Port of Portland Terminal 6 Modernization

The Port of Portland’s container wharf is an active facility and the Port’s primary source of revenue. Because the wharf was constructed in the 1960s and 1970s, it did not conform to the current code seismic standards. In 2000, the Port launched an initiative to upgrade the wharf, but by 2008 when the Port secured funds for the upgrade, further analysis using improved techniques revealed that significant additional ground improvement would be required to bring the wharf up to the code’s standard. The revised design nearly tripled the anticipated cost, putting the overall project at risk.

The Port asked GeoEngineers to determine whether there was an approach that would help the Port preserve federal funding and enable the project to proceed. As the lead seismic planning consultant for the project, GeoEngineers developed a multi-phased, incremental improvement plan that creatively combined the latest seismic modeling techniques with economic analysis. This innovative solution enabled the Port to prioritize specific ground-improvement projects, justify its investments to community stakeholders, meet code requirements and preserve its grant funding.

Approach

Performance-Based Analysis, Better Design Alternatives

Traditional, force-based seismic analysis does not account for the fact that different parts of a facility will respond differently under earthquake conditions, even if they all have the same factor of safety against failure. As a result, seismic improvements made based on traditional analysis are often much more extensive and costly than necessary to achieve a sufficient factor of safety.

For the Port of Portland project, GeoEngineers opted instead for a performance-based approach, using sophisticated 2-D and 3-D modeling and probabilistic risk analysis to determine how much individual infrastructure elements at the Port will move under different seismic conditions and to anticipate how and when the elements will fail. This approach resulted in a much more detailed, site-specific understanding of how different design alternatives will reduce seismic risk.

Targeted Improvements, Improved Return on Investment

GeoEngineers conducted a cost-benefit analysis to help the Port select the improvements that would provide the optimum return for this and future project phases. We worked closely with the Port’s economist and risk manager, who used the targeted risk data to determine the economic impact of various improvement scenarios on the Portland community. This information was included in the final return-on-investment analysis and will factor heavily in the Port’s future long-term capital budget planning.

GeoEngineers recommended upgrades to the Port’s existing berth support structures, a series of sheet pile cellular structures filled with dredged sand. Our seismic analysis determined that the wharf’s performance is controlled by liquefaction of the soil below the original wharf fill.

Accordingly, GeoEngineers designed a series of stone and jet-grouted columns to address this concern. Our innovative replacement technique for the stone columns was made feasible by the reduced conservatism in the design, helping optimize overall construction costs. The 15-foot-diameter jet-grouted columns the team designed are, to our knowledge, the largest in-situ jet-grouted columns ever built.

During construction, GeoEngineers ran field explorations to verify the performance of the stone columns and conducted continuous coring to verify the diameter and strength of the jet-grouted columns.

Results

• GeoEngineers’ performance-based seismic modeling, combined with comprehensive economic analysis, enabled the Port to pinpoint and prioritize seismic improvements, justify its investments to community stakeholders and preserve its grant funding.
• Our highly optimized, lower-cost design met code requirements and reduced overall seismic risk to the facility and community.
• GeoEngineers saved the Port thousands of dollars during construction monitoring by making real-time design adjustments to adapt to changing site conditions and accommodate equipment constraints.
• The Port is so pleased with GeoEngineers’ performance-based approach that it is planning to use the model to evaluate all of the Port’s facilities and to apply the model to port-wide seismic-planning initiatives.
• This sustainable model enables public agencies to make more of their shrinking resources, share their decisions more readily with community stakeholders and demonstrate tangible returns.