Design of the Marine Foundations for the Skyway Project of the San Francisco Oakland Bay Bridge-PDF

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The San Francisco–Oakland Bay Bridge’s new east span required several foundation types because geology and water depth vary along its route. Near Yerba Buena Island, where bedrock and sand are close to the surface, designers used spread footings, driven H-piles, drilled concrete piles, and rock-socketed tie-downs. The suspension bridge’s tower and piers use a mix of rock-socketed and deep driven piles. The long Skyway, built over soft Young Bay Mud and deeper sediment layers, is supported mainly by 2.5 m steel pipe piles driven as deep as 100 m into the Lower Alameda Formation. The Oakland Approach uses smaller steel piles.<br /><br />Site investigations and earthquake demands strongly shaped the designs. Foundations had to carry gravity and operational loads, remain essentially elastic during the extreme Safety Evaluation Earthquake, and limit post-earthquake footing displacement to 150 mm. Designers accounted for both structural movement and soil motions that vary with depth, including the bending these motions induce in long piles.<br /><br />Cost-saving measures included using predictable target pile penetration as the main installation-acceptance criterion, rather than relying on driving resistance as a measure of ultimate capacity. Earthquake analyses also supported displacement-based design that recognized the piles’ end-bearing capacity. On the Skyway, lightweight steel footing frames reduced seismic bending demands, while slightly battered piles helped meet displacement limits and reduced footing size. Vertical piles were preferred where tension demands were high or where a more ductile response was important.<br /><br />Construction planning emphasized reliable installation and contractor flexibility. Hydraulic hammers, standardized pile sizes, temporary support and guide systems, and early pile-driving demonstrations helped manage installation risks. Testing also established how pile capacity increased as soil resistance recovered after driving, reducing uncertainty for construction loads applied soon afterward. Overall, the foundation designs balanced site geology, seismic performance, buildability, and cost across the bridge’s varied structures.

Keywords

San Francisco-Oakland Bay Bridge

foundation design

deep foundations

earthquake engineering

steel pipe piles

soil-structure interaction

Skyway

Young Bay Mud

pile driving

seismic performance