 333333 ft3

Compressive stress on the building footprint is = 224000 kips over 100 X 200 ft2 = 11.2 k/ft2

Compressive stress due to the eccentricity of the building = 17920 kip-ft/666667 ft3 = 0.0268 k/ft2

As you can see the effective stress on the building at the base due to the permanent moment is miniscule in the N-S direction compared to the Dead + Live load given for the entire building. In the E-W direction the moment component would actually be the same at 0.268 k/ft2.

So if I have not made any math errors this much eccentricity is really insignificant at this point in time for the entire building. Increasing rate of settlement could change the story but liquification of the marine clays in an earthquake could suddenly change everything.

 

[dik]

That was my concern early in the first thread... and this had been addressed. With the results of these experts, to date, I'm not as confident.

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

-Dik

 

[dik]

4' sounds a lot less than 48", too... I wonder what the 'cut-off' point is?

With liquifaction, will it sink? Fortunately it can only go down about 200', so you might be able to exit the building at the 20th floor?

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

-Dik

 

[FacEngrPE]

Settlement is not the only potential failure mechanism for piles in soils with a potential to liquefy.

The paper following presents "probable mechanisms of pile failure in liquefiable soils as bending, buckling, shear, settlement or dynamic amplification, and the piles may fail either due to any of the mechanisms or a combination of some or all of them".

Mechanism of failure of three pile-supported structures structure’s during three different earthquakes; Suresh R. Dash Indian Institute of Technolgy Bhubaneswar, India; Subhamoy Bhattacharya University of Bristol, United Kingdom

I wounder what a soils expert thinks about these things?

 

[dik]

No kidding?a

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

-Dik

 

[dik]

Good paper, thanks... I chose vertical translation because it was likely the least onorous to deal with... the existing piles would likely prevent it from going down the full 200'... Maybe you'd exit at the 10th floor?

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

-Dik

 

[geochase]

For all wondering about the liquefaction potential of the soils at depth, the Colma Formation (bearing layer for the original piles) and underlying Old Bay Clay are not considered liquefiable. The liquefiable soils are at relatively shallow depths, comprised of the artificial fill materials near surface, and underlying young alluvium. The young Bay Mud soils are not classically "liquefiable" per se, either, but can be subject to significant loss of strength during shaking. The probability of liquefaction affecting the tower is quite minimal given all foundation loads are imparted to soils well below likely depth of liquefaction.

 

[hamjohn]

Is epoxybot missing?

 

[dik]

Thanks...

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

-Dik

 

[Phil1934]

https://archinect.com/news/article/...epair-halted-after-further-sinking-discovered

 

[dik]

"The “perimeter pile upgrade” project, paid for as part of a confidential settlement reached last year, is designed to reinforce the foundation of the 58-story, luxury Millennium Tower after it had been discovered in 2016 that the northwest corner of the structure had sunk 16 inches since its opening in 2009. Fast forward to 2018, an inspection revealed the building had descended an additional two inches."

I wonder what happens when the confidential settlement agreement doesn't work... maybe the additional settlement was included in the settlement.

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

-Dik

 

[epoxybot]

22" sounds like a lot but it is sort of diagonal to the building with most to the north and about half say to the west.

- Actually the majority of tilt is to the west.

DeSimone's project foundation calculations submittal gives a load of 14.8 ksf for a 106' x 140' piled foundation. The plan view submitted by Lera/ENGEO for the previous solution, the symmetrical piling upgrade, was for the as-built, 103' x 153' piled foundation for 14.58 ksf.

Here is a comment from the 'expert' panel that reviewed the current Perimeter Pile Upgrade for SFDBI. Part of the commentary is in regards to work done by Lera/ENGEO.

Here are a couple of links to articles in Structure Magazine. One by Ron Hamburger of SG&H and another by the Slate geotech people.

I thought the ground profile the perimeter piles will pass through was interesting.

