Farragut Field and Santee Basin East Bulkhead Construction at the United States Naval Academy

Abstract: The Farragut Field Bulkhead defines the northern and northeastern edge of Farragut Field at the United States Naval Academy. It also serves as a temporary mooring location for training vessels used by the Academy. The Santee Basin East Bulkhead defines the eastern edge of the Santee Basin and provides a mooring location for small vessels and access to multiple finger piers and floating docks. Severe corrosion and widespread deterioration along both facilities led to sinkholes developing along the bulkheads. Due to the extent of the deterioration, it was concluded that rehabilitation of the bulkheads would be impractical, cost-prohibitive, and non-compliant with UFC design criteria. Therefore, an approximately 1,400 ft long replacement bulkhead was designed. The replacement design was completed in 2022 and construction was completed in 2024.

Site investigations performed during the design indicated that the deadman system was in a serviceable condition and could likely be utilized as part of the replacement project. However, the deadman system along Farragut Field did not meet the structural requirements for the new bulkhead. Conversely, the existing deadman system along the east wall of Santee Basin was sufficient to support the replacement bulkhead along that portion of the project. Therefore, two anchorage methods were utilized: The bulkhead along the eastern side of Santee Basin would reutilize the existing deadman system while the bulkhead along Farragut Field would receive a new deadman.

A test pile program was developed to verify the pile lengths developed during design. There are two types of piles utilized in the deadman system along Farragut Field: steel H-pile clusters in the corners and square precast prestressed concrete piles driven in an A-frame pattern along the straight stretches of the Farragut Field Bulkhead. The length of the concrete piles was reduced following testing, reducing cost and increasing the rate at which the concrete piles could be installed.

The deadman system along Farragut Field utilizes nearly all batter piles. In order to increase the rate of pile installation, the contractor’s internal engineering team and field crews developed a pile driving frame that was both highly mobile and easy to align. The frame allowed for rapid connection with the pile hammer and was utilized during the driving of both concrete and H-piles; increasing efficiency as pile driving crews did not have to alternate between frames when moving between tasks.

Part of the pile cap for the replacement bulkhead extends below the waterline. To address this challenge, the contractor developed a cantilever formwork system that extended out and hung down to the bottom of the new pile cap but did not require the use of in-water supports. This reduced the amount of channel bottom disturbance caused by construction activities while allowing for more efficient setup and takedown compared to systems that would utilize in-water supports.

This project provides a case study on innovative design with regards to reuse vs bypassing of existing components; innovative construction method development; and efficient communication between contractors, engineers, and owner.

How does this project / topic contribute to the advancement of the industry and profession?: The project involved both the reuse of the existing deadman anchorage system for part of the project and a new deadman system for the remainder. This combination of approaches allowed for a more economical end product by only bypassing the systems that could not be reused while utilizing systems with significant service life remaining.

The cantilever formwork and pile driving frame developed for the onsite challenges can be repurposed or modified to address similar challenges others may face on their projects.

In situ pile testing validated the pile lengths required, reducing foundation contingency costs and increasing efficiency.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: The cantilever formwork utilized for concrete cap placement is a unique and innovative system used where access and additional support is difficult. It allowed for the pile cap to be formed and placed without the need for in-water supports, which is beneficial for areas that are either in deep water, areas where in-water disturbances are restricted, or where waters are impaired.

The frame developed to support driving batter piles allowed for rapid relocation and setup along with providing a platform that made precision pile installation achievable with minimal effort.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: One of this project’s challenges was the undersea high voltage electrical cable that runs along the perimeter of Farragut Field. This cable was located within the anticipated footprint of the new sheet pile bulkhead. The cable required relocation without disconnecting the cable from one end or the other so as to not be cut in half by the new sheet pile bulkhead.

Additionally, there was limited laydown/working area within the project site. This led to a combination of utilizing multiple floating plants and utilizing barges for additional laydown areas to supplement land-based construction operations.

Who is the target audience for this paper?: The target audience for this paper will be facility managers, consulting engineers, and construction professionals. This project showcases innovative construction means and methods along with decisions made during design to efficiently and effectively address unique challenges.