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Leaning Tower of Frisco Could Have an Unintuitive Fix

Engineers have proposed driving micro-piles down to the bedrock on one side of the high-rise, then letting the other side continue to sink until the building straightens itself.

April 16, 2018

When you have a 58-story tall condo building that has sunk 17 inches on one side, causing it to lean 14 inches towards another building since it opened 9 years ago, it might seem the common sense thing to do would be to jack up the sunk side to bring the building to level.

Or, maybe not.

Since the MIllennium Tower's sinking problem started to make national news several years ago, condo owners have been seeking both legal and engineering solutions to the building's plight.

The tower sits on a 10-foot thick mat foundation that is held in place by 950 reinforced concrete piles sunk 60 to 90 feet deep into downtown San Francisco's mud and clay hillside. Because those piles were not sunk into the bedrock beneath the mud and clay, the tower has been steadily sinking deeper into the viscous underground.

Legal debates regarding the building's design, inspections, and how great an impact nearby construction have caused the luxury high-rise to sink continue, but apartment owners are nonetheless dealing with noticeably unlevel floors, cracks in walls, water leaking into the 5-story underground parking garage and lower hallways, and sinking property values.

Most importantly, the tower's 1 1/2-foot tilt is causing the outside cladding on the building to gap, which could lead to a disaster should a fire start in a wall. The gaps would create a perfect updraft for the fire and endanger residents.

Some people feel the only way to really fix the tower is to tear it down and rebuild it, but until various lawsuits are settle, that determination won't be made.

Instead, the homeowners association, represented by O’Melveny & Myers, may have found a way to stabilize, if not fix, the tower and stop the sinking.

Engineers have proposed driving micro-piles down to the bedrock on one side of the high-rise, then letting the other side continue to sink until the building straightens itself.

To do this, between 275 and 300 steel and concrete micro-piles would be bored down 300 feet into bedrock under the building's west side - the sinking Fremont Street side. This proposed retrofit would stop the building's listing.

Then crews would wait until the east side of the building sunk enough to become level with the west side. At that point, micro-piles would be bored under the east side to keep the entire building from moving in either direction.

“The engineers are very confident this is going to stabilize the building,” said Vision Winter, a partner at O’Melveny & Myers.

The San Francisco Chronicle writes not everyone is convinced. According to one resident, no warranties have been issued for the proposed plan.

The retrofit is estimated to cost from $200 to $500 million, and could take up to five years to complete. Soil tests have begun and permits are being requested.

Residents of Millennium Tower have been assured by the city's building department that the structure is safe to live in but some are trying to cut their losses and selling their units. It recently came to light that the tower is sinking faster than previously thought.

 

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