Seismic foundation design for Girard Road undercrossing, Presidio Parkway Project, San Francisco, California

摘要

The Presidio Parkway Project in San Francisco, California includes bridges and undercrossing to span the realigned Girard Road. Geotechnical issues including soil liquefaction, lateral spreading and post-liquefaction ground settlement pose significant challenges to the bridge foundation and undercrossing construction. In addition, foundation for the undercrossing has to overcome significant uplift pressures from groundwater and liquefied soils. To address the geotechnical challenges, a foundation system consisting of drilled concrete piers in combination with deep soil mixing ground improvement was adopted. The finite element program, PLAXIS~(3D), was used to evaluate the foundation performance subjected to various static and earthquake load demands. The foundation system including drilled piers and deep soil mixing elements were explicitly modeled. Analytical results indicate that the composite foundation system satisfies the project performance criteria and maintains global stability under both static and earthquake loadings.