Unfortunately, while the plan was approved and enacted, work had to be halted last August as it was discovered that the sinking had intensified even with stabilization underway. Simpson Gumpertz & Heger called for 52 new concrete-and-steel piles to be drilled 250 feet into the bedrock below, which would alleviate compressive force on the northern corner of the site and stop both the tilt and sinking. Whatever the cause, the stabilization plan was intended to course correct the tower, which has tilted 26 inches west at the top since its opening. (Courtesy Millennium Towers Homeowners Association) The Perimeter Pile Upgrade includes the drilling of 52 new steel-and-concrete piles along two elevations. This isn’t an uncommon construction method in the Bay Area (and sections of downtown San Francisco are sinking at about three-quarters of an inch every year) and the Millennium Tower design team still maintains that the building’s issues stem from soil compaction caused by the construction of the adjacent Salesforce Tower. The issue stems from the building’s foundations-it sits on a 10-foot-thick concrete pad that it itself is supported by nearly 1,000 reinforced concrete piles driven 90 feet into soft clay. The 645-foot-tall, 58-story tower was completed in 2009 and has been tilting and sinking ever since it opened.
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