The team of team of Malcolm Drilling (specialty contractor), Arup (structural and geotechnical engineer) and Brierley Associates (support of excavation designer) has been named winner of this year’s Outstanding Project Award by the Deep Foundations Institute. The team was recognized for 181 Fremont Tower, a mixed-use high-rise under construction in the urban core of the South of Market District of San Francisco, Calif.
The award will be presented at the 43rd Annual Conference on Deep Foundations in Anaheim, Calif., October 24-27, 2018.
Freemont Tower consists of 56 above-ground floors with the roof level at approximately 700 feet above street level. It features an architectural spire that tops the building out at just over 800 feet, making it the second tallest building in San Francisco. The team squeezed the tower into a limited site measuring about 130 feet by 140 feet. It has an open floor plan that incorporating exterior mega-cross-braces to provide lateral stability against seismic and wind loading.
The structural design created a challenge for the building’s foundations because the seismic loads are concentrated in the building’s corners. Drilled shafts with a diameter of 5 to 6 feet were built as deep as 260 feet and socketed as much as 25 feet into the Franciscan Complex bedrock. An additional challenge was the variability of the bedrock. Depth to the bedrock on the east and west ends of the site differed by as much as 14 feet, and the composition of the Franciscan Complex is very irregular. In addition, a watertight, stiff temporary support of excavation system was required to allow the excavation and construction of a 5-level basement that extends to about 60 feet below the surface. The support system guarded adjacent structures, including a 27-floor tower to the east, a 3-story masonry building to the south, and the deep excavation for the Transbay Transit Center to the north.
The OPA was established in 1997 to recognize the work of DFI members. Projects are selected by a committee based on size, scope and challenges; the degree of innovation and ingenuity exercised; and the uniqueness of the solution to the difficulties of the job.
The DFI is an international association of contractors, engineers, academics and suppliers in the deep foundations industry with more than 3,300 members worldwide. For more information about the Deep Foundations Institute, visit www.dfi.org.