Top stories of 2007: Hanging Lake Tunnel closed |

Top stories of 2007: Hanging Lake Tunnel closed

Pete FowlerGlenwood Springs, CO Colorado
Kelley Cox File Photo Post Independent

GLENWOOD CANYON – Only two lanes instead of four for highway traffic through Glenwood Canyon were open over the summer.

The eastbound bore of the Hanging Lake Tunnels closed for more than six months after officials discovered a 70-foot-long crack in concrete above the tunnel. It stretched through a 412-foot thick slab of concrete that weighs about 3 million pounds.It’s thought to have been started by rockfall in 2002 from a rock outcropping that towers hundreds of feet above the eastern side of the five-story command center that sits between and above the tunnels.

The Colorado Department of Transportation closed the eastbound lanes March 30 and began diverting a lane of traffic through the westbound bore. The eastbound lanes didn’t open up until October.CDOT said repairing the crack cost somewhere in the neighborhood of $6 million. About 25 million pounds of dirt was excavated to get 30 feet down to the roof of the tunnel from above. With supports in place, concrete was laid down above the damaged slab, and “shotcrete” – concrete sprayed from a gun – was shot onto the slab from below. Steel bars were used to connect the two layers through approximately 1,000 holes drilled through the original slab or nearby spots, according to CDOT.

Large foam blocks and layers of “geo-textile grid” were put down above the concrete instead of merely replacing the excavated dirt and rock. The foam and rubber webs are designed to help reinforce the soil and spread energy from potential rockfall over a larger surface to avoid further damage.CDOT plans to keep an eye on the tall rock outcroppings to monitor possible future rockfall.

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