Geotechnical Evaluation for the Treasure Island New Ferry Terminal Foundations

Treasure Island is located in the center of San Francisco Bay, between the active San Andreas and Hayward faults. Treasure Island was constructed in 1930s at the site of the Yerba Buena Shoals, a shallow-water area directly north of Yerba Buena Island, a natural island. It was constructed from sand fill dredged from the surrounding shoals, placed within perimeter rock dikes. The first phase of the Treasure Island redevelopment included (i) geotechnical ground improvement for 40 acres of land, 3,000 feet of shoreline, and a causeway that connects Treasure Island to Yerba Buena Island, (ii) construction of new infrastructure, (iii) preparation of building pads for mid-rise and high-rise buildings, and (iv) construction of a new transit hub with a ferry terminal, ferry pier, floats, and a breakwater A comprehensive geotechnical investigation was conducted to evaluate the ferry terminal site seismic and geotechnical hazards and provide foundation solutions for the near-shore and off-shore structures. The main geotechnical hazards include the presence of soft marine soils, strong seismic shaking, seismically induced soil liquefaction and lateral spreading, seismic shoreline instability, and kinematic loading on off-shore deep foundations. Deep foundations of the ferry pier, floats, and breakwater were designed to carry kinematic loads due to lateral spreading of the liquefiable offshore soil layers and for the effects of the soft marine deposits. In addition, the design of the ferry terminal at the shoreline included the evaluation of seismic stability of the ferry terminal abutment founded in an area that received deep soil mixing ground improvement. This paper details the geotechnical evaluations and mitigations for the various ferry terminal improvements.