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"

 

[Student Forever]

dik and all,
I took the last cartoon on the "there is no cause for alarm", this is so sad, that even though I tried to have a little humor to move away from the gravity of the situation, it is impossible not to think and worry about the occupants of this and surrounding buildings, and what can happen when the Hayward or San Andreas fault ruptures in Northern California? I hope Peskin will be able to remove the clueless Hamburger+Deierlein pack and bring in knowledgeable experts such as Karp-Karden and Pikes.

 

[dik]

SF: No need to explain...

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

-Dik

 

[hamjohn]

Page 2 of the attached shows the 52-retrofit pile. Which ten have been deleted?

 

[apper.42]

In response to spsalso, here are the Hamburger (non-)responses to Pyke's 2019 comments

Reply to question number 5. is complete bull; the building is probably symmetrical as far as earthquake but the c of g of the building is eccentric to the stiffer resisting piles on the perimeter causing huge torsion in the building in a quake. If we had the exact layout of the external piles we could easily calculate the total torque of the building around the group. We know approximate weight of the building, that it is symmetrical as per Hamburgers own words and we know the approximate g force in an earthquake from hamburgers own spectrum/frequency data so how hard is this to calculate.

To approximate the c of g of the external piles I took a line of piles 150' long on the 153 ft side and a line 100' long on the 103' side with these being about 5' from the edge of the 10' thick pad (cannot find this dimension on the conceptual drawing. This makes the c of g of the pile group about 45' South of the North edge of the pad and about 20' East of the West edge of the pad. Plotting this on a scale dwg. results in the distance between the c of g's varying from a maximum of 43' with the load direction at the maximum distance, 30' with the lateral load in the weak direction 90 deg to the long axis, 31' with the load in the strong direction at 90 deg to the short axis and as little as 0' if the load is along the line btwn the c of g of the building and the c of g of the external pile group.

Torque at the base will potentially be huge and I'm not sure if they calculated the natural frequency of the building in torque which could make things worse.

 

[epoxybot]

The revised pile layout is in page 4. Here

 

[Walnuts]

Thanks to epoxybot who beat me to it. It seems that the reduction in the number of piles might be due more to the presence of existing utilities rather than the performance of the indicator piles? Does anyone know where one can find information on what actually happened with the indicator piles?

 

[dik]

I would think that any repair would have to honour the existing stiffness of the building... to minimise any torsional component.

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

-Dik

 

[Walnuts]

Going back to Hamburger's responses to Pyke, which I posted above. Here is a specific example of obfuscation. First we need to see the prior response in Comment No. 34, which is referenced in Hamburger's first No.1 but was not included.

That text from the Comment Log refers to two figures that were included in Supplement No. 34, one of which is a shear wave velocity profile obtained in a nearby boring for the new bus station:

But in 2018 in the Egan / Slate geotechnical report it is indicated that the shear wave velocity profile that they used for analysis of the site response was as shown below - note the softer top which makes it Site Class E - the input motions for the structural analyses were defined at the base of the perimeter mat but the building code says that site classes are "based on the upper 100 feet (30 m) of the site profile" - the building code generally does a poor job of coping with embedment but that's another story:

And the ERDT signed off on this reply ????

There is a reference in the comment log to an updated geotechnical report in 2019 but I have not seen this and I don't think the shear wave velocity would have been changed. Why? Because another dirty little secret is that the Slate site response analyses were so bad that SGH ended up using the site response analyses, using this same profile, that had been done by ENGEO for LERA! This is noted in the 2018 Egan / Slate geotechnical report and elsewhere.

 

[epoxybot]

Again from LB Karp's "Millennium Debacle" webpage. A letter from SG&H to SFDBI.

SG&H:
...Installation of a first indicator pile, immediately to the west of the building, along Fremont Street,
initiated in early February 2021. As reported in Slate Geotechnical Consultants, 14 May report,
the contractor was unable to maintain the rock socket in an open condition sufficiently long to
allow placement of instrumentation, reinforcing and grout. The contractor proposed an alternative
installation method, using a cased rock socket, which was used to install a second indicator pile,
nearby, and which was successfully tested on 19 April 2021.

 

[Walnuts]

Thanks to epoxybot for the summary of what happened with the indicator piles but has anyone seen the results of the second indicator pile. They cut the number of piles from 52 to 42 based on one load test? I still suspect that the problem with utility locations had something to do with it. That was one of the points that Pyke made back in 2019. To which Hamburger responded "The required construction is neither complex nor unusual". He made no comment on utilities but did say "no dewatering will be required to enable the construction", which was not true. See Slate's monitoring report:

Although the drop in groundwater may not have been nearly as important as the "loss of ground" caused by the way they installed the casings.

 

[Walnuts]

Here is another nice plot from Slate:

So, why did they not put the installation on pause by say the end of June when it was obvious things were going off the rails? Likely they would still be digging themselves in deeper were it not for Jaxon vdB's initial report on NBC Bay Area news.

 

[dik]

Is there a link to the EDRT comments?

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

-Dik

 

[Walnuts]

Dik, the questions posed by the ERDT are attached to their letter to DBI but not the responses. I have a copy of the completed document which has the responses in it but a number of the responses refer to various "supplements", I guess supplements to the SGH 4 volume report. I don't know how much of this is on Larry Karp's web site Link but that's the best source that I am aware of.

 

[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

 

[apper.42]

So, why did they not put the installation on pause...

To put it as politely as I can they are .. the last four letters of your screen name.

 

[dik]

It almost appears that they have no solution on hand and are in a bit of a panic mode...

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

-Dik

 

[apper.42]

Question for
Could they fill the 36" casings x approx 100' with a mixture of 50% scrap steel or scrap iron @ 490 lb/ft3 and 50% normal wt. concrete @ 145 lb/ft3 where the inner casings have not been sunk to bedrock. This would increase the overburden pressure by say 317 lb/ft3 to give a load of = 3.1416 x 1.5^2 x 100 x (317-120) = 139K of added overburden/pile. So 42 piles x 139 k = 139 x 42 = 5838 k of overburden on the lower sides of the building. This is in addition to the estimated 120 lb/ft3 removed as soil and water from the pile boring. Added pressure on the firm layer above the old bay clays would be 19.7 ksf which would tend to push up on the pile group.

Could this assist in to undoing the damage they have done so far with their drilling. Do your geotech thing here for me.

 

[Walnuts]

Sorry apper.42, I think that would make it worse. My own thinking is that they should abandon the Perimeter Pile Upgrade and look at freezing the Old Bay Clay as someone has suggested earlier in the string.

 

[dik]

Do you think it is possible to freeze the soil and while it is frozen, to go in an do a proper piling job?

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

-Dik

 

[apper.42]

Agree that they should abandon the exterior solution but I assume they will at least have to fill the 36" casings with concrete or gravel.

With lensing in clays being so.... unpredictable freezing is risky and so expensive to maintain. I have seen fairly firm clay (shear strength > 1500 psi) in a split basement with water in the lower level where frost heaved and split an 8' high 9" concrete wall and 18" x 5" footing virtually 4 feet vertically at the boundary between the frozen and unfrozen level. I think a majority of the sudden extra settlement was caused by removal of overburden and groundwater but I am no geotechnical engineer.