About $2 million in repairs start this week on an 80-ft-long crack in the roof of Interstate 70’s Hanging Lake Tunnel through Glenwood Canyon, Colo. The crack was discovered during routine maintenance last July and became more pronounced in February, when it began to leak.
Colorado Dept. of Transportation officials then shut down the 15-year-old tunnel that carries 17,000 vehicles a day on this narrow stretch 158 miles west of Denver.
CDOT officials say that the crack was probably caused by a 2004 rock slide that brought more than 2 million lb of rocks down. The tunnel consists of two separate two-lane bores, each 3,900 ft long. The crack appeared in the 105-ft-long transition section at the midpoint of the eastbound tunnel, a concrete box culvert with a roof section is more than 4 ft thick.
“It’s that ceiling slab that failed,” says Dick Brasher, vice president of Concrete Works of Colorado Inc., the Lafayette, Colo.-based repair contractor. Concrete Works has completed shoring work and started excavation of the nearly 8,000 cu yd of rocks on top of the tunnel.
“We had equipment up there within three days after we got the go-ahead, but excavation will be tricky because there’s just no room to stockpile material,” Brasher says. “We’ll have to take all of the rocks and dirt out by railcar, then bring the dirt back in by rail after repairs are done.”
Preliminary design calls for leaving the failed slab in place and attempting a “sandwich repair” above and below it, Brasher says. Work is to be complete by October.
Crews will drill holes through the ceiling slab every 2 ft in a grid pattern. Then, they will insert steel rods through the holes, extending through the damaged slab to reinforce it. Shotcrete will be pumped in under the cracked slab from inside the tunnel and a new slab poured from above to create a composite structure 6 ft to 7 ft thick.
