 |
| 1:53 video An unstoppable force: The Pretty Rocks Landslide There are over one hundred and forty landslides along the Denali Park road, the 92 mile road through Denali National Park and Preserve. None are more threatening than the Pretty Rocks Landslide at Polychrome Pass. Roughly 45 miles into the park, Polychrome Pass is steep, windy, and breathtaking with sweeping views of valleys and mountains. The landslide is moving the road at a pace of 12 feet per year. Geologists and park officials are constantly working to address the problem to allow bus travel, but the landslide may force a more permanent reroute in the near future. |
 |
| Alaska Magazine posted After nearly two weeks of inch-by-inch progress, the Pretty Rocks Bridge has reached its abutment at Denali National Park and Preserve. The park road has been closed beyond Mile 43 due to the creeping landslide but is on schedule to reopen in 2027 photo: NPS Denali Education Center Denali Park Village Maria Pietsch: I was in Denali in 2021 when they closed the road. We had reservations at the Road House which were canceled and we stayed outside the park. [A lot of sources said the park's access road was closed, but this is when I finally saw the date of 2021.] Emmet Williams: I’ve been working on this bridge, and it really is a feat of engineering. A very complicated launch system that has never been done before. The main truss is all the way across, and we are working on jacking down to its final resting place. [Aug 31, 2025] |
This is an earlier photo. After the bridge truss is built, they will build the launching truss inside it. They will then shove the launching truss across the gap to set down on the receiving tower.
"And then it will be disassembled as the permanent truss structure is launched and then jacked down to its final position....The bridge will be placed approximately 40 feet above the landslide area, so even though that area will continue to slide, it will not affect the bridge or those using it." [AlaskaContractor]
 |
| Carsten J. Gardner commented on the above post look close and you’ll see the crane! |
 |
| Digitally Zoomed |
 |
| Tyler LaBruyere commented on the above post 😎Cool😎 |
This satellite image is old because the hill side to the east of the former bridge is still intact. The new bridge will replace the small bridge and the curved road.
 |
| Satellite |
Park Road is built on a rock glacier here. As long as it was frozen solid, there was no problem. But climate warming has caused the glacier to melt and the road to move. "By 2016 the movement had increased further, a slump had developed in the road, and a monitoring program was begun. 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." [nps_nature]
 |
| nps_nature, NPS photo NPS road maintenance staff made an extraordinary effort in Spring 2021 to repair the road at Pretty Rocks. By August 2021, these road maintenance efforts were no longer sustainable in the face of the landslide’s accelerated movement. |
 |
| nps_nature, NPS photo This is what it looked like in Summer 2022. The personnel on the road are doing geotechnical investigations for the west abutment. |
Another view from the Summer of 2022. This is looking West.
 |
| nps_plan, NPS photo |
By 2023, the road is far down the side of the mountain. This is looking East.
 |
| nps_plan, NPS photo |
Another 2023 view.
 |
| AlaskaPublic, Dan Bross/KUAC Looking west across the Pretty Rocks landslide on May 5, 2023. |
This is an early rendering of the solution. Note the bus for scale. The truss is 25' (7.6m) tall.
 |
| nps_plan, Source: BGC and Jacobs Engineering |
The bridge is expected to cost $100m. The completion date was pushed from 2025 to 2026 because they expected to have to excavate 30,000 cubic yards of clay for the west side, but they discovered that 80,000 cu. yd. had to be removed. [AlaskaPublic]
The bridge is expected to be done in 2026, but the road won't open to the public until 2027 because other repairs need to be made in the western 45 miles of the road.
Designing the logistics to build in a wilderness was comparable to the complexity of the geotechnology work and the bridge construction itself. For example, they built a town to house the workers. Here we see the temporary road needed to access the bridge abatements. Every morning, they would inspect it and add gravel if needed. And some photos I've seen show that somehow they got a crane on the west side.
At least some of the equipment was moved to the west side using a helicopter. [nps_20250624]
 |
| AlaskaContractor, Fall 2024 "To mitigate the potential for permafrost thaw, twenty-three thermosyphons will be installed in the ground around the eastern abutment of the bridge. A retaining wall will also be installed on the uphill side of the road to the east of the bridge, as will a soil nail wall below the road near the east abutment, and rock dowels below the road near the west abutment for slope stabilization." This source puts the price tag on the project as $209m. |
Jun 24, 2025: they are done building the main truss and rollers have been added to the west end of the truss.
 |
| nps_20250624, Jacobs |
Jul 7, 2025: they have started building the launch truss inside the bridge truss while work continues on the receiving tower.
 |
| nps_20250708, FHWA |
Jul 15, 2025: just over half of the launch truss has been built. A bay is added at the opening of east end of the bridge truss, and then the launch truss is winched further into the bridge truss.
 |
| nps_20250715, FHWA |
Jul 30, 2025: the launch truss was finished, and they began launching it on Jul 25. By the end of July 26, it had reached the receiving tower and was secured in place. I wonder how big of a helicopter was needed to move that crane and front loader. I notice the road that we see in the above Fall 2024 AlaskaContractor photo has disappeared.
 |
| nps_20250730, proHNS |
This view from the river valley better shows how much material has already flowed down the mountain side.
 |
| nps_20250730, NPS Photo / K. Karnes |
Aug 5, 2025: The bridge has partially been moved across the gap. Because of limited space between the west abutment and the rocky cliffs, bays of the launch truss are removed as they clear the receiving tower.
 |
| nps_20250806, NPS Photo |
Aug 21, 2025: on Sunday, Aug 17, the west end of the bridge reached the receiving tower.
 |
| nps_20250821, Jacobs |
Sep 17, 2025: the tower has been removed, and the bridge has been jacked down to its abutment. The bridge seems to go up hill from west to east. That explains why they had a receiving tower and then jacked the west end down. The receiving tower allowed the bridge to be level while it was being shoved across the gap.
 |
| nps_20250917, FHWA |
This is the post that motivated this research.
 |
| Granite Construction posted Innovation moves us forward. We empower our teams to think differently and push boundaries, because that’s what adds value to our communities. Watch this video to learn more about the innovation at our Polychrome Pass Bridge project in Denali National Park: https://ow.ly/57H450XouyQ |
The video is heavy on talking heads saying platitudes and light on information. But this diagram not only confirms that the bridge goes up from west to east, but it also shows the rock dowels and soil nails. And it has a timelapse of the landslide starting at 0:52.
 |
| 4:45 video @ 3:24 |
A bridge collapse in China demonstrates the importance of understanding the geology under your abutments and piers. Fortunately, cracks began to appear in this bridge, and they closed the bridge about a day before the landslide tore the bridge down.
 |
| Casey Jones 4:33 video China Bridge Collapse - November 2025 |
 | |||||
| jeffostroff 14:46 video @ 7:33 | Show chat replay | What Caused China Hongqi Bridge Collapse? Engineers Warned About This |
No comments:
Post a Comment