The already leaning Millennium Tower tilted another quarter of an inch this month when crews installed the second of a series of test piles, according to newly released data reviewed by NBC Bay Area’s Investigative Unit. Those test piles are part of a proposed fix - meant to keep the building from sinking and tilting more.
The new shift marks the second time the troubled tower has suddenly tilted while crews were testing various methods to limit settlement under the sinking building. The first time, the building tilted a quarter of an inch during the four days a test pile was installed in mid-November, That's according to data released by the city’s Department of Building Inspection.
The tower is currently tilting more than two feet out at the corner of Mission and Fremont streets. It has also sunk two inches at the base just since work on a fix began in May. The proposed fix calls for piles to be sunk to bedrock to help shore up the building on two sides.
NBC Bay Area’s Investigative Unit first reported that a sudden plunge in water levels had been recorded when the first test pile was installed between Nov. 15 and Nov. 19.
The latest data – which was logged during installation of a second test pile on Dec. 1 – reflects an almost identical plunge of about 12 or more feet in water levels.
“That isn’t surprising,” said veteran geotechnical engineer Bob Pyke, adding that the new drop is more evidence of his theory.
That theory suggests the problem is the sucking action created by the pressurized air used to vacuum up water and soil during the pile drilling process. Pyke believes the sucking - which he compared to pulling a milkshake through a straw - likely led to the water depletion and accelerated tilt.
In both the first and second tests, the data shows that while the water rapidly returned in the area of the pile - it did not fully return to the level found at other monitoring sites under the building.
The latest data comes as fix designer Ron Hamburger recently got permission, from the city, to install a third test pile. Hambuger says the three pile tests are all needed to help determine how many piles will be needed to shore up the building along the north and west sides.
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The original plan approved by the city was to install 52, but Hamburger has indicated he believes they could cut that number by more than half. Hamburger has also said he believes the building could tilt as much as 40 inches at the northwest corner before there would be any problem with the plumbing, elevators and the tower's other life-safety systems.
