Transforming Treasure Island and Yerba Buena Island: Redefining Urban Living
The Treasure Island and Yerba Buena Island (TI/YBI) project actively began in 2011 when the City and County of San Francisco entered into an agreement with Treasure Island Community Development (TICD) to become the master developer. This project is an ambitious endeavor aiming to revitalize two iconic San Francisco Bay islands, which served as a naval base from 1941 until 1997. As the largest expansion project of public open space in the Bay Area, and perhaps the most complex project on the West Coast, the multi-phase project seeks to redefine urban living. A vision that was originally created in the 1939 Golden Gate International Exposition, the event for which Treasure Island was built.
Treasure Island Development Group’s primary objective is to execute a master plan in an urban environment, creating a vibrant community in a picturesque setting. The project’s scope includes raising TI, a 400-acre man-made island, by three feet and geotechnically improving it to withstand future earthquakes and sea-level rise. Plans consist of constructing 8,000 new homes, 27% of which will be affordable housing, implementing a storm water treatment system that utilizes park open space to treat urban runoff before it enters the Bay, developing 22 miles of trails, nearly 200 acres of parks and open space and a range of community amenities. The initial two contracts, worth approximately $100 million, were awarded to DeSilva Gates as the general contractor in 2017. These projects included grading and constructing street improvements on YBI, as well as grading and performing geotechnical improvements on TI. In recent phases, DeSilva Gates was chosen to take over as Construction Manager and General Contractor, overseeing civil improvements on TI, constructing numerous parks and open space projects, and performing grading and geotechnical improvements for the next stage of development. In this role DeSilva Gates not only managed the construction of the work but also assisted in design review, agency coordination, quality control oversight, scheduling and access coordination with various vertical developers, as well as public relations with the current island residents and businesses.
Extensive site demolition of existing structures, streets and utilities, and the preservation and relocation of historic monuments, preceded numerous phases and methods of geotechnical mitigation. Monuments from the 1939 Exposition were delicately relocated to their permanent display site at Building One, the historical centerpiece of the islands. Furthermore, crews worked cautiously and carefully to navigate around decommissioned military structures., and to relocate a historic church to a safe location out of the way of planned improvements.
The geotechnical mitigation process began by installing wick drains to a depth of 155 feet below grade to accelerate the consolidation process of the soft bay mud.. Vibro compaction then densified the sandy fill followed by deep soil/cement mixing which stabilized the shoreline of the islands against liquification during an earthquake event. The final phase to stabilize the soil was achieved through numerous surcharge settlement phases, each spanning from two to eight months, which further consolidated and compacted the island soils.
Navigating the project’s intricacies has been a formidable challenge, primarily due to the high density of construction in a tight urban space, surrounded by water. The project team faced numerous logistical complexities, as virtually everything needed for the project must be brought to the islands. Tidal fluctuations (dewatering), frequent traffic pattern changes, narrow roadways, maintaining safe, public access for pedestrians and cyclists, steep slopes, varying soil conditions from hard rock to soft bay mud, a diverse group of local residents, businesses and organizations, a challenging oversight agency (City and County of SF) and other factors added a layer of unpredictability to the project as well.
Notice of Completion was recently issued for the Stage 1 improvements on TI & YBI, signifying a major milestone for both parties. Future phases of the project will build on the foundational work performed to date while keeping a focus on building a connected community. TI/YBI remains a unique and transformative undertaking that will reshape the landscape for the San Francisco Bay islands. The project offers a 360-degree waterfront experience, removed from the hustle and bustle of San Francisco, with stunning million-dollar views of the City, and the Golden Gate and Bay Bridges, Alcatraz and Angel Islands, as well as the North and East Bay hills. The project is well on its way to reestablishing the islands as a vital part of the City, integrating them into the physical fabric and civic consciousness of San Francisco and rekindling the 1939 Exposition’s vision of the future.