A look behind the scenes of CDOT’s rockfall mitigation along I-70 (with video)
IDAHO SPRINGS — The Colorado Department of Transportation made a little noise on the mountains overlooking Interstate 70 on Wednesday, blasting a considerable portion of the rock face onto the roadway as part of the department’s ongoing rockslide mitigation work.
Both directions of I-70 were closed Wednesday morning near Idaho Springs as engineers, blasters and maintenance crews with CDOT oversaw the process, an emergency project that jumped to the top of the department’s priority list following a pair of rockslides in the area in late November.
“On the Tuesday before Thanksgiving, we had all that heavy, wet snow that got this slide moving,” said Jeff Hampton, a project engineer for the I-70 Westbound auxiliary lane project, who oversaw the blasting operation Wednesday. “Our geohazard group identified that we needed to get up there and do a blast. But it was the slide after Thanksgiving that caught everyone by surprise. Normally these (rock faces) don’t let go again that fast…
“CDOT’s chief engineer and the executive director have both been involved in this process and said this needs to happen before the holidays. It was really close to Christmas, and we really didn’t want to impact those local communities. But from a safety perspective, we needed to make this happen, so that we don’t have a huge influx of traffic, and then have something happen that we can’t control.”
After the November rockslides, both of which unexpectedly closed I-70 near Idaho Springs, a group of geohazard specialists with CDOT were sent to inspect the area for any other potentially troublesome features in the geography that could pose safety risks down the line.
The team discovered a tension crack — meaning it was beginning to tear away from the hillside — in the rock face at the same site as the last slide. And because the rock was hanging out over other parts of the hill, any slide potentially could have meant big trouble for the roadway and anyone on it.
“It’s clearly hanging out above other rocks, so if it were to slide, it would have come all the way down,” Hampton said. “That’s a big safety issue. So rather than letting Mother Nature decide when she wants to bring it down, we’re going to give it a push.”
Despite the project’s urgency among state officials, the detonation still required a considerable amount of planning given the safety risks involved. Hampton said a crew has been on-site for about a week and a half preparing for the operation.
On Monday of last week, a “blaster” arrived on-site. A blaster is an individual responsible for verifying that reports and photographs of the rock face actually match what they’re seeing in person, and picks out ideal locations to place explosive charges so that the rocks come off the slope in a predictable and controllable manner.
“The blaster owns the site at that point,” Hampton explained. “What he says goes.”
Planning continued Tuesday and Wednesday of last week, while the crews also took some time to placed metal anchors into the rock — set deep into the bedrock to help pulley up equipment like heavy drills to the blast site. The crews drilled deep into the rock beginning Thursday and throughout the weekend — about 15 to 20 feet deep — and set explosive charges into the holes Tuesday. The metal anchors will be removed following the conclusion of the operation.
Once the day of the blast comes around, CDOT closes roads around the area — in this case, Interstate 70 between Silverthorne and Floyd Hill — until the area can be cleared of rocks on the roadway following the explosion.
With the mitigation work completed, CDOT will begin placing mesh netting around the rock face to prevent any further loose rock from falling: one snug right up against the hill to help it hold its place and another to catch anything falling from above.
In all, dozens of CDOT workers are involved in the process.
“We call in a bunch of help anytime we do a road closure,” Hampton said. “The CDOT engineering staff comes out to help man those closures and help make sure everything is closed off for the safety of our public, and the safety of our maintenance guys down the roadway. … It’s all about safety. Whole system whole safety — those are the buzz words right now for us, and we live and breathe it.”
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