Sinkhole repairs begin near Leadville
July 19, 2012
Highway-sucking sinkholes are a lesson in perspective.Concrete trucks look huge when you’re following them on your Vespa, but put them beside the gash in the earth along U.S. Highway 24, and they look petite.Concrete trucks on Wednesday started pouring thousands of cubic yards of material into the so-called sinkhole that closed Highway 24 between Red Cliff and Leadville. The hole is not technically a sinkhole because it caved in over an old railroad tunnel.”People wonder if we were being too conservative closing the road,” said Stacey Stegman, one Colorado Department of Transportation’s public-relations crew.They’re not.The hole has expanded and is now 35 feet by 35 feet and 100 feet deep. There is less than a foot of earth under part of the road, and that bit of earth is barely hanging on – a ballroom dance couple could knock it down.A bunch of rock and dirt apparently lost the will to live and fell from the bottom of the road surface into the hole during Wednesday’s media tour.No one’s exactly sure when the sinkhole sank. All CDOT knows for sure is that a maintenance crew rolled by there on the afternoon of July 7 and everything was fine. Another crew rolled by at sunrise July 9 and noticed that a large chunk of terra firm wasn’t all that firm and wasn’t visible to the naked eye.They had themselves a sinkhole.It fell into a Denver & Rio Grande Railroad tunnel built in 1890 to haul silver ore out of the mines. The railroad company used it until the 1940s, when a new reinforced concrete tunnel was built nearby. Trains stopped using the tracks in 1998.That abandoned tunnel loops under Highway 24 in two other places.When the tunnel was abandoned, the timbers began to deteriorate and bits of the roof began to fall, said Joseph Elsen, CDOT program engineer. Over the years, it created what looks like a chimney and the hole finally made its way to the surface, right under Highway 24.Elsen is one of CDOT’s more experienced hands. This is his ninth emergency of this type.”You walk up to something like this and wonder, ‘What on earth do we do?'” Elsen said, adding that they don’t wonder that for long.They put the repair specifications together in about two days. Because it’s an emergency, they bid it out to four firms that handle this sort of thing. Those bids went out around 5 p.m. Friday. By Monday night, CDOT had selected Hayward Baker, and the firm was rolling to the sinkhole site by Tuesday morning.CDOT dropped an incentive clause into the contract: Hayward Baker gets $5,000 per day for every day they beat their Aug. 6 deadline. They would pay $5,000 CDOT per day for every day they miss it.CDOT expects to pay; Hayward Baker expects to collect, and crews are working from 6 a.m. to midnight to see to it.
Cleaning up these kinds of messes is all Hayward Baker does. The Highway 24 hole is massive, but the crew has plugged worse, said Joe Harris, with Hayward Baker.When rockslides closed Dowd Junction in 2008, CDOT called them. When that huge boulder crashed through the Interstate 70 bridge in Glenwood Canyon, they were called again.They’re in Rock Springs, Wyo., right now cleaning up a collapsed mine. They’re a regular presence around Colorado Springs when this sort of thing occurs, too.Harris’ first job with the company was shoring up the foundations under the Chambertin condos in Avon. The buildings were sliding down the hill toward I-70.”Our company’s motto is that you may not be able to see our work, but you can have confidence when we were there,” Harris said.
For this job, crews are drilling underground from the north and south sides of the highway to construct containment barriers made of grout that dries hard. The walls are about 40 feet from each side of the highway.Concrete trucks are pouring a thinner grout material into the void, followed by a pressurized grout to fill any gaps. That will compress the material under the highway and strengthen the roadway platform, explained Matt Figgs, CDOT’s project manager.Once everything is stabilized, crews will mill and pave the road. Those trucks are dumping about seven cubic yards of material every time they back up to that sink hole.They’ll drop more than 300 truckloads into the sinkhole, calculated Elsen, who pointed out that the trucks can hold nine yards of concrete. They don’t, though, because fully loaded trucks are heavy and they’re backing up to a sinkhole that might, well … sink.