This paper on the Geology of San Francisco gives some interesting characterization to Old Bay Clay and Cloma Sand Hydraulic Coefficient.
...Hydraulic Conductivity:
The hydraulic conductivity of the Colma Formation is generally lower than would be expected based on the
typically fine to medium grain size of the strata. This probably results from the material in the interstitial
space between the sand grains that can contain silt or clay particles, in addition to calcium carbonate
cementation and iron oxide precipitation. Hydraulic conductivity values for the Colma Formation typically
range between 1x10-5 and 1x10-3 cm/s (Johnson, personal communication). While sandy zones at the higher
end of the hydraulic conductivity range are common, the overall character of the Colma Formation is that
it more often exhibits conductivity values toward the lower end of this range.

The hydraulic conductivity of Yerba Buena Mud/Old Bay Deposits strata will depend on the textural variations in the strata (i.e., sand or clay). While the overall depositional setting for the Yerba Buena Mud/Old Bay Deposits was a marine environment resulting in predominantly fine-grained deposits, significant yet discontinuous lenses of sandy material are quite common. As such, the sandy horizons generally exhibit hydraulic conductivity values between 6 x 10-4 and 2 x 10-3 cm/s (Johnson, personal communication). These values are relatively large; however the limited extent of these lenses cause the overall hydraulic conductivity of the deposit to be dominated mostly by the clayey strata where the hydraulic conductivity is typically lower, with values ranging between of 10-7 and 10-5 cm/s (Johnson, personal communication). END

The ground between the Out-rigger Super-Cloumns on Fremont St. seems to be quite complicated. Maybe they should of hired Michael D. Holloway from Insit-u-tech, the Geotech who performed PDA & CapWap on the tower Indicator piles to the 'Expert's' review of the Perimeter Pile Upgrade; since he's the only person who was involved in the 301 Mission Street project that thought the PDA & CapWap showed more ground investigation was warranted.

As for the replenishment of ground water to the general vicinity of Fremont & Mission streets, shoring walls for the Transit Center & Salesforce Tower block Rincon Hill from draining to north toward Mission St., and Mission St. from which is the bottom of an ancient ravine. The Transit Center & Salesforce Tower shoring/cut-off walls, two in each direction, penetrate 5 to 15 feet into the Old Bay Clay. Then, there is the -90' tower/podium shoring wall, without a vertical gradient above -25. The Transit Center & Salesforce tower are underground levies, blocking groundwater recharge.

A proper representation of the piles in profile along Fremont St. shows the shortest spec'd piles, don't reach a sand layer, based on Treadwell & Rollo's original bore logs.

The yellow points represent 2/3rds the pile length, exclusive of the mat.

 

[dik]

Is this what we're looking at? Looks really good for liquifaction...

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

-Dik

 

[epoxybot]

The tower is between Mission & Howard but yeah, they are right over the middle of the ravine.

 

[dik]

A geotekkie may have a better handle on the foundations; I've only done a few seismic projects and none of them where liquifaction was an issue. Doesn't look good from here, and the red box sticks up 3x as high. It's time they got 'the big one',too. I don't know if the building is to scale horizontally... just a WAG.

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

-Dik

 

[spsalso]

Millennium Tower is 645' tall, 150' wide on Fremont Street, and 110' wide on Mission Street. Dimensions approximate.

The proportions of the above ground part of the red rectangle look right to me.

The red rectangle has the below grade part at about 415' deep. THAT seems a goodly ways off.



spsalso

 

[dik]

I thought the piles were only about 100' long, not 400', and that bedrock was about 200' down.

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

-Dik

 

[spsalso]

"I thought the piles were only about 100' long, not 400', and that bedrock was about 200' down."

Ah, I see where I made a mistake. The top of the red rectangle is NOT the top of the building, though it DOES seem reasonable to assume that. Over on the left, there's a height scale, with the top of the rectangle ending at about 200'. So the building got several hundred feet chopped off, so as to fit.

The piles do seem to be the correct length at about 100'.

And since the x and y axes are not equivalent, the assumption that the proportions would be equivalent is incorrect.

The red rectangle's width, however, is incorrect. In the drawing, it is about 500', as opposed to the more correct width of 150'.


spsalso