The One Marina site rests in the south bay region of Redwood City northeast of Highway 101. This site is in the area of Bair Island, right on the bay shoreline. The site and surrounding area were originally tidal marshlands with meandering sloughs and were filled and diked in the early 1900s. The main problem for the project is settlement and stability of a 10 to 15 foot thick layer of soft clay (bay mud) that is below 10 to 15 feet of old fill. Both foundation support for new structures and seismic slope support next to the bay were solved by Farrell with the Drill Displacement Pile (DDP) system. The DDP work included the support of two 4-story condominiums on the bays edge and the seismic buttress support of soft clay slopes adjacent to the bay for the whole development.
The soft clay shows up at a depth of about 10 feet and extends to a depth of about 20 to 25 feet. The DDP were designed in collaboration with Langan Treadwell & Rollo and KPFF. The design resulted in DDP that extend to depths of 45 to 50 feet below grade. Farrell installed 16” and 18” diameter DDP for foundation support of the structures. In addition to structural foundation support, Farrell installed 24” diameter DDP with full length spiral steel reinforcement to gain the bending action in the old bay clay below the soft clay. Farrell also installed the reinforced concrete grade beam to connect the tops of the slope buttress DDP and the retaining wall at the shoreline. The project was performed during the winter. Managing the bay tide was a challenge at times, but the project was completed on time and within budget.