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Highway project includes unique fence

Products designed to take impact of falling rocks

 

August 1, 2019

Annie Wooden

ROCK FALL FENCING being installed along Highway 200 east of Thompson Falls is secured by anchors on top and on bottom (as seen above) that are drilled 25 feet deep into the rocks.

Driving through the Highway 200 construction project east of Thompson Falls this spring and summer has offered views of cranes, excavators and crews scaling rocks. The mesh fencing being constructed looks like oversized chicken wire, but as The Ledger found out this week, there's a lot that goes into securing rocks and the fencing.

Montana Department of Transportation project manager Ryan Paulsen and Kevin Cichy with Triptych Construction of Oregon provided more details about the rock fall fencing being placed. Travelers have been able to see Triptych placing 12-foot posts on top of the rocks along the construction project. Those posts are put in place by four bolts that are drilled into the rock 25 feet deep. The cables that anchor the posts are also drilled into the ground 25 feet, Cichy said. From there, steel cable netting is strung from the posts and secured to the rocks. In one section of the construction where the rocks are nearest the roadway, the fencing will be secured with anchors that also go 25 deep into the side of the mountain.

Cichy and Paulsen said a lot of planning went into designing the fencing for the Highway 200 project. Cichy said engineers look at the landscape and study the size of rocks that typically will fall into the road. They then calculate the amount of energy from falling rocks to determine what impact the rocks will have on the fencing. The engineers design the rock fall fencing from there. In the case of the Highway 200 project, larger steel cable fencing is first placed to take the impact of larger rocks. Then a smaller fencing with openings a little more than two inches is placed over to catch any other falling rocks.

"The impact is similar to when a volleyball is thrown into a net," Cichy explained. The anchor cables have integrated brakes to absorb some of the impact of falling rocks.

Annie Wooden

SAFE PASSAGE - Paving is set to begin on the Highway 200 construction project this week. With that, the detour around the new wildlife underpass bridge will be removed and the underpass will be finished and additional fencing added.

Paving began this week on the project, and Paulsen said it will take about four days before traffic is able to travel on the pavement. Then the guard rail and chip sealing will be completed. Paulsen also noted that the detour around the area where the wildlife underpass bridge was installed will be removed and the wildlife fencing will need to be placed in that area. The wildlife deterrent mats at each end of the project also need to be installed. Paulsen said the paving piece of the project will take about two weeks, and it was a bit behind schedule due to crews being delayed by weather on another project. Cichy also said that the rock fall fencing portion of the project should be complete in two weeks.

Triptych Construction currently has seven people working on the project. Last fall, they and primary contractor LHC, Inc. worked to remove rocks from the hillside before the construction began this spring.

More information on the project is available at http://www.mdt.mt.gov/pubinvolve/east-thompsonriver, or text TRIVER to 22828 to receive updates via text message.

 

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