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Test Drilling Launched at Millennium Tower

Monday, February 5, 2018

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To address and evaluate a planned fix, an exploratory drilling project is underway at San Francisco’s Millennium Tower, which has sunk and tilted several inches since its construction.

The $9 million endeavor involves drilling holes between 200 and 300 feet down to the bedrock, noted the NBC Bay Area Investigative Unit.

Attempting Solutions

To date, the building has sunk 17 inches to the north and west. The current drilling project could prove to be a way to stabilize the foundation. If this is the case, it may cost up to $150 million to shore up the foundation, even though the entity to pay for the repair remains unclear, due to the ongoing lawsuits surrounding the issue.

Drilling began on Jan. 2, and will continue for the following 10 weeks.

Hydrogen Iodide, public domain, via Wikimedia Commons

To address and evaluate a planned fix, an exploratory drilling project is underway at San Francisco’s Millennium Tower, which is most known for the fact that it has sunk and tilted several inches since its construction.

If the results of both the test and the plan are promising, 100 to 150 holes will be bored through the 10-foot-thick steel-reinforced concrete foundation. This tactic is known as micropiling.

Moving forward, crews hired by the Millennium Homeowners Association will be drilling on weekdays, 12 hours a day.

Previous Investigation

The structure’s sinking and settling has also led to gaps forming in the walls, and in a 2016 investigation, the tower’s housing association hired firm Allana, Buick and Bers to inspect resident Paula Pretlow’s unit, as she and several other residents had complained of “unexplained odors permeating their luxury units," reported the NBC Bay Area Investigative Unit.

To investigate this concern, holes were burrowed through the walls of Pretlow’s unit, with smoke bombs set off below. What resulted was smoke coming up through holes surrounding pipes and ducts. According to Business Insider, these gaps are normally filled with fire-resistant caulking.

At the time, the consultants warned that the openings represented a breach in the fire and smoke barrier of the building, which poses a hazard to residents. If a fire were to occur, flames could jump floors through the gaps.

Those findings, according to NBC Bay Area, had been omitted from the housing association’s report.

Foundation Rules

In response to the Millennium Tower’s ongoing issues, the city and county Department of Building Inspection recently released guidelines for design review for buildings that are 240 feet or taller.

According to Engineering News-Record, the guidelines require an additional member or two for a building’s peer-review panel. These members can either be a state-registered geotechnical engineer or a civil engineer with proven geotechnical experience. Projects located in at-risk areas—where the soil is subject to liquefaction or is in a seismic zone—would require an additional geotechnical engineer on the team.


Tagged categories: Architecture; Condominiums/High-Rise Residential; Government; Health and safety; Maintenance + Renovation; North America

Comment from peter gibson, (2/5/2018, 4:58 PM)

Will somebody please explain how you drill through 10 ft of concrete with a huge building on top of the foundation. Who is this miracle worker. At $150 mn ...whos paying that.

Comment from Robert Bullard, (2/6/2018, 11:23 AM)

Drilling is not the problem. If you know where all the other piles, piping, etc. in or below the 10 ft thick concrete pile cap are located, the resulting 'map' may give you enough room to install a secondary 'deep' foundation. The fun really begins when the secondary foundation is fully installed and the load of the building is progressively transferred by creative jacking to the new foundation, for the pattern of the applied lift forces must not only exceed the weight of the building, but also be sufficient to extract the original piles, thereby not only opening the can of worms of damage to those piles, but also possible damage to the 10 foot thick slab, etc. For those of us in the business, this geotechnical enterprise is more than solving a complex problem over a period of years; it is an adventure.

Comment from Michael Halliwell, (2/8/2018, 12:23 PM)

It's relatively easy to core through concrete, even 10' thick concrete, with the correct diamond bit coring tools. Casting new piles is also pretty easy once you drill down through the cored holes. Robert is quite right, though....once the new foundation is in place, that's when the hard part starts.

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