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Space Agency Confirms Sinking Tower

Wednesday, November 30, 2016

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It’s been established for months now that San Francisco’s Millennium Tower is sinking, but the latest twist in the story reveals that the subsidence can even be seen from space.

The European Space Agency announced Friday (Nov. 25) that satellite imagery confirms the luxury condo building, built in 2008, has been sinking “by a few centimeters per year.” The agency released the information in association with a program it is involved with that uses satellite imagery to monitor ground movement in urban areas.

Millennium Tower satellite image
Satellite images: Contain modified Copernicus Sentinel data (2015–16) / ESA SEOM INSARAP study / PPO.labs / Norut / NGU

European Space Agency satellite imagery confirms San Francisco's Millennium Tower, built in 2008, has been sinking “by a few centimeters per year.” Red dots indicate areas that are subsiding; green dots indicate areas that remain steady.

The tower, according to a report published in August, has sunk 16 inches since opening in 2008, and tilts about 2 inches to the northwest. Originally, it was expected to settle about 5 inches over time.

Monitoring Buildings from Space

San Francisco and Oslo are two of the main cities being studied in the program, in which the ESA, PPO.labs and the Geological Survey of Norway monitor the landscape and buildings in particular areas using the Copernicus Sentinel-1 twin satellites.

Scientists compare radar scans from the Copernicus satellites to detect shifts in the ground, and especially in buildings, which the agency says “better reflect the radar beam.” The resulting imagery shows where buildings remain stable and where they either have moved away from the radar—meaning they’ve likely subsided—or toward the radar.

The imagery shows movement of just millimeters, though it can’t necessarily account well for tilting.

New Tower Suits

The intercontinental volley is just the latest in a string of bad news for the tower and its developers, Millennium Partners. On Nov. 3, the city of San Francisco filed suit against the developer for failing to tell condo owners and buyers about the rapid sinking sooner.

And on Nov. 15, a pair of condo owners filed a civil suit against not only Millennium Partners, but also the city itself and the Transbay Joint Powers Authority, claiming that the parties all conspired to keep the subsidence secret.

San Francisco satellite image

Scientists compare radar scans of cities like San Francisco (pictured) from the Copernicus satellites to detect shifts in the ground, and especially in buildings, which the agency says “better reflect the radar beam.”

The San Francisco Business Times reported that the suit claims the developer, the transit authority and the city’s Department of Building Inspection all knew of the problem by March 2009, when permits were being issued for the Transbay Center, a transit center under construction adjacent to the tower.

Since the news of the sinking and tilting went public in August, Millennium Partners has laid the blame for the problem on TJPA, which it says undermined the building’s stability with its Transbay Center construction. TJPA, for its part, has argued that the tower’s piles should have been driven all the way down to bedrock, eliminating the subsidence issue.

Concrete Construction

The Millennium Tower is built on a concrete slab, with 14-inch square precast piles that extend 60 to 80 feet down. The tower is built on fill, as it rests beyond where the shoreline of the San Francisco Bay originally was.

Millennium Tower
By Daniel Ramirez – CC-BY 2.0, via Flickr

The tower, according to a report published in August, has sunk 16 inches since opening in 2008, and tilts about 2 inches to the northwest.

When the Handel Architects-designed tower was built, it won awards for its design and structural engineering.

Safe for Occupancy

In October, earthquake-proof design expert Ron Hamburger issued a report concluding that despite the settling, the building was safe for occupancy, and would hold up to an earthquake just as well as any other building in the area.

The developer recently brought in engineers to look at another new building under construction just blocks away, leading to speculation the company may change its plans for that building and drill deeper than originally anticipated.

   

Tagged categories: Architecture; concrete; Condominiums/High-Rise Residential; Developers; Engineers; Laws and litigation; Safety

Comment from john lienert, (11/30/2016, 6:54 AM)

Would a fella named Hamburger just "make-up" predictions about a building that in 8 years (or less) sank more than 3 times what was "predicted for the bldgs. lifetime ........?


Comment from peter gibson, (11/30/2016, 11:47 AM)

Right...what does Mr Fries say about that now.He said " don't worry about a thing" Keep an eye on this one.


Comment from M. Halliwell, (12/1/2016, 11:09 AM)

Yes, the amount of settlement was underestimated....the fill wasn't as consolidated as it should have been for the building and sure, the foundations could have gone down to bedrock...but...the rate of consolidation and settlement decreases with time, so the building has probably seen a substantial majority of its total settlement already (8 yrs out of typically 25 or 30 yrs until things are deemed consolidated). Sure, it may end up about a foot lower than anticipated, but that doesn't mean the building is unstable or unsafe, even in an earthquake.


Comment from Tom Schwerdt, (12/2/2016, 8:49 AM)

Until the main gas supply line shears off from the added stress/bending....


Comment from M. Halliwell, (12/5/2016, 11:22 AM)

Unless they brought it in using a sleeved vertical riser...then they would be fine ;) Other than the operational issues (gas, water and electrical services, access issues like needing to change a slope or add a step, and so forth) it sounds like the building itself is structurally sound...just not in the desired position.


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