Geologists and engineers said Monday that preventing rocks from falling in Glenwood Canyon is all but impossible.
“That location is a bad spot with huge cliffs that go up thousands of feet,” said Ralph Trapani, the former project manager for designing and building the divided highway through Glenwood Canyon, which took from 1980 to 1992. “It’s literally impossible to control all those cliffs.
“Some rockfalls just can’t be prevented. If you do the math on rocks the size of cars falling 1,000 vertical feet, the energies are impossible to stop.”
Jerry Higgins, a geology professor at the Colorado School of Mines who surveyed the state’s highways for the most probable rockfall locations for the Colorado Department of Transportation, said the season for rockfalls has just begun, when daytime temperatures warm up enough to melt the snow. Water runs into cracks in the rocks,then freezes at night. A steady rain fell Sunday night in the canyon.
“When water freezes, it expands and widens the cracks. It’s called ice jacking. Eventually the rocks move enough to where they tumble down.”
To lessen the impact, engineers have long employed rockfall mitigation techniques in Glenwood Canyon, including fences, barriers, netting, rock bolting and covering rocks with concrete.
“We did extensive scaling; we rolled a lot of rocks off these slopes,” Trapani said. “But some of these cliffs are humanly impossible to scale.”
He said the rock face on Interstate 70 on the incline above Georgetown is a good example of scaling and netting done by CDOT. Much of that type of work in Glenwood Canyon can’t be seen from the roadway.
Trapani said the bridge structure where the rocks fell Monday is a concrete deck supported by steel girders, which can absorb much of the energy from the rocks because they’re flexible. Frequently, just the roadbed needs to be replaced and not the steel beams. Rigid concrete beams tend to crack or break, requiring the entire span to be replaced. The beams were still being evaluated Monday.
State Geologist Vince Mathews agreed that rockfalls onto the highway can’t be prevented. Even building rock sheds — steel-reinforced concrete roofs over the highway — might not work because of the size of highway.
But he added, “The odds of rocks falling on you are a lot less than the odds of driving into rocks on the roadway. I never, never exceed the speed limit there, especially around blind corners. I drove over a 5-inch rock once and it cost me $1,400 to repair my car.”
All agreed that CDOT does the best it can to protect motorists. “All those guys working up there are the best in the world at rock mitigation,” Trapani said. “They’ll keep working on this problem.”
Asked about moving the road, he laughed. “The design process was very long. We flew the canyon in helicopters. We did everything we could for this highway. In the long term, this probably can’t be fixed. It’s just a reflection of Mother Nature and a steep, narrow canyon.”
Mike McPhee: 303-954-1409 or email@example.com