Cracks that grew into a hole in the Denver-bound lane of the U.S. 36 were expected to keep the roadway closed to southeast bound traffic at least through July 16 while the Colorado Department of Transportation works to shore up the ground alongside the road.
Highway officials urged people commuting between Boulder and Denver to rely on public transportation, offering free rides on the Flatiron Flyer and the LD bus routes on July 15 and 16.
Josh Laipply, CDOT chief engineer, said the cracks occurred in the roadway just north of where it meets a bridge over a set of train tracks. The bridge and the northwestern Boulder-bound lanes were not affected, he said.
“The bridge supports are buried deep, they won't move,” Laipply said. “The part that moved is on the ground underneath the roadway.”
Engineers suspect that the ground on the western side of the roadway subsided some 30 feet below the ground level, possibly from recent heavy rain and runoff.
“We are looking at a pretty large slope failure on the ground below U.S. 36,” Laipply said. “I don't anticipate the road will be open by the workweek, but we are doing a lot of data analysis and collection to figure out what the best solution is and we hope to bring on contractors to do the work soon.”
Dump trucks and loaders were covering the ground on the western side of the roadway with dirt in an effort to counterbalance the shift — a short term solution, Laipply said.
“About 30 to 40 feet below the ground there is a level of clay, and it's more slippery,” he said.
He said crews Saturday noticed a bulge in soil just west of the highway where slope had subsided.
The longer term fix will be to bury caissons in the ground west of the roadway, creating deep concrete columns to halt the ground shifting and prevent future slides. Laipply said the highway department was taking work bids over the weekend from three contractors to put in the caissons.
Once the road's supporting soil is shored up, Laipply said crews will start mending the roadway itself, filling the crack and replacing the pavement. The original top layer of the road was concrete, Laipply said, but it would likely be replaced with asphalt.
Cracks on Thursday
Laipply said transportation department officials noticed cracks on the pavement on Thursday July 12 and began monitoring them. By Friday afternoon, the cracks and widened enough close all but one lane of the road between Wadsworth Boulevard and Church Ranch Boulevard.
The cracks continued to widen over the weekend, leading the department to completely closed the southeastern-bound road completely.
The situation continued worsening by Sunday morning, turning the crack into an actual hole, and the department is considering having to rebuild the roadway completely and considering alternate detours around the road - possibly moving the southeastbound traffic to share the northwestbound lanes.
“If you are driving between Boulder and Denver, don't use 36,” Laipply said. “Use Highway 7 (through Lafayette) or Highway 93 (west of Arvada). And of course, there is Northwest Parkway.”
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