A legal wrangle is ongoing in the US, where the tallest concrete structure ever constructed in San Francisco is both sinking and leaning.

The 58-storey, 196.5 m Millennium Tower in San Francisco has reportedly sunk 40.6 cm and is currently leaning 19.3 cm off of vertical at the top.

The skyscraper, home to 400 luxury condominiums, opened with much fanfare in 2009, and has won numerous architecture and engineering awards.

The developer of the tower, Millennium Partners, has pointed the finger of blame for the tower’s sinking at major excavation works taking place just a few metres away, where a bus and rail hub is currently under construction.

Millennium Partners says dewatering that took place when contractors began work on the Transbay Transit Center in 2010, caused the sand beneath the Millennium Tower to compact, causing the tower to sink.

Scott Boule of the Transbay Joint Powers Authority (TJPA) – which is a public body – hit back, saying the tilting and sinking of the tower was due “entirely to the failure of the foundation piles for the tower to reach bedrock”.

The tower rests on around 1,000 piles dug some 24 m into the ground. The argument currently revolves around whether this is secure enough from an engineering perspective and why there does not seem to be a paper trail showing when and why the authorities allowed the building to be constructed on packed sand as opposed to bedrock.

As the investigation into any wrongdoing continues, a group of residents from the tower has filed a lawsuit against both Millennium Partners and the Transbay terminal developers to recover losses on their property values.

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