Portsmouth Marine Terminal Offshore Wind Staging Port Planning and Design

Abstract: Dominion Energy leased Portsmouth Marine Terminal (PMT) from the Virginia Port Authority in 2021 to serve as a staging port in support of the Coastal Virginia Offshore Wind (CVOW) project. PMT was previously designed and utilized for container cargo operations, serving as a key container port for the Port of Virginia for more than five decades. To accommodate the CVOW project, new wharf structure, backlands, and berthing space were required to accommodate the revised operations. This required a complete closure and renovation of the over 50-year-old port and rapid coordination between Dominion, the Port of Virginia, and the design team to get the project completed on the CVOW project timeline.
The offshore wind (OSW) cargo anticipated to move through PMT includes wind turbine generator (WTG) blades, towers, and nacelles, as well as foundation elements including transition pieces (TPs) and monopiles (MPs). In addition, other CVOW related cargo including offshore substations, jackets, pin piles, pile templates, and pile hammers are all anticipated to be delivered and stored at PMT. These items require different structural loadings, spaces, as well as different equipment to move and even power to store. This paper will address how the planning and design was completed to accommodate the 500-ton TPs, 800-ton nacelles, 1,500-ton MPs, and 4,000-ton topside structures.
All of these challenges also had to be designed and constructed quickly, with the first cargo arriving approximately three years after the lease was signed.
To accommodate these challenges, the existing 750 psf wharf had to be replaced with a 2,050 psf roll-on roll-off (ro-ro) wharf and two 5,100 psf wharves to accommodate the crane load for the TPs, as well as upright towers and nacelles. With bedrock not close enough for piles to reach, friction piles were required, with 36-inch square concrete piles selected on a 10-foot by 15-foot grid to support these significant loads. The three wharves required were staged in the construction documents to ensure the first MPs delivered in 2023 had the ro-ro wharf and associated backlands completed for Milestone #1, with the delivery wharf completed for Milestone #2 in time for the TPs to arrive in the spring of 2024.
The backlands were designed with a stiff upper pavement layer comprised of two layers of geogrid and more than 2 feet of stone on top of the previous pavement base layer to support heavy cargos. Rigid inclusions were utilized in key areas to support known storage areas of the nacelles and upright towers, with approximately 8 acres of the more than 60 acres of backlands targeted with the rigid inclusions.
While this project is still under construction, with two of the three milestones currently completed and the third milestone set for completion in January 2025, the intent is to cover the lessons learned for the first OSW staging port in the U.S. handling foundation elements and WTG elements simultaneously, with key considerations for how other ports can tackle these challenges as the U.S. OSW industry expands.

How does this project / topic contribute to the advancement of the industry and profession?: Port planning relating to offshore wind is still in its early stages, with even the exact requirements not fully detailed. This will detail both the planning aspects as well as design-related aspects including the needed bearing capacities, acceptable settlement, and uniform live loads.
Even though Europe is about 15 years ahead of the U.S. in the offshore wind industry, their ports are not as advanced, with lower loading capacities than those of the U.S. staging ports being constructed, so this topic does advance the industry both in the U.S. and Europe.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: The PMT project implemented unique solutions to the heavy bearing capacities required for the OSW components, designing a dense graded aggregate pavement section that could accommodate the loads, with the rigid inclusions targeted for key areas to reduce settlement. In addition, 36-inch-square concrete piles were utilized, which although are not a “new” technology, are certainly not common for port infrastructure and caused additional challenges during construction due to heave and lateral movement of the piles.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The most challenging aspect was the tight timeline to complete the project. The first components arrived approximately three years after the lease was signed. The design had to be scoped, completed, project bid, existing wharf demolished, and the first wharf completed in that timeline. Also, with Federal grant money attached to the project, NEPA assessments were required before construction could begin, which required tight coordination between the design and permitting team of VPA. This was addressed by having close coordination with Dominion and the VPA, as well as with the contractor to quickly resolve issues encountered in the field.

Who is the target audience for this paper?: The target audience is port authorities looking to support offshore wind as a staging port, and engineers looking to plan and design staging ports.