Don's Home Places California North Central Bay Area San Francisco Millennium Tower
The 58 story Millennium Tower at 301 Mission St. in San Francisco, the highest residential building west of the Mississippi, is sinking and leaning.
It was built in 2009 at a cost of $550 million.
It is sinking almost 2 in per year, 17 in as of 2017 and leaning 14 in.

A two-bedroom condominium on the 42nd floor cost $2.1 million in 2009.
Joe Montana and his wife listed their condo there for $4 million in 2016.

It is concrete instead of steel construction which is makes it heavier.
It is built in an area which was created by bulldozing rubble from the 1906 San Francisco over top of fill created with dredged soil years before.
950 pilings go down 80 ft to get thru the fill material and rest in compacted sand and was approved by the city. They rely on friction along the 80 ft length rather than the sand to hold them up.
Engineers say they should have gone down 200 ft to bedrock.

Millennium Partners, after a long period of silence, told reporters in September that while their own removal of groundwater had been responsible for the initial sinking of the building, the subsequent sinking was caused by the digging next door for the new transportation hub.

Proposals to fix it include:
Permanently freezing the ground below.
Taking down the top 20 floors.
Putting piles down to beadrock (but how?)

In 1970 I worked for Pacific Bell at the old Folger Coffee Company Building at 101 Howard St. a few blocks away.
We watched construction of a new building next door. A pile driver was pounding steel beams down for the foundation. The beams would go down a foot or so with each blow then they would go down about 8' all of a sudden.
We were having problems with a new mainframe computer we installed and brought out the engineers who had designed it. They found that the electrical ground was not sufficient because of the soil there and we had to run a large ground wire thru phone company conduit up the street to solid ground.


Zoom out

Satellites from the European Space Agency confirm the building is sinking. Red dots in the image to the left indicate sinking. See Satellites confirm sinking of San Francisco tower | ESA.int


Gauges measure progress of cracks in the basement.

Links:
San Francisco's leaning tower of lawsuits - CBS News 60 Minutes
In San Francisco, a Sinking Skyscraper and a Deepening Dispute - The New York Times
What Parts of San Francisco are Built on Land Fill?
An engineer’s short, simple explanation of Millennium Tower problem - Curbed SF
Satellites confirm sinking of San Francisco tower | ESA.int
Millennium Tower is Sinking; and Waiting is the Hardest Part | Hackaday


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last updated 2 Nov 2017