Cumberland Gap Parkway Tunnel Project

Federal Highway Administration and National Park Service

Cumberland Gap, KY, 1989

Evergreen Wall Plantable Retaining Wall System

Approximately 34,040 sf of specially colored retaining wall

Tunnel Wall during constThe steep road cuts required for the highway and tunnel project along the historic Cumberland Gap region between Kentucky and Tennessee used custom-colored Evergreen Walls to meet the DOT’s and FHWA’s structural soil-retention specifications as well as the aesthetic concerns of the U.S. National Park Service. The natural stone-colored walls offered the park service the strength of precast concrete; the cost advantages of standardized elements; sound and heat reduction; and aesthetic harmony with the natural environment. The need to purchase valuable land was minimized with engineered soil retention walls. Approximately 34,040 sf of specially colored retaining wall units were used on the project.   Wall heights of up to 20 vertical feet lined each side of the Kentucky side of the tunnel.  Up to 1,600 ft2 (150 m2) of wall was placed daily, allowing the project to be completed ahead of schedule.  At Cumberland Gap, the design of the Evergreen Wall units allowed sufficient ingress of rainwater and sunlight to support lush vegetation. As the plants became established and cascaded over the precast unit, noise reduction increased. “The wall system offered us an excellent medium in which to grow large plants to blend into the environment,” said Robert Leary, the U.S. Federal Highway Administration engineer on the project.