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 mi (4.5 km) long Marc Basnight Bridge in the Outer Banks, North Carolina. The award is being presented at the DFI 44th Annual Conference on Deep Foundations in Chicago, October 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.
The bridge is 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 ft/s (8 mph or 13 kmh) currents, winds up to 105 mph (170 kmh) and vessel impacts up to 2,151 kips (9.6 MN). The foundations for the new bridge were designed to resist scour as deep as 84 ft (25.6 m) 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 in (1,372 mm) 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 in (914 mm) 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 mi (24.1 km) in total length of piles installed.
The OPA was established in 1997 to recognize the superior work of DFI members. The project are selected by a committee based on size, scope and challenges of the project; degree of innovation and ingenuity exercised; and the uniqueness of the solution to the difficulties of the job.
