Voluntary Structural Upgrade of Millennium Tower

San Francisco, California

Slate Geotechnical Consultants provided engineering support to the Geotechnical Engineer of Record for the voluntary structural upgrade of the Millennium Tower located at 301 Mission Street in downtown San Francisco. The fifty-eight-story Millennium Tower is founded one level below grade and supported by concrete piles driven through soft, compressible clay soil to the underlying dense sand layer. The Millennium Tower has settled about 17 inches. The voluntary structural upgrade consists of installation of new piles along the perimeter of the Tower on Mission and Fremont Streets.

Slate worked closely with the Geotechnical Engineer of Record to provide input parameters for the non-linear structural model developed by the Structural Engineer of Record for the project, Simpson Gumpertz & Heger. Specifically, Slate assessed the static and dynamic lateral earth pressures acting on the basement; axial load-deformation characteristics of existing piles and lateral group reduction factors; and development of horizontal earthquake response spectra and acceleration time histories. In addition, Slate estimated the projected future settlement of the Tower following the installation of the proposed new piles.