Ever since the Millennium Tower’s chronic sinkage became front page news, San Franciscans have been throwing around the word "bedrock" more often than the cast of "The Flintstones." Suddenly, it’s a hot topic: Does your building go to bedrock? If not, then why?
Previously, only a handful of engineering wonks paid attention to such things, but we could very well be living in a watershed moment when even casual homebuyers start to become a little more foundation savvy.
The developer behind (or underneath, perhaps) the embattled building, Millennium Partners, finally announced that their next building in the city, a high-rise at 706 Mission Street that will serve as the new home of the Mexican Museum will indeed drill down all the way to the bottom (as the San Francisco Chronicle reported and as a Millennium spokesperson confirmed when we asked).
Previously, company co-founder Chris Jeffries always insisted (correctly) that there are any number of buildings in the city with Millennium’s same foundation design—columns sunk into sand and supported by the friction of the building’s own weight. He also said "the state of the art is not to go to bedrock"; which is a debatable position, but at least not obviously wrong either.
The about-face is presumably a PR move: If the Millennium mess is still going on when the new building opens (and, short of the timely discovery of a magic lamp, it will be), potential tenants are going to want extra reassurance that the new tower won’t have to tolerate any tilting.
(For the record, Millennium Partners spokesperson PJ Johnston says that the decision is due to the "unique soil composition at this specific site.)
If this keeps up, we may never see another friction-pile foundation in the city for generations, possibly every. Which is probably a good thing: Although there’s nothing wrong with the principle behind such a design and it works just fine in most buildings (including many here in the city), it’s still true that a bedrock foundation would have saved Millennium Partners their present predicament, regardless of whose fault it turns out to be.
14,000 pounds per square foot of prevention yields an awful lot of cure.
- Tower Developer Rethinks Next Plans [Chronicle]
- Millennium Says Water Table To Blame [Curbed SF]
- Mexican Museum [Curbed SF]
- Engineer’s Simple Explanation of Millennium [Curbed SF]