Raining rocks create challenges on Idaho highways

From The Star-News
McCALL - A rock slide about three miles north of Banks on Idaho 55 closed the highway from around noon on Sunday until about 5:45 p.m. on Monday.

Idaho Transportation Department crews worked on Monday to remove loose rocks from a hillside three miles north of Bank.

Debris had been falling from the mountainside for three or four days, but around 10 a.m. Sunday the hillside shifted and debris slid over the guard rail and onto the highway, said Dan Davis, the ITD supervisor for Banks and Cascade.

"It got to the point where it was too unsafe to have traffic on the road and that is why it was closed," Davis said.

Those wanting to go from McCall to Boise had to travel through Council using U.S. 95 which increased the trip by about 50 miles and 40 minutes, according to MapQuest.com.

Davis was called to the slide about 2 a.m. Sunday and found several 1,000- to 1,500-pound boulders in the road along with other debris.

Crews kept the road clear until about 10 a.m. when more debris began falling, he said. On Monday, 1,300 tons of rocks and dirt were removed from the shoulder of the road.

Another 700 to 800 tons slid onto the shoulder Monday night, but did not slide onto the highway and was able to be removed on Tuesday with one lane of traffic open, Davis said.

A loader and track hoe was used to load the material into dump trucks that hauled it to a site about one mile south of the slide, Davis said.

"The goal was to create an even slope and enough space between the highway and the mountainside for debris to gather when the mountain slides again," Davis said.

A rock scaling crew also worked next to the slide and knocked loose rocks from the slope to help prevent another slide, Davis said.

"The amount of moisture in the ground created the perfect storm for the slide to happen," Davis said.

The weather on Saturday was 70 degrees and sunny, which thawed the ground and saturated the clay layers underneath to caused the slide, he said.

From ITD reports
GRANGEVILLE - A rockslide about 10 miles west of Elk City early this week reduced Idaho 14 to a single lane of traffic near milepost 39.
The highway, often used on weekends for recreation travel, remains open to travel, but motorists are urged to use caution while driving through the area.
ITD crews expect to continue removing rock and debris for the next two weeks. During daytime operations, flaggers will direct traffic through the slide area. Motorists should expect daytime delays. The area is marked by signs during non-work hours and on weekends.
The slide occurred Monday, April 4. It covered the highway for about 100 feet to a depth of about 20 feet.
Motorists are urged to watch for rocks or debris on any state highway next to steep slopes. The freeze-and-thaw cycle combined with spring rains can make slopes unstable.

Photos: Idaho 55 was reduced to a single lane (top) this week after a Sunday rockslide that resulted in a 30-hour closure. Crews from Western Construction helped clear debris from the highway (above, right). Pictured lower right is a rock scaler from the contractor's crew adjacent to the slide area.

Published 4-8-2011