Resilient Wharf Extension Enhances Container-on-Barge Operations in Charleston’s Largest Terminal

Abstract: The South Carolina Ports Authority (SCPA) is executing the Inner-Harbor Container Barge Operation project to enable marine transfer of containers by tug and barge from the Wando Welch Terminal (WWT) to the Hugh K. Leatherman Terminal (HLT), then on to the future rail-served Navy Base Intermodal Facility (NBIF) located in North Charleston, SC. The primary tenets of this project are to mitigate safety and environmental impacts of the growing ground transportation network through alternative transport methods. A critical component of the project is extending the existing 3,800-foot-long (WWT) container wharf by 700 linear feet to service up to two container barges while maintaining its capacity to simultaneously service three neo-Panamax container ships. This paper describes the design solutions adopted to provide a seismically resilient structure that not only allows a seamless operational transition between existing and new infrastructure but also minimizes maintenance required for the structure, dredging, slope protection, and utilities, all the while servicing a variety of vessel types.

The berth extension structure is designed with an underwater slope engineered to address construction, operational, and seismic stability considerations. This includes providing a bench and riprap offset away from the berth pocket to reduce the risk of armor stone impacts on future maintenance dredging. To reduce construction costs, a two-step live load criterion was used for the structure and the geotechnical design of piles. The berth is founded on high-capacity, driven precast prestressed octagonal concrete piles with steel H-pile stingers that penetrate the unique Cooper Marl (stiff clay) subsurface formation. The serviceability-based superstructure design is comprised of cast-in-place deck topping and pretensioned deck planks supported on high-capacity concrete transverse and longitudinal/crane beams. A unique deck detailing connection allows functionally compatible STS crane rail operations across the interface between the new berth extension and the existing stiffer wharf segments which lack in seismic detailing. On-site stormwater treatment is provided using precast vaults integrated with the deck structure and eliminates the need for costly retention structures or tying into the existing fully built out terminal stormwater network. Construction of the berth extension is expected to commence in 2025 with operations beginning in 2027.

How does this project / topic contribute to the advancement of the industry and profession?: The project sets an example for design engineers assisting port owners in their effort to diversify their operations and services by expanding existing infrastructure in seismic regions with unique soil conditions.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: The project implements modern analysis and design techniques and innovative features such as on-site stormwater treatment with minimum maintenance costs and an under-wharf soil profile with a bench and riprap offset away from the berth pocket to facilitate future maintenance dredging.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The most challenging aspects of the project included designing the wharf extension structure, its connections to the existing wharf structure and container yard bulkhead, and the soil profile underneath it with due consideration of seismic demands, all while minimizing future maintenance efforts.

Who is the target audience for this paper?: Target audience includes container terminal owners and operators, port designers, and marine contractors.