Soil Liquefaction Remediation of the Port of San Diego’s B Street Pier Facility Using Deep Soil Mixing

The Port of San Diego’s B Street Pier facility (Pier) is the busiest cruise terminal in the City of San Diego with over a hundred ship calls annually (pre-COVID). The Pier is an approximately 9.4-acre bulkhead faced mole extending about 1,000 ft into San Diego Bay and approximately 400 ft wide. On the three offshore sides of the bulkheaded mole are marginal pile supported wharfs constructed in 1923. The upland side of the mole is a concrete gravity seawall constructed in 1900. The mole soils consist of hydraulically placed dredge spoils and are susceptible to liquefaction.The existing Pier containment walls are deemed inadequate for seismic loading, mainly due to the presence of liquefiable materials both in front of and behind the existing containment wall. A solution consisting of an improved Deep Soil Mixing (DSM) zone coupled with the installation of a new steel sheet bulkhead was selected to retrofit and upgrade the Pier to current seismic standards. A key aspect of the design was to minimize loading induced from the wharf onto the existing curtain wall during an earthquake. The DSM zone is intended to serve a triple purpose, that is to improve shear strength of the soils behind the curtain wall, to mitigate the impact of liquefaction, and to provide sufficient bearing for potential future lightly loaded structures which may be constructed on the Pier. To obtain a cost-effective design and limit the DSM zone extents, the design also needed to limit the seismic load contributions to the DSM from the marginal wharves during seismic conditions. A development plan consisting of a multi-phased construction plan was determined to meet the Port’s capital improvement needs and budget. Phase I development will install the DSM zone and steel sheet pile bulkhead along the south and west face of the mole. Future work will include wharf pile and deck replacement along with completing curtain wall replacement along the north face of the mole. This paper presents the geotechnical design challenges and considerations associated with the design of the DSM and sheet pile system comprising Phase I of the development plan. Key aspects of the geotechnical design included the selection of appropriate liquefaction resistance of the DSM improved zone, designing for the lateral spread of the slope in front of the curtain wall, assessment of stability and deformation of the proposed sheet pile, and the determination of the seismic earth pressures.