San Francisco's Millennium Tower is sinking say experts
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Millennium Tower, San Francisco

San Francisco's Millennium Tower is sinking say experts

The tallest residential skyscraper in San Francisco is tilting and sinking, according to reports.

Since completing in 2008, the 58-storey Millennium Tower has sunk 16 inches (41 centimetres) and tilted two inches (five centimetres) to the northwest, reported the San Francisco Chronicle.

The most recent analysis was done by an independent consultant hired to monitor the problem at the residential high-rise, which boasts some of the city's most expensive apartments.

A study of the site conducted by engineering firm Arup in 2010 found that the tower had already sunk 10 inches (25 centimetres).

Skyscrapers commonly settle slightly after construction, but the Millennium was only predicted to drop six inches (15 centimetres) during its lifetime.

Millennium Tower developers have blamed construction of the nearby Transbay Transit Center on the building's subsidence.

"They built a half-mile tunnel 60 feet underground and next to our building, and they were supposed to [protect the Millennium] – and they didn't," Millennium Partners spokesperson P J Johnston told Chronicle columnists Matier & Ross.

But the Transbay Joint Powers Authority (TJPA) claims that Millennium Tower builders only sunk piles 80 feet deep into sand – rather than the 200 feet into bedrock – to cut costs.

The organisation reportedly spent more than $58 million (£44 million) building "an underground buttressing system to shore up the Millennium before beginning excavation in 2010", which caused the budget for the transit centre to soar over $2.4 billion (£1.8 billion).

TJPA said it bears "no responsibility for the tilt and excessive settlement" of the Millennium Tower.

Located in the Yerba Buena district, the Millennium Tower was designed by US firm Handel Architects. It is currently the tallest residential building in San Francisco, and the city's third tallest overall.

The Transbay Transit Center Project by Pelli Clarke Pelli Architects encompasses a transport hub, six million square feet of office space and 4,000 residential units, along with the 61-storey Salesforce Tower.

It forms part of a swathe of development across San Francisco, including proposals by OMA, Studio Gang and Foster + Partners.

Image is by Instagram user adamsusaneck.