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January 22, 2018
Project: Abraham Lincoln Bridge
Client: Kentucky Transportation Cabinet, Jacobs Engineering Group
Varying geotechnical conditions at each end of this cable-stayed bridge brought unique challenges to the COWI team, which designed its foundation system.
The new six-lane, three-tower bridge is 2,100 feet long and spans the Ohio River between Louisville, Kentucky, and Jefferson, Indiana.
The successful completion of the span was the result of a collaborative effort among the owner, Kentucky Transportation Cabinet; Walsh Construction, the design-build contractor; Jacobs Engineering Group, the prime consultant; and COWI North America, the engineer of record.
The subsurface conditions at the site included highly variable depths to bedrock at each end of the bridge. This resulted in a stiffness contrast for the structure that required careful consideration of foundation axial capacity and lateral stiffness in order for the bridge to remain technically and economically feasible.
Drilled shafts support the bridge's three main towers and the two anchor piers. Each tower is supported by a single row of four, 12-foot-diameter drilled shafts socketed into limestone.
Use of this foundation system reduced the foundation installation time, accelerated the overall bridge construction schedule and resulted in a very flexible system. Additionally, it minimizes the dimension perpendicular to the river flow and maximizes the main span navigation clearances. As a result, environmental concerns are addressed by minimizing disturbance to river flow and the risk of debris accumulation.
The design method didn't come without its challenges, however. The single-row approach (the Abraham Lincoln Bridge was the first major cable-supported bridge where a single line of large-diameter drilled shafts was used for each tower foundation) resulted in high geotechnical and structural demands on the drilled shaft foundations, both under critical unbalanced loads during the erection of the superstructure and under governing live and wind loads.
Variable limestone depths on both the Kentucky and Indiana sides created severe foundation stiffness contrasts that affected the load transfer from the superstructure to the substructure and the location of the bearing fixity. The design team pushed the boundaries to address these technical challenges throughout the duration of the project.
The Abraham Lincoln Bridge is one of the first major bridges in North America on which a rational durability study was explicitly performed and incorporated into the design process. COWI engineers applied a “ruthless approach” to make every aspect of the project durable.
The bridge is designed to withstand a significant terrorist threat and cable loss and has high fracture toughness and a 100-year service life design. It can handle significant ship collision, incorporates substantial blast protection and features significant redundancy.
The foundation system played a critical role in the speedy completion of this project, which was finished four months ahead of schedule.