Christmas came early for Colorado Department of Transportation geohazards geologist Regan French when she learned rocks careening off cliffs above Colorado Highway 3 had damaged a retaining fence designed to keep them from reaching the road.
Colorado Highway 3 – the old two-lane asphalt road that snakes alongside the Animas River on Durango’s south end – served as the city’s main entrance until the South Camino del Rio segment of U.S. Highway 550/160 was completed in 1980.
Rockfall is common along the sandstone cliffs on the road’s east side and is a hazard the Colorado Department of Transportation must manage to keep motorists safe.
“It was like a day or two before Christmas, because the email that my boss was sent said ‘Santa brought Christmas a little early,’” French said with a laugh. “A bunch of rocks had fallen. I was able to get out here the following week, right before New Year's, to take a look at it. That’s kind of when the planning started.”
The retaining fence – constructed of heavy metal posts anchored into the slope supporting a burly metal curtain that catches falling rocks and directs them downward, behind a concrete barrier – had worked as designed.
But rocks struck one of the support posts, French said, and it needed reinforcement.
“It took some damage, but it still performed as designed,” she said.
French’s job was to plan how to mitigate the risk of rocks falling onto the road, repair the retaining fence and remove rocks from a ditch beneath the cliff.
That involved taking photos of the slope, evaluating risk and working with a fabricator to make a new support post.
All that planning culminated in CDOT closing the southern portion of the road Monday for two weeks so crews could safely mitigate rockfall.
“I got out here on Monday,” said French, who’s based in Denver. “We’re keeping the road shut for the entirety of this, because it’s not really safe for anyone to travel while this fence is completely open.”
CDOT spokeswoman Lisa Schwantes said the department is overseeing the project and working with Apex Rockfall Mitigation LLC, based in Grand Junction.
On Wednesday, workers tied themselves off with a two-rope rappel system to tree anchors and dangled themselves over the sandstone cliff looming above Highway 3. They worked methodically, using their feet, hands and big steel bars to jimmy loose rocks free and send them careening down the cliff face.
Dropping loose rocks is the first phase of the project, French said. That makes it safer for workers repairing the fence, who will drill new anchors for the metal posts supporting the retaining fence.
“The next phase, we’re going to simultaneously drill rock anchors for those new posts and downsize that rock,” French said. “We opted to do the downsizing with an excavator with a breaker mounted onto it so that the person in the excavator can work while the guys on the slope are drilling.”
Workers will drill into the hill at an angle to set the new posts, which will then be secured with grout and cable anchors, French said.
She said Colorado has a large amount of rockfall hazard mitigation, because of how mountainous the state is.
“Colorado has got to be one of the No. 1 states that has to deal with rockfall mitigation,” French said.
She said that amount of rockfall management keeps her and her team at CDOT’s Geohazard Program busy. According to the program’s website, the team “provides expertise in the geotechnical engineering and geohazard fields,” which helps “direct the planning, design, construction and maintenance of civil engineering and environmental projects for CDOT.”
Part of that, French said, is cataloging every slope across the state to better understand how to manage them.
“We are actually building an asset management platform and inventorying every single slope across the state to help us make decisions about where makes the most sense to work on and put up a fence based on mobility and safety,” she said.
French said her team’s work is meant to keep roadways safe. CDOT shut down Highway 3 to ensure no residents were put in danger during the work.
At the same time, Schwantes said, CDOT is able to perform other maintenance work on Highway 3. While the road is closed, crews have been able to seal cracks in the road surface with asphalt.
The project is expected to wrap up March 20.
sedmondson@durangoherald.com
