Vermont transportation officials led a delicate operation on a high rock ledge in Royalton Thursday, aiming to reduce the chances of a damaging rock slide happening on that stretch of I-89 southbound.
Traffic was brought to a series of standstills in what is known as a "rolling roadblock," while a state contractor used a piece of heavy machinery to push loose dirt and rock from the ledge, so it tumbled to the ground below while no vehicles passed on the interstate.
"This is definitely out of the realm of maintenance," said Chris Bump, the district’s project manager for the Vermont Agency of Transportation. "This is more responding to a small emergency."
The small emergency Bump referenced occurred April 21 when a significant amount of stone fell right onto the highway, forcing the temporary closure of one lane of travel while the mess was cleaned up. No one was injured.
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Also last month, on I-89 North in Richmond, a boulder the size of a pickup truck came careening down.
"It was a good-sized chunk," Mark Meunier of VTrans told New England Cable News on April 10. "I haven't seen one that big that's come down, so it was a little bit of a surprise to me."
In mountainous Vermont, the highway winds past craggy rises in many places, so VTrans stays watchful of the potential for slides from rocky ledges. The Royalton work is preventive, following the agency labeling the stretch a trouble spot because of the problems in April.
"You always want to be aware," VTrans geologist Tom Eliassen told necn. "There are times where we need to act right away to protect everybody."
Eliassen explained preventive work occurs regularly throughout the year. He said the contractor Thursday was primarily getting rid of weak soil and loose stone. All of it could otherwise fall on its own during a rain storm, Eliassen said.
Cycles of freezing and thawing, where water gets into cracks in rocks and then freezes, are a prime contributor to rock slides, Eliassen said. Another common trigger is the growth of trees on ledges, he added. Tree roots can work their way into the stone and weaken it, Eliassen explained.
Scott Rogers, the director of the VTrans operations division, said he knew of no deaths or serious injuries in Vermont caused by rock slides. He said there have been some major rock slides involving massive boulders, but none that caused loss of life, to his knowledge.
Rogers noted that vehicles and other property have occasionally been damaged by bouncing stone or chunks of rock on highways.
Eliassen said the state plans more ledge work in Royalton and in other spots that are prone to rock slides, to cut the risk of damage to passing vehicles.