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'm pretty sure they would consider that. One advantage is that the passive continuous force required to maintain stability is really quite small.

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

-Dik

 

[Walnuts]

No, dauwerda, they are in a 36-inch casing for about 100 feet, then in Old Bay Clay for another 100 feet, then sands and gravels of the Lower Alameda formation for about 50 feet, then a "rock socket" into Franciscan melange. So, initially like 200 feet unsupported but then the 24-inch pipe piles rest against the bottom of the 36-inch casing, having squashed the soft stuff they inject in between the 24's and the 36's. Seems a bit iffy to me, but I am just a dumb dirt engineer.

 

[dauwerda]

I have not reviewed any technical documents, I just watched the video that I mentioned.
It (the video) states that the holes will be overdrilled so that no part of the new piles will come into contact with the old bay clay. I take this as the oversized casing (36"?) will be installed all the way down to bedrock. The pile itself will fit inside the casing (24"?) and be socketed into the bedrock. The video then states that the annular space will be filled with low strength material - after jacking. This is to ensure no weight is transferred to the clay incidentally through skin friction. If the jacking is happening prior to filling the annular space the pile must be designed for the unsupported length extending from the bedrock to the top of the pile. Are you saying this is not the case?

 

[dik]

The way this has gone, so far, maybe I'm not too confident of that statement...

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

-Dik

 

[epoxybot]

My recollection from the EDRT comment log, is that they will be using an Anti-Friction coating on the lower 24 inch casings, passing through the OBC.

I still don't know how they intend to adjust the tilt with these piles threading through an annulus of about 1/2 inch. If you start at the southwest end of the tower and move to the northwest corner, with incrementally more lift to the northwest corner than to the southwest piles; then skew within the annulus between the pile and the foundation extension is inevitable.

PRACTICAL ENGINEERING used the erroneous 11+ ksf. It is actually 14.8 ksf.

The SFDBI monitoring reports don't look encouraging. The settlement after the 'test' pile looks very much like the settlement leading up to the decision that brought on the perimeter pile work stoppage.

They aren't monitoring the 3 foot cantilever mat, which has hinged from cracking at the re-entrant corner of the 3 foot to 10 foot mats at all. Nor are they monitoring the settlement markers just north of the 3 foot mat. That is just burying your head in the sand where real seismic structural damage is high. This is cracking traveling in the 10 foot mat.

Hamjohn - I've looked at that google maps image before. I don't know what they are doing but there are a number of building services at that location, including sewer, water, fire and possibly electrical.

 

[Walnuts]

epoxybot PRACTICAL ENGINEERING did not get some of the details correct but his 11+ ksf turns out to be correct once you subtract the weight of the excavated soil (25 feet under the perimeter mat and 40 feet under the core) from the weight of the building. This is the correct way to get to 11+ kips, not Hamburger's assuming the pile supported mat and core are 100 x 200 feet, which they are not! I have a friend who asked him about that and, extraordinarily, he defended his calculation by including and perhaps exaggerating the length of the 3-foot cantilever slab. I conclude that he does not understand basic geotechnical engineering, which we have long suspected.

But you are correct about the anti-friction coating on the 24's. What that does to the lateral capacity I don't know for sure, but I guess it reduces what little lateral support is provided by the OBC!

dauwerda PRACTICAL ENGINEERING did a nice presentation for laypeople but it comes up short on some technical issues. The 36-inch casings definitely do not go to rock - they go only to the top of the OBC.

 

[Walnuts]

epoxybot one more thing. I like your cross-section of the 24's going through the mat extension but, while the design team has sometimes talked about "lifting" the NW corner, there is no way that the jacks are going the actually lift the building. The jacks are just to transfer load rather than to cause any movements. If anything moves it will be the 24-inch piles compressing and buckling rather than the building lifting. They have talked about the load transfer relieving the pressure on the OBC which, over time, might cause some rebound, which would lift the sand layer, the existing forest of concrete piles, the mat and the mat extension, which would cause relative movement of the 24's and the mat extension, but I don't know if that will actually happen. What will happen is that the south and east sides of the building will continue to settle. At what point that locks the 24's into the mat extension I don't know. One other thing, someone I know who talks to Jaxon van Derbeken at NBC Bay Area told me that Jaxon would like to talk to you. Not I think on camera but just because you have a lot of good information. Up to you whether you contact him or not.

 

[hamjohn]

 

[spsalso]

Well.

hamjohn has posted a screenshot that says that "...Downtown San Francisco [is]Sinking Slowly Around Millennium Tower".

Wow!

According to hamjohn, the ONLY thing not sinking is our very own Millennium Towers. Else, why would he/she post it?


It looks as though Millennium Tower only needs a slight directional correction to be the last building standing, as Downtown slowly slips into the mud.

Splook!

spsalso

 

[LionelHutz]

Downtown sinking slowly < Millennium Towers sinking fast.

 

[dik]

from NBC news:

https://www.nbcbayarea.com/investig...ower-tilts-quarter-inch-in-four-days/2750189/

"Newly released monitoring data shows that San Francisco’s Millennium Tower tilted a quarter inch during the four days it took to install the first test pile to bedrock last month.

The monitoring data tracks settlement, tilting and water pressure levels underneath the sinking and leaning structure since work began on a fix for the troubled tower in May. Since work began to shore the sinking structure up on the north and west sides, the building has settled nearly 2 inches at the northwest corner and is now tilting more than two feet at that edge."

Maybe time to move on to 'Part III'...

thread815-490007

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

-Dik