Subsurface Exploration for I-40 Reconstruction in the Pigeon River Gorge Post Hurricane Helene-Paper

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Hurricane Helene’s September 2024 flooding caused widespread damage to Interstate 40 in North Carolina’s Pigeon River Gorge, where high-velocity flows undermined embankments along the river. To support emergency reconstruction, Schnabel Engineering and the RK&K design team carried out an expedited, three-phase subsurface exploration program.<br /><br />The investigation combined historical records, observations of temporary soil-nail drilling, air-track rock probes, conventional rock coring, optical televiewer logging, multichannel analysis of surface waves (MASW), and laboratory testing. Teams collected data across and along the corridor, coordinating with NCDOT and the construction contractor while temporary stabilization work and reconstruction activities were underway. The program included 473 soil-nail logs, 308 air-track probes, 166 coring locations, approximately 15 miles of MASW surveys, and about 300 laboratory tests.<br /><br />Results showed highly variable depths to bedrock and a thick, coarse “shot rock” embankment containing large boulders. Bedrock formations were layered and dipped steeply toward the river, creating potential stability concerns. Rock-core strengths varied by formation, and testing found no evidence of acid-producing rock.<br /><br />To organize the large, rapidly changing dataset, the team used Mortar, an interactive mapping platform that integrated field logs, historical information, laboratory results, geophysical data, and other sources. Near-real-time visualization helped stakeholders coordinate fieldwork, review conditions, and make design decisions sooner.<br /><br />The findings informed two selected repair approaches: roller-compacted-concrete embankment buttressing and continuous pile walls. The project demonstrates how coordinated exploration and integrated data management can accelerate design for complex emergency infrastructure repairs.

Keywords

Hurricane Helene

Interstate 40

North Carolina

Pigeon River Gorge

subsurface exploration

embankment stability

rock coring

MASW surveys

Mortar platform

emergency reconstruction