The expected completion of a bridge on the Denali Park Road has been pushed back from 2025 to 2026. The 90-mile road into Denali National Park remains closed at about the halfway point, where it crosses a melt-driven landslide that has obliterated the road.
Denali National Park public affairs officer Sharon Stiteler says the new timeline is primarily the result of a geotechnical issue.
“The discovery of more clay than was anticipated on the west side of the project,” she said. “Originally it looked like it was going to be 30,000 cubic yards of clay that was going to be excavated, and now it looks like it’s going to be 80,000 cubic yards, and that’s a significant change.”
The 475-foot bridge — expected to cost $100 million — will span a melting rock glacier in Polychrome Pass that crosses the gravel road at mile 45. The road closed in 2021, after the landslide began moving too fast for maintenance crews to keep up.
“It got to the point of calculating how far they had to go to pick up the gravel, how much it was going to take to get out here to be able to maintain the road and make it safe enough for drivers to go across,” Stiteler said.
Park science and resources team leader Dave Schirokauer underscores the challenging alpine terrain the section of the Park Road traverses, and how it’s changed since the road was built.
“They probably had no idea they were building a road across a rock glacier,” he said. “It was completely inactive back then and it wasn’t really a problem until 2016, and so 1930 until 2016, it was a great road and just a little bit of climate warming that’s occurred in that era, along with the disturbance of creating a cut through here, really woke up this rock glacier.”
Park engineer and bridge project manager Steve Mandt underscored the scope of the bridge project.
“Just a massive amount of engineering and detail and thought goes into this,” he said.
Mandt says the plan that calls for incrementally building the truss-style bridge across the slide without any underlying support.
“Starting at both the east and the west and then progressively work toward the center, so they will at some point be assembling bridge kind of out in space kind of hanging over the valley below,” he said.
Heat dissipating thermosiphons will protect ice beneath the rock where the bridge’s abutments will be stand on either side of the slide.
Work on the bridge across was supposed to start in May, but that’s been pushed to July. Bridge contractor Granite Construction began mobilizing in the park this spring and is in the process of building a 50-worker camp in a gravel pit at mile 27 of the Park Road.