Granite Construction won a $100 million project to build a single-span steel truss bridge over an actively moving landslide in Alaska’s Denali National Park, according to a company press release.
The Pretty Rocks Landslide intersects Denali Park Road near its midpoint at Mile 45.4. While the landside has been active since at least the 1960s, in recent years its movement has accelerated, and for the past two tourist seasons, it has rendered the remaining 47 miles of roadway through the park impassable.
According to the National Park Service, before 2014, the landslide only caused small cracks in the road surface and required moderate maintenance every 2–3 years. But the rate of road movement within the landslide evolved from inches per year prior to 2014, to inches per month in 2017, inches per week in 2018, inches per day in 2019, and up to 0.65 inches per hour in 2021. Now, the landslide is moving at a rate of up to 12 inches per day.
The Polychrome Area Improvements project calls for a 475-foot long bridge to span the area. A combination of earthwork, micropiles, rock anchors, precast concrete abutment and thermosiphons — which maintain permafrost in a frozen state — will support the bridge.
"Our specialized team is enthusiastic to partner with FHWA and its designer to produce a constructible design," said Todd Keller, Granite project executive, in the release. "Minimizing our impact on park operations and preserving the natural beauty of the site is of utmost priority while constructing this challenging project.”
Preconstruction started in January 2023 and will be complete in five months. Construction work is expected to begin in the spring of 2023 and to be completed by May 2025.
