C+S June 2022 Vol. 8 Issue 6 (web)

From a World’s Fair to a Local Neighborhood: The Transformation of Treasure Island By Luke Carothers

The original island of the pelicans in the San Francisco Bay, Yerba Buena Island sits between San Francisco and Oakland, California. The first lighthouse was built on the island in 1875. During this time, locals used the island to raise goats–for which the island was renamed for a time–and the military soon found use for the space, establishing a naval training station in 1900. A few decades later in 1936, President Franklin Delano Roosevelt ordered the US Army Corps of Engineers to begin dredging the bay to build a new, 400-acre island on the shoals of Yerba Buena, which had previously represented a shipping danger. Named for the gold that potentially lies in the mud dredged up from the bay’s floor, Treasure island was originally constructed for two pur- poses: to host the 1939-40 Golden Gate International Exposition and serve as a future second airport for San Francisco’s growing population. Several permanent structures were erected on the new island including “Building 1”–a 1938 Art Moderne building–and the terminal building meant to house and showcase new Pan American Airways Clippers. After the Golden Gate International Exposition ended, plans to use the development as a new airport fell out of favor and the Navy began using it as a major training station for World War II all the way through the Cold War. In 1997, the naval station on Treasure Island was closed, and the hangar buildings were converted for other uses such as sound stages for television and movies. Since this time, Treasure Island and its neighbor Yerba Buena have maintained a population around 2,000 residents. In addition, Treasure Island is home to several restaurants, schools, arts and athletics organizations, and a Job Corps campus. Now, both Yerba Buena and Treasure Islands are poised to return to a similar level of prestige that came with the Golden Gate International Exposition. The Treasure Island/Yerba Buena Island Development Proj- ect has plans to create a new San Francisco neighborhood with homes offered at below-market rates, extensive parks and open space, public art, hotels, restaurants, and other elements that would make the develop- ment an ideal destination for both San Francisco residents and tourists alike. To manage this development, the Treasure Island Development Authority (TIDA) began the planning stages of the project around 2011. From a geotechnical perspective, building a new development on top of an island that was dredged from the bay’s floor over half a century ago was a tricky endeavor. To lead the geotechnical work on the develop- ment project, ENGEO started studying the island in 2003. ENGEO, one of the most comprehensive geoscience firms in the world, is serving as

the Geotechnical Engineer of Record. As such, they have been working in a number of areas throughout the different phases of the project, doing everything from conducting the design-level geotechnical study to designing and overseeing a massive ground-improvement program, to designing new building foundations to providing construction-phase quality control, to setting up a Caltrans-certified materials testing lab on the island. The plan for the development on Treasure Island/Yerba Buena Island was to develop approximately 200 acres on Treasure Island and over 85 acres on Yerba Buena Island. Development will include a new ferry terminal, 8,000 residential units, and over 100 acres of parks and open space. However, to begin any sort of large-scale development on the island, engineers had to quantify how the land would perform from load- ing related to new buildings and earthquakes. In 2014, 2015, and 2016 ENGEO conducted full-scale field tests and design-level geotechnical studies to support the first phase of development. Uri Eliahu, ENGEO’s President and CEO, notes that these first geotechnical studies were critical to understanding how the island would perform over time. Eliahu points out that, while the entire island has experienced some degree of settling, it is by no means uniform in distribution. The average settlement across the island since it was constructed is between 6- and 6.5-feet, but, on the north end of the island, the settlement is closer to 10-feet. This is contrasted by the south end of the island, closer to Yerba Buena, that experienced only about 3-feet of settlement. This contrast in settlement is due to the varying materials at different locations. Closer to Yerba Buena, Treasure Island rests on not only the sand pumped up from the bay, but also natural shoals that provide an additional source of stability. At other locations on the island, the soil rests on highly compressible natural bay mud, which, according to Eliahu, makes building on the island a much more involved technical



June 2022

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