PORT MAINTENANCE
A properly selected and applied coating provides a physical barrier ... However, coatings should not be considered infallible.
As a result, protecting a sheet pile wall often requires a multi-zone strat- egy, rather than treating the entire structure as if it were exposed to a sin- gle environment. Coatings: The first line of defense For new sheet pile installations, the first line of defense should always be an appropriate protective coating. A properly selected and applied coating provides a physical barrier between the steel and its surrounding environment. However, coatings should not be con- sidered infallible. Handling and installation of the sheet piling can often lead to scratches, nicks and other localized damage. Imperfections and voids are also present during the coating process. These things can compromise an otherwise excellent coating system. This is where cathodic protection becomes an important second line of protection. Protecting the soil side The buried portion of sheet pile pre- sents a different challenge from the water exposed side. For the soil side, magnesium anodes can be an appropriate solu- tion. Magnesium provides a relatively high driving voltage, typically around
-1.55V, which allows it to provide use- ful current in soil environments. There is however a trade-off. Magnesium has relatively low effi- ciency — approximately 50 percent, compared with roughly 90 percent for zinc and aluminum. Consequently, magnesium can provide stronger driv- ing voltage but may consume more quickly for a given amount of useful output. Selecting the appropriate anode material requires careful consideration of the specific environment in which the anode will operate. When rehabilitation beats replacement At Cadet Point Marina, the existing sheet pile had already suffered signifi- cant deterioration. At this point, simply installing a new cathodic protection system was not an option. The existing structure required rehabilitation. Replacing the sheet pile altogether would have been extremely expensive and impractical. Permitting require- ments presented one challenge, while limited access made bringing the
equipment necessary for replacement particularly difficult. The project team chose to rehabili- tate the existing seawall. A fiber-reinforced polymer (FRP) jacket-type system with galvanic anodes, was selected to address the severely deteriorated steel in the tidal and splash zones. This approach allowed the existing structure to remain in place while providing a new protective barrier in one of the most aggressive portions of exposure. One structure — multiple electrolytes This cathodic protection design introduced another important con- sideration: galvanic anodes can oper- ate using different electrolytes. In this case, seawater, concrete, and soil. However, these electrolytes have vary- ing resistivity. Concrete is far less effi- cient as an electrolyte compared to seawater. Consequently, the anodes in concrete need to be installed much closer together than the bulk alum- inum anodes placed in the water to provide the required protection. This project also demonstrates how installation considerations can influ- ence design. The larger bulk aluminum anodes were designed to be connected to the steel above the water line, reducing the amount of underwater work required during installation. For mar- ine rehabilitation projects, this can be a significant advantage. Every addi- tional task performed underwater can increase dive time, equipment require- ments, complexity and cost. Designing the anode system to minimize under- water installation can improve both project efficiency and worker safety.
The full design of a sheet pile wall.
October 2026 — PACIFIC PORTS — 33
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