The winner of the 2019 DFI Outstanding Project Award (OPA) is the team of HDR (engineer), PCL Civil Constructors (general and foundation contractor) and North Carolina Department of Transportation (owner) for the innovative foundation design of the 2.8-mile-long Marc Basnight Bridge in North Carolina’s Outer Banks. The award will be presented at the DFI 44th annual conference on deep foundations in Chicago, Oct. 15-18, 2019.
The new bridge replaces the Herbert C. Bonner Bridge and was built using first-of-their-kind design and construction methods to provide a 100-year service life, resist unprecedented scour depths and minimize environmental impacts while offering a reliable, safe passageway to and from Hatteras Island.
Capable of resisting wind, wave and vessel collision forces from the worst storms in the Atlantic Ocean, all while subject to unprecedented scour depths, the new bridge is subject to 12 feet/second (8 mph) currents, winds up to 105 mph and vessel impacts up to 2,151 kips. Its foundations were designed to resist scour as deep as 84 feet below sea level.
The bridge foundation design was key to project success, but also posed the greatest challenges. Driven, prestressed concrete piles were selected for the long spans as well as the approach and transition spans, and provided the required strength and durability. To address the concern of how to drive large displacement piles through dense sand, the team developed innovative jetting installation methods. The need to optimize the design led to the extensive use of refined soil-structure interaction analyses.
The approach spans, with significantly less scour and ship impact loads, are supported by highly-efficient foundations with three or four 54-inch diameter vertical concrete cylinder piles. The transition spans and the high level, long navigational spans use a combination of cast-in-place reinforced concrete pile caps with six to thirty, 36-inch-square concrete piles in a battered configuration to provide greater lateral resistance against wind and ship impact loads under deeper scour conditions. In total, there are 690 piles measuring more than 15 miles in total length of piles installed.
The OPA was established in 1997 to recognize the superior work of DFI members. The projects are selected by a committee based on size, scope and challenges faced; degree of innovation and ingenuity exercised; and the uniqueness of the solution to the difficulties of the job.
The DFI is an international association of contractors, engineers, academics and suppliers in the deep foundations industry with more than 3,500 members worldwide. For more information about the Deep Foundations Institute, visit www.dfi.org.