Millennium Tower in San Francisco is a 58-story luxury condominium building.
A geotechnical report predicted it would settle only 4 to 6 inches over its entire life.
By 2018, the settlement had already reached 18 inches (46 centimeters).
That is three times the upper end of the forecast.
And the building did not settle evenly.
Measurements in 2022 showed a lean of 28 inches (71 centimeters) at the roof.
What gives under that weight?
A deep clay layer sits under the tower. The building's load compresses that clay. A long-term drop in the groundwater level, caused by construction on this and neighboring projects, makes the compression worse.
For the homeowners, the damage led to a lawsuit involving the developers, the city, and the teams behind neighboring projects.
In the repair, new piles — deep supports driven under the building — take about 10 percent of its total weight. After those piles were loaded, measurements showed some return toward vertical, but less than the model had predicted.
The repair changes how the weight travels downward.
It does not straighten the whole tower by itself.
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