The San Francisco Chronicle and Construction Dive both report that engineers may have found a way to slow and stop the Leaning Tower of San Francisco, Millennium Tower’s gradual sinking into the ground.
We have been following this story for some time to see what might happen and how the major parties, now involved in several mediations and lawsuits, address the issue.
The original building was built over a landfill in downtown San Francisco. The design team, consulting engineers, developer and contractors drilled 900 piers to support the original structure. While there are several strongly contested factors that have contributed to the lean, one of them seems to have been that the piers were extended to the 61-90 foot level rather than to bedrock 200 feet below. Adjacent construction of a transit center and dewatering activities caused the 58 story building to sink and lean at a much faster rate than any of the structural models predicted.
Now the engineers are proposing that the “responsible parties” whether the developers, the City of San Francisco, or The Transbay Joint Powers Authority, the public entity building the Eastbay Transit Center on the site next door, drill another 50-100 piers down to 200 feet and bedrock to stop the leaning and stabilize the building.
The estimated initial cost to drill the piers and to level the building would range somewhere between $100 and $150 million. Original predictions were that the repair might cost as much as $1 billion.
Thus far, according to the city Administrator’s office, no one has filed for permits to do the repairs that the LERA firm and DeSimone Consulting Engineers have outlined and because of the legal battles swirling around the project, none of the principals are talking.
There is one small problem though that might cause some concern for the residents of the “tony” condominium project. According to the latest measurements taken by the Arup Group, the building has sunk an additional inch in the last seven months. Additionally there is cracking in the basement, likely from the torque of the building sinking on one side.
Some reports indicate that the residents could likely continue to live in the building while the repairs were undertaken. That assumes that the repairs get underway in a timely fashion and as you might imagine with all of the “finger pointing” litigation and threatened litigation underway, no one is predicting when the major repairs might get underway. The accelerating pace of the “sink and lean” will soon become a major concern for the residents and developers in the earthquake prone City of San Francisco.
We will continue to monitor this one to see whether the engineers and contractors can stop the lean and correct it. According to the Chronicle article, residents are getting a tax break, but not nearly enough to offset the loss of value caused by the defect.
