DFI Announces 2019 Outstanding Project Award winners

The winner of the 2019 Deep Foundations Institute (DFI) Outstanding Project Award 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 (4.5km) long Marc Basnight Bridge in the Outer Banks, North Carolina, USA.

 The Marc Basnight Bridge in North Carolina, has won the 2019 DFI Outstanding Project Award

The Marc Basnight Bridge in North Carolina, has won the 2019 DFI Outstanding Project Award

The award will be presented at the DFI 44th Annual Conference on Deep Foundations in Chicago, in October.

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 minimise 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 12ft/s (8mph or 13kph) currents, winds up to 105mph (170kph) and vessel impacts up to 2,151kips (9.6MN). The foundations for the new bridge were designed to resist scour as deep as 84ft (25.6m) 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 optimise 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 54in (1,372mm) 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 30, 36in (914mm) 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 (24.1km) in total length of piles installed.