Around midnight early in March, a rock slide gave Interstate 70 a one-two punch, closing a 17-mi. (27.4 km) stretch of the highway. Boulders punched two gaping holes in a bridge and the roadbed, leaving huge rocks strewn all over the pavement near Hanging Lake Tunnel in Glenwood Canyon, Colo.
In the deep, narrow chasm about 110 mi. (177 km) west of Denver, some of the lanes of I-70 that wind through the Glenwood Canyon will remain closed until sometime in mid-May as crews work to repair damage. The rocks and boulders, including one that weighed 66 tons (59.9 t), crashed onto the highway earlier this month closing most lanes, except two—one in each direction which are open to traffic.
The Colorado Dept. of Transportation (CDOT) has reduced the speed limit to 40 mi. per hour there and loads wider than 14 ft. (4.26 m) are prohibited from traveling through the work area.
Flatiron Construction of Longmont, Colo., the lowest of four bidders, began working on repairing the damage to the highway. Flatiron’s figure of $860,417 is only part of the cost, which is expected to be much higher when emergency response, blasting and traffic control costs are tallied. CDOT said it is still working on those figures but estimates it will be approximately $1.5 million.
About 20 boulders ranging in size from 3 to 10 ft. (0.9 m to 3.0 m) in diameter crashed onto the road just after midnight on March 8 tearing holes in the elevated sections of the highway. The CDOT estimated the largest of the boulder weighed 66 tons.
The biggest hole, about 20 by 10 ft., (6.0 m by 3.0 m) was torn in the westbound lanes, which are closest to the hillside. Another hole about 6 by 6 ft (1.8 m by 1.8 m). was created in the lower eastbound lanes. “There were just dozens of other boulders ranging in size from footballs all the way up,” Stacey Stegman, a CDOT spokeswoman, said. “And then there are many divots and rocks embedded in the road,”
The falling rocks and debris also damaged the guardrail in the area as well as the median barrier.
No vehicles were involved in the slide and no one was hurt, Stegman said. “We were thrilled,” she added. A CDOT employee saw the boulder come down on a traffic camera in the area. “It was really hard to see because it was very, very dark at that location,” Stegman said.
While CDOT crews began clearing operations quickly, officials had to check the hillside to make sure more rocks weren’t ready to fall.
“Getting the road open was pretty quick but it was painfully slow at times with some of the geologic issues we were dealing with,” Stegman said.
Crews spent two days blasting the larger boulders into smaller pieces to get them off the road, she said. “Then the biggest concern we were dealing with was a 20-ft. boulder still up on the mountain that our geologist determined was unstable,” she said. “They didn’t feel comfortable letting traffic travel] under it.”
“The CDOT geologist and a team of contractors scaled the hillside to determine how to get the boulder down,” Stegman said. “Just getting to the boulder was a feat in itself. It took crews two hours to ascend the hillside,” she said.
Using a tool that is like a bigger version of a crow bar, the crew, hanging on ropes and rappelling on the hillside, tried unsuccessfully to bring the rock down, Stegman said.
When that didn’t work, they had a helicopter fly in drills and a generator the next day, she said. “They drilled all day long and packed it up with explosive and then were able to bring it down the mountain,” she said.
Since the blast broke the boulder into smaller pieces, no additional damage was done to the road, she said.
Crews cleaned up the results of the blast, did some drainage work, repaired the roadway, got traffic control in place and were able to open two lanes of traffic, Stegman said.
The road closure was a major inconvenience to travelers because alternate routes would take them “a couple of hundred miles” out of their way, she said. Motorists could take Highway 50 over Monarch Pass or north on 13 to Steamboat Springs.
Still, motorists were very understanding about the situation, Stegman added. “We got a lot of coverage on it so people really planned well and took the alternate routes. I know there was some frustration. I’m shocked actually at the amount of positive feedback we got. I think there was a lot of understanding once we got pictures out there of what we were dealing with. People were much more understanding than I think they would have been otherwise.”
While rockslides are not unusual in that part of Colorado, they usually aren’t so big and don’t do as much damage, Stegman said. Holes from a similar rockslide on Thanksgiving 2004 caused $1.2 million in damage, she said.
“It’s unusual to see them this size but we do have frequent rock falls in the canyon,” she said. “It’s unfortunate but rock comes down in these areas.” The rocks are old and the freeze-thaw cycle can loosen their hold, she said.
“It’s normal. It happens frequently, unfortunately but not often does it hit the highway,” she said.
With the size and weight of the largest boulders involved in this slide, the damage could have been worse, Stegman said.
“Thankfully we have a very tough bridge in this area,” she said. “The bridges are built with a lot of strength so more damage wasn’t done.”
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