Channeling a New Era on the Outer Banks
The Marc Basnight Bridge is designed to provide a 100-year service life, addressing the many problems of its predecessor
By Sophia Acevedo
Sprawling for miles across the Oregon Inlet and providing a link between Bodie Island and Hatteras Island, The Marc Basnight Bridge, which carries the North Carolina 12 Highway, serves as an impressive feat. Not only is it a visually superior replacement to the Herbert C. Bonner Bridge, but it serves as a key hurricane evacuation route for the state.
The need for a new bridge became evident as the previous bridge — the Herbert C. Bonner Bridge — neared the end of its useful life.” Domenic Coletti, senior bridge engineer at HDR Inc. and principal bridge engineer
The Marc Basnight Bridge has received a number of accolades including: ASCE North Carolina Project of the Year, ASCE Outstanding Civil Engineering Awards Honor Award, ASBI Award of Excellence, PCI Sustainable Design Award as well as several others. Now, it can tack on one more award as it is the winner of our American Infrastructure’s Bridge of the Year.
Work on the replacement bridge began decades before its construction began through careful study from the North Carolina Department of Transportation (NCDOT).
The NCDOT had to frequently manage and repair the old bridge, since the harsh marine environment of the Oregon Inlet caused significant scour and deterioration. Furthermore, the Army Corps of Engineers had to dredge the channel constantly throughout the year to provide access for ships to pass since there was only a single 13-foot span to provide ship passage.
Facing these significant challenges, in 2011 a design-build team that consisted of PCL Civil Constructors and HDR Inc. was selected to design and build a replacement bridge.
“The need for a new bridge became evident as the previous bridge — the Herbert C. Bonner Bridge — neared the end of its useful life,” Senior Bridge Engineer at HDR Inc. and Principal Bridge Engineer Domenic Coletti said.
Groundbreaking for the project began in 2016 after litigation delayed the project for three years, but overall, the 2.8 mile bridge was completed on schedule and cost $254 million.
Overcoming a Harsh Environment
Once beginning construction on the project, the environment proved to be one of the first issues that the design-build team needed to tackle.
For instance, despite dealing with loose sands and changing bathymetry, the engineering team figured out a solution that minimized future dredging by making multiple ship passages and also taking account of the environment’s natural movement.
“As the inlet’s natural channel shifts, lighting and the markings on the bridge can be adjusted to redirect ships to the proper span, minimizing the need for dredging,” says Coletti.
The engineering team also designed and built pile bridge foundations that were up to 84 feet deep to accommodate the loose sand and swift currents. According to Coletti and the HDR team’s knowledge, no one has previously designed and built such a foundation. By creating hindcast simulations of more than 180 storms dating back 160 years, the team was able to develop scour profiles. This, in addition to testing soil-structure interaction through FM-MultiPier modeling, allowed for design optimization and greater confidence for NCDOT that the bridge would be able to deal with the worst cases of scour and loading.
Another environmental condition that posed a formidable challenge was the harsh saltwater. Since there wasn’t much space available at the site to hold storage, materials had to be brought over long distances. The team addressed this by primarily using repetitive details and precast concrete parts, simplifying the construction process and minimizing the work needed to be done near the saltwater environment.
“Fabricating these pieces offsite promoted a quality and durability that would have been difficult to achieve in the harsh marine environment, while also improving the reliability of material delivery and increasing the speed and simplicity of construction in the field,” says Colleti.
Preserving Wild Animal and Plant Life
With the Pea Island National Wildlife Refuge, Cape Hatteras National Seashore, 20 state- or federally-listed protected species, and a designated submerged aquatic vegetation habitat located nearby the project, extensive measures of precaution needed to be taken to minimally impact the local animal and plant life.
To address this, the team used the minimum number of vertically driven piles in the bridge’s north approach spans, near where the Cape Hatteras National Seashore was located. They also used lights during nighttime construction that minimize light pollution and its impact on turtle life.
“Perhaps most significantly, a “leap-frog” construction approach limited the length of the work trestle in the sensitive SAV areas as construction of the new bridge progressed from north to south, spans from the north (trailing) end of the work trestle were moved to the south (leading) end,” says Colletti. “This minimized temporary environmental impacts, particularly shading of the seagrass beds.”
Pride Among Outer Banks
Outer Banks residents were actively engaged and excited even before construction of the project began. A local citizen
group, “Bridge Moms,” was created by a group of Hatteras Island mothers who wanted to show support for the replacement bridge so that their children could have safe and reliable access to medical and educational facilities that were located north of the Oregon Inlet.
After the project was completed in 2019, NCDOT and Dare County hosted a “Community Day” in February to commemorate the opening of the new bridge. Local politicians, NCDOT and the prideful “Bridge Moms” also served as speakers of the event, as people strolled or biked through the open bridge. Though having to endure 30-degree temperature and cold winds, over 2,000 local residents joined in the celebration through a blessing and wreath-laying ceremony.
Sophia Acevedo is the assistant editor at American Infrastructure Magazine. She can be reached at email@example.com.