After three successful pilot casing installations using revised procedures intended to fix the ailing perimeter foundation upgrade at the troubled 645-ft-tall Millennium Tower in San Francisco, Shimmick Construction Co. began installing a pilot pile inside the first casing—also using modified methods. The foundation team developed the new procedures after the remedial work, intended to correct some 17 in. of tower settlement, had instead accelerated settling and tilting by 1 in.
Casing work stopped during the work on the pile, which required many moving parts “to come together,” including repositioning the equipment on site and installing more vibration monitors, says Ronald O. Hamburger, a senior principal with Simpson Gumpertz & Heger and the engineer-of-record for the $100-million fix, likened to putting a bumper jack next to a flat tire.