[waves crashing] - [Narrator] How do you reattach part of a major four-lane highway to the side of a mountain?

- When hurricanes Helene slammed into Western North Carolina, September 27th.

Some rivers crusted as high as 30 feet, damaging a few thousand bridges and roads, and in many cases changed the landscape as the water's power reshaped the riverbanks.

The water swelled here at the Pigeon River Gorge, took out a giant chunk of the eastbound lanes of Highway 40 at the Tennessee border, severing a vital transport link to the eastern seaboard.

- - [Reporter] Have you ever seen anything like this before?

- In my 13 year career, I've never seen damage on this scale or this significant.

- [Narrator] So, what to do?

The North Carolina Department of Transportation invited a small group of journalists to take a look at the plans underway to fix it.

Highway 40 was damaged in about nine places along a four mile stretch here at the Pigeon River Gorge, and no area was as damaged as the one we visited.

Engineers say they'll manage a temporary fix with a two lane road, but that bottleneck will be there for some time to come and impact the roughly 26,000 vehicles that travel through it every day, - We'll have one lane each direction.

The plan is to have one lane westbound, one lane eastbound, and to split them at the tunnels that are behind me.

- [Narrator] That's the plan, but Halene created new challenges.

- This is a completely different type of failure for this corridor of roadway.

A fill slope failure this long and this extensive is not something that we've ever seen before.

- [Narrator] So how does it work and what are they gonna do?

There's no one-size-fits-all solution to every bridge or road here in the mountains, but there is a thing they do.

It's called soil nailing.

- [Nathan] So a soil nail is a steel nail anchored product.

What we do is we look at a specific slope failure and we design to pin that slope back.

Several nails are installed in those locations.

They're installed on a specific angle and a specific spacing so that we can make sure that the type of material that we're trying to pin is completely pinned back into competent rock.

- Tanner says once those nails are installed, they drape wire tape over the area and spray concrete, or what's called shotcrete, across the surface to bring it together.

The emergency repairs here at the gorge will be in the neighborhood of $10 million.

The more permanent repairs for the region as a whole are estimated to easily pass 50 billion.

- An event of this scale is historic for a lot of the people that work in DOT and this is our home and we wanna do a good job and get these roads repaired as quickly and as efficiently as possible 'cause we're here to serve the people of North Carolina.