SF tower settlement 25

[Ingenuity]

...because no one ever hired a geotechnical engineer.

A somewhat misleading quote on behalf of Cubed SF, IMO. A geotech engineer was NOT hired as part of the internal peer-review (which was primarily initiated to look at the structural framing system pertaining to seismic), however the project did have a geotech engineer - namely, Treadwell & Rollo, as part of the project design team.

 

[dik]

Unless Cubed is misquoting Moehle, with the problems encountered, a 'new' independent geotech firm should have been retained to make the report complete and to address any concerns.

Dik

 

[JStephen]

It makes me curious who recommended what. On much smaller projects it is very common to have a geotechnical report that says "You can do it this way, and may have this problem or you can spend more and do it this other way and have less problem", etc. There's quite often a calculated risk involved, and the geotechnical reports I've seen more often reported both options with pros and cons, or went the more conservative route if there was any doubt.

 

[Ingenuity]

If you listen to the testimony of Moehle [Link] City and County of SF Supervisor Aaron Peskin asks Moehle why he did not stamp/seal his internal peer-review report, and also why was he was not an SE.

There was some interesting background information given on the 80 Natoma project in the testimony, which underwent peer-review about the same time as the Millennium Tower project (mid-late 2004).

 

[dik]

Ingenuity:
Good link, and a bit long. It explains why the documents weren't sealed and that the prof wasn't a registered SE. In some jurisdictions, a professional can be held to the same standard if the documents are not sealed. I have to review it again; it appeared that the politician stated that the foundation peer review had been undertaken by the prof and this went unchallenged(53 minutes into the hearing). It appeared that the whole purpose of the dialogue was to distance the city from the problem.

Dik

 

[HENRYZAU]

would appreciate if anyone can provide some information on the ground profile below pile toe, especially clay thickness/depth.

 

[TerryScan]

Millennium Tower's Earthquake Fitness Models May Not Have Been Accurate

http://sfist.com/2017/03/14/millenn...medium=website&utm_content=link&ICID=ref_fark

 

[dik]

from one of the links, "Moehle wrote that "On the basis of my review, it is my opinion that the foundation design is compliant with the principles and requirements of the building code, and that a foundation permit can be issued for this project." The statement is a little confusing because Moehle clearly recuses himself from having any involvement with the foundation. If his statement is correct, he is stating that the foundation is... and, that a foundation permit should be issued.

Dik

 

[dik]

and one of the links from TerryScan's posting:

http://www.nbcbayarea.com/investiga...isco-Troubled-Millennium-Tower-416066263.html

Dik

 

[dik]

Current articles indicate it has tilted 12" and not 2"...

Dik

 

[Ingenuity]

Current articles indicate it has tilted 12" and not 2"...

dik: What is your article source for this 'revised' tilt, and what is the magnitude of the 'revised' vertical settlement?

 

[dik]

The one lawsuit indicated the 12" tilt and there was this news article:

SAN FRANCISCO (KRON) — It has become known as San Francisco’s sinking tower, and attorneys representing those who live in the Millennium Tower are seeking more than $200 million from those they say are responsible for the building sinking and tilting.

The tower is sinking 16 inches and tilting 12 inches at the penthouse level, attorneys said.

Most of the other articles indicate 2" still and are dated a year ago; it is not known what actual measurements have been taken.

Dik

 

[Spartan5]

link:

http://kron4.com/2017/03/29/attorne...-inches-tilting-12-inches-at-penthouse-level/

 

[epoxybot]

Flexural cracking in concrete is very bad. Since concrete has a low tensile strength, reinforcing steel (rebar) is added to increase its ability to carry loads that would otherwise cause it to crack & lose its load carrying ability. Flexural cracking in concrete can lead to bond loss to reinforcement. Considering this is happening at the base of the structure, it is not a good situation. Gluing it back together with a structural epoxy is very slow & expensive. The cracks seen at the surface do not fully represent what might be going on inside the concrete. Fleural cracks can fold back on themselves, creating an interwoven network of cracks that are difficult to penetrate using standard gravity hydraulic injection techniques and require a very low viscosity epoxy with a long working time & exceptional patience & experience by the technicians.

 

[3DDave]

Any problem left ignored long enough will stop being a problem. Sometimes the cessation of one problem causes the start of another, but that's for others to deal with.

I am reminded that the lowest accessible levels in Venice, Italy were at one time second and third floors.

 

[JedClampett]

See linked article. It seems like the this was the solution all the time, but it sure won't be easy.

 

[dik]

Without going to bedrock, I'd be really concerned with liquifaction of the supporting soil.

Dik

 

[hokie66]

Piling to rock is good, but I wonder about their numbers. They are talking about 100 bored piles, each 10" to 12" in diameter. To me, that doesn't sound like the capacity to jack up that building.

 

[dik]

It's OK Hokie... They did the sums on it, just like the original foundation...

Dik

 

[epoxybot]

LERA certainly knows tilting buildings Link
And DeSimone Consulting Engineers can give their project it's own twist on things. Link

Tubex Grout Injected Piling is probably what they are thinking.
Link
Link