The rocks that are intentionally crashing down the Rims from six troublesome spots above Zimmerman Trail are tumbling ahead of schedule.
Some rocks are being treated to the opposite fate — they’re being bolted down with fasteners that are an inch in diameter and up to 35 feet long.
Paul Rieger, who’s managing the $718,219 rockfall mitigation project for the Montana Department of Transportation, said this week that the project contractor, GeoStabilization International of Grand Junction, Colo., is ahead of schedule and has pared crews’ work schedules down to six 10-hour days per week from a seven-days-a-week schedule.
Scaling — the cleanup of relatively smaller rocks — is about 50 percent complete, Rieger said. Workers expect to wrap up the project sometime during the week of June 9, he said, slightly ahead of schedule.
After that, it will be up to city street crews to repair road damage done by the March 25 rock slide and replace damaged guardrail before reopening the closed portion of Zimmerman Trail.
Crews from Terracon, the consulting engineers called to the site following the slide, have mapped the cliff face, Rieger said. “They identified all the plates and the rock blocks, all the rocks that needed to come down,” he said.
In order to safely bring the rocks down — some in dramatic fashion, others less so — GeoStabilization International crews have erected earthen berms to protect Zimmerman Trail, the gas utility beneath it and nearby homes.
“It’s pretty entertaining” watching, from a safe vantage point, some of the rocks tumbling down, said Rieger, who’s at the worksite every day. “I haven’t giggled this much at work in a long time.”
Rieger has been documenting what he's witnessed, both with still photos and short video clips. In one, workers have drilled into a large rock face and inserted an airbag. Inflate the airbag and drive into the rock with a really big tire iron-like device, and the rock face comes down quickly and loudly.
As a safety precaution, six homes will be briefly evacuated before rocks are brought down from sites on the eastern side of the affected area. Those residents have been contacted and will be out of their homes only for a few hours one day next week, Rieger said.
Most onlookers have managed to stay away and let the crews work, he said, but a few joggers had to be told recently that even a fast run along the trail constitutes trespassing. One persistent runner was given the choice of finding another jogging trail or facing arrest; the runner took the former, Rieger said.
“We have done our best to persuade them,” Rieger said. "But, we’ve had to tell some of them, ‘Hey! We’re scaling now. We’re bringing big rocks down.’ ”