Recognized for conquering the Oregon Inlet’s treacherous current, constantly shifting bathymetry and violent storms, the HDR-designed Marc Basnight Bridge in North Carolina was recently honored with the Deep Foundation Institute’s Outstanding Project Award. The award recognizes the innovative foundation design of the $252 million bridge and will be given at DFI’s awards banquet on Oct. 17 in Chicago.
The new 2.8-mile bridge provides a 100-year service life, resists unprecedented scour depths and minimizes environmental impacts while offering a reliable, safe passageway for residents, visitors and tourists. As the lead design firm, HDR provided all roadway, geotechnical and bridge design as well as environmental permitting services for the new bridge.
The structure provides a critical link across the Oregon Inlet, which is widely acknowledged as the most dangerous channel on the Atlantic Coast. Its predecessor, the Herbert C. Bonner Bridge, suffered from severe scour and deterioration in the harsh marine environment, resulting in nearly continual maintenance, repair and retrofitting by the North Carolina Department of Transportation.
“For many years, the potential scour design challenges have been known,” says geotechnical engineer Brian Keaney. “However, through a lot of hard work and our understanding of the subsurface conditions, our geotechnical team pioneered innovative pile verification methods that NCDOT and the design-builder accepted to solve this unique problem.” HDR
An innovative bridge foundation design that used a combination of jetting and driving to install precast, pre-stressed concrete piles was key to the project's success. The foundations were designed to resist scour depths as great as 84 feet. Installing piles to the needed depths meant developing a first-of-its-kind method for calculating scour loss.
“Throughout this project, I’ve told people that the replacement of the Bonner Bridge isn’t a bridge job; it’s a complex marine foundation job with a bridge stuck on top,” says Domenic Coletti, design manager for the project. “The foundations were the key to the entire project.”
To maximize efficiency, the bridge was divided into five regions, with the design of each region’s foundations tailored to fit its distinctive subsurface and scour conditions, span length and height requirements, and load demands. In total, there are 690 piles measuring more than 15 miles in length combined.
The new bridge opened to traffic on Feb. 25, 2019, and provides a modern link between Bodie and Hatteras Islands. It will improve access to jobs, healthcare, education and recreation for the community, benefit local tourism and help feed a robust economy.