Geo work on CO 7 rock slide finds more rocks that are loose, extending closure to next week

Travel Advisory

June 23, 2023 - Northeastern Colorado - Crews have already cleared more than 90 percent from original slide

Boulder County — After clearing more than 90 percent of the rocks that slid onto CO 7 between Allenspark and Lyons, geo technical experts from the Colorado Department of Transportation discovered a deeper fracture area on the mountain that will force the extension of the closure through at least the middle of next week.

“Understanding the geology of rock formations is a true science. Predicting when failures occur requires modern technology to measure movement as well as visual inspection. Once the massive rocks were cleared away from the initial slide area, additional fracture lines were exposed,” said Regional Transportation Director Heather Paddock. “These fracture lines have been monitored visually over the past few days and movement is occurring. Geotechnical experts know these rocks will come down naturally in the near future. CDOT’s approach to eliminate the risk and hazard to the traveling public is to remove these in a controlled environment to keep everyone safe.” The rocks in the new fracture area are being brought down by a system that uses air bags in the open crevices that are expanded to bring down the rocks. “That’s how loose these rocks are. We don’t need to blast,” she said. “The only drilling and blasting we are doing is to break up the large boulders that come down so we can haul them away.”

Another 80 truckloads of rock have been hauled off over the last few days to bring the total to about 180 truckloads. In addition to the work on the rock slide, there was scheduled work near the area which is being done during the closure instead of closing a lane at a later date.

“We recognize the impact this closure is having on residents and others who use this road every day,” Paddock said. “But our number one priority is safety and it is clear from the pictures of the site that this is not safe right now. We will be working every day to get the road open as soon as it is safe to do so.”

More details on the rock work needed

As the picture below shows, the original slide not only went over the road, but also stacked up the mountain about 50 or 60 feet up.

The red outline is the chute or failure plane of the slide.

CO 7 rockslide failure plane
After the rocks up the slope were cleared away, the “failure plane” or chute that caused the slide was revealed (in yellow in the picture).
CO 7 rockslide east and west block
A closer examination of that chute shows that it extends behind two large blocks that are at risk of failing. The east block is intact and does not need much work except some stabilization. The west block is very fractured and that is the area that needs to be removed and hauled away.

CO 7 west block fracture

Updates for the closure will be posted to as they are available.

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