When traffic delays occur again at entrance to Aspen, motorists can thank conservative engineering
When you are sitting in traffic on your way in or out of Aspen next week as repairs are made to the Castle Creek Bridge for the second time in a year, know that it’s because the engineers on the project are trying to ensure your safety and prevent the bridge from collapsing.
Traffic will be detoured and delayed Monday and Tuesday from 7 a.m. to 7 p.m. as crews finish pouring concrete and resurfacing the road after repairing a large pothole due to drainage problems.
The work was scheduled to be completed this week but was postponed due to weather.
City Engineer Trish Aragon said the engineering firm hired by the city, Otak, was conservative in the amount of asphalt that was laid down when the bridge was redone in 2018.
Otak’s concern was too much asphalt would be too much weight on the aging bridge that now has an 8-foot-wide concrete sidewalk, which was one of the main improvements to the project.
“Structural engineers, like all engineers, are very conservative because their license is on the line,” Aragon said. “It may not be practical in some situations.”
It turned out Otak’s requirement of 1½ inches of asphalt isn’t enough to slope the road and prevent pooling on a flat bridge. As a result, the road surface peels when water builds up.
Aragon said she and others were concerned about weight and thickness of the road’s surface at the outset of the project, knowing that it’s an old bridge.
“Whenever you get into old infrastructure you have problems,” she said. “There is no one to blame, it’s just that the bridge is old.”
When a large pothole emerged this past spring after the bridge had been open for the winter, city crews filled it with temporary material knowing that the problem would likely occur again, Aragon said.
“We went back to the structural engineer and said ‘This isn’t working,’” she said. “It’s hard to retrofit something that has been around for 50 years.”
Otak resurveyed the bridge and determined going to 3 inches of asphalt would be OK in certain areas of the road, Aragon said.
“We have a cross slope now,” she said.
Pete Loris, Otak senior vice president, said the engineering team assessed the load rating of the bridge and they were comfortable with between 1½ inches and 2 inches.
But after seeing the drainage problems, Otak and other engineers agreed to take the asphalt to 3 inches, but that “pretty much puts it at the limit of the bridge.”
He added that it’s difficult to determine what the construction tolerances will be on an old bridge like Castle Creek. But it wasn’t a best guess scenario — the assessments are based on engineering judgment taking into account the information available at the time.
Aragon said concrete, which lasts longer and is not as easily prone to potholes as asphalt is, will be poured on portions of the bridge near the abutments to prevent further damage.
Additional costs for this fall’s work are built into the project’s contingency funds, but the dollar amount was not immediately available Thursday.
Aragon said Otak is not charging the city for its work on this go-around. But the city is paying for additional costs associated with public outreach and traffic flaggers.
As part of the $4.65 million contract with Gould Construction approved by Aspen City Council in 2018 prior to the project, which disrupted traffic for four months last year, Otak is an engineering consultant to the city.
“We appreciate everyone’s patience at this time,” Aragon said. “We are trying the best we can.”
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