NCDOT listens to the ground as it rebuilds I-40 in the Pigeon River Gorge
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- NCDOT installed 123 monitors to track ground movement along damaged I-40.
- Sensors alert engineers in real time to shifts that could threaten the highway.
- Rebuilding effort includes a causeway and bridge to haul stone from a new quarry.
Interstate 40 was closed for months after more than a mile of the eastbound lanes fell into the flooding Pigeon River after the remnants of Hurricane Helene hit Western North Carolina.
Now, as the N.C. Department of Transportation works to rebuild I-40, it has installed electronic monitors to let it know if the ground along the highway begins to shift.
The monitors will alert contractors to any movements that might affect their work and provide an early warning if the construction zone or the surviving westbound lanes are in danger of collapsing.
“They provide information regarding any sort of movement of the slopes,” said Josh Deyton, NCDOT’s regional construction engineer. “Essentially it provides 24/7 monitoring.”
I-40 was built on a shelf blasted into a side of the mountains through the Pigeon River Gorge. For most of its history, the main threat to the road were rocks and boulders falling onto the pavement from above.
But the historic flooding after Helene last fall ate into the rock face supporting the highway, taking guardrails, shoulders and eastbound travel lanes in several places in North Carolina and Tennessee.
Highway departments in both states worked to partially reopen the highway in February by creating two-way traffic on the surviving westbound lanes. Altogether, there’s about 9 miles of two-way traffic on either side of the state line, through a zone where contractors are moving rock to re-establish the roadbed for the eastbound lanes.
NCDOT installed about 123 ground monitors over a four-mile stretch of highway, concentrated in areas where the river did the most damage. Drivers might see them mounted on the concrete median barrier between the east and westbound lanes or along the eastbound shoulder or the edge of embankment.
There are three basic types:
- Ground-mounted sensors tied to a global navigation satellite system that monitor settlement and lateral movement near the surface
- Tiltmeters that monitor the slant or slope of the existing embankment and any movement
- Shape arrays installed deep under the embankment that monitor subsurface movements within the embankment in relation to the bedrock underneath
All three types of monitors send data to a website, with alerts if something is amiss, according to NCDOT spokesman David Uchiyama.
“This is done in real-time so our engineering team can get an immediate notification if movement is happening outside of the parameters,” Uchiyama wrote in an email.
The Tennessee Department of Transportation does not have a similar set of monitors in the gorge. Spokesman Mark Nagi said TDOT is testing the technology statewide and has one monitor in East Tennessee along a fence designed to catch falling rocks.
NCDOT expects it will take three years to rebuild the eastbound lanes of I-40 through the gorge. Contractors have nearly finished constructing a four-mile causeway along the river that will be used to truck stone and other materials to the base of the cliff.
The next big step will be installation of a temporary bridge across the river that will be used to truck stone from a new quarry in Pisgah National Forest. The stone will be used to gradually build up the roadbed to support the highway.
This story was originally published July 19, 2025 at 7:00 AM with the headline "NCDOT listens to the ground as it rebuilds I-40 in the Pigeon River Gorge."
