Engineers may have hit on a way to prevent Millennium Tower, also known as the Leaning Tower of San Francisco, from sinking into the ground.
The sinking skyscraper was constructed over a landfill site in the city’s downtown area. The developer, together with the design team, consulting engineers, and contractors, drilled 900 piers to reinforce the original structure.
One of the factors that allegedly contributed to the lean is that the piers reached a level of 61 to 90 feet instead of solid bedrock 200 feet below the surface. When dewatering activities and construction of a transit centre took place nearby, the 58-storey building began to lean and sink at a faster speed.
DeSimone Consulting Engineers and the Lera firm are proposing that the parties responsible drill another 50 to 100 piers down to the bedrock to stabilise the sinking skyscraper from further movement. It remains to be seen whether this duty would fall to the City of San Francisco, the developers, or the Transbay Joint Powers Authority that is building the transit center.
Drilling the piers and levelling out the tower will cost an estimated $100 to $150 million, which is substantially less then earlier estimates of $1billion.
The city administrator’s office has confirmed that no one as of yet has filed for the permits needed to carry out the recommended repairs, and because of the legal issues surrounding the project, none of those immediately involved are making a statement.