Abstract:
The first 5-miles of Interstate 40 (I-40) in western North Carolina within the Pigeon River Gorge suffered significant scour during Hurricane Helene in late 2024. The severity of the damage across the corridor varied based on river hydraulics in this section of the gorge and included loss of embankment, roadway, and in some cases, failure of existing pile and lagging retaining walls and scour countermeasures installed for previous slide repairs. The repair of I-40 has been progressing under a CMGC procurement method to allow for collaboration between the design team and construction team to develop constructable solutions in the challenging terrain with limited access to the river. To meet resiliency goals for the repair established by the project team to endure another 500-year storm event, the repair solutions were divided into two systems (1) approximately 3.5 miles of roller-compacted concrete (RCC) buttress with toe protection for scour countermeasures, and (2) approximately 1.5 miles of drilled-in interlocking pipe pile (IPP) walls with post-tensioned tieback anchors. Use of RCC lends itself to linear sections of the alignment, comprising of no-slump concrete placed in 12-inch compacted lifts using conventional earthwork equipment. Cured RCC provides a durable surface for high-velocity flow environments similar to the more common application in hydraulic structures. The IPP system consists of permanent steel casing, a sacrificial ring bit, welded-on steel interlocks, and a full-face down-the-hole hammer (DTH) drilling system. By coupling the use of DTH drilling methods with a sacrificial ring bit, the system provides a continuously cased hole with an annulus large enough to embed interlocks into rock. At the time of this presentation the full design documents are submitted and construction is underway. This presentation will provide an overview of the design approach used on this mega-scale transportation project. An overview of the IPP wall and RCC buttress retaining structures will be provided.
Key Terms: Anchored Earth Retention, Slope Stabilization, Roller-Compacted Concrete, Interlocking Pipe Pile