Wharf Deepening Enabled by Modern Analysis Techniques

The Port of Portland, in Portland, Oregon is dredging several berths at Terminal 6 to take advantage of deepening the lower Columbia River ship channel for larger ships. The terminal’s container wharf is supported by a series of 65-foot diameter steel cellular sheet pile cells and connecting arcs. Previous engineering studies using classical analysis methods determined the existing structure could not be deepened without adding significant structure such as new crane beam piling. Using advanced numerical soil-structure-interaction analysis, a design was developed that achieved goals at lower costs. These numerical analyses were based on back-calculated soil parameters from wharf deformations measured during construction. Numerical modeling forecast deflections for deeper dredged depth, seismic load performance, and showed how the soil and steel sheet piles share the vertical crane loads. The numerical analyses indicated that deflections would be limited to acceptable values, even though the classical analysis resulted in very low factors of safety based on “conventional wisdom”.