Innovative approach keeps reconstruction in fast lane

Photos Courtesy of John Yost at Marble Street Studio

Poor soil conditions threatened to extend a four-year interchange reconstruction into a six-year project. U.S. 41 and Highway 29 cross in Green Bay, but the interchange was too small for its projected traffic and resulted in high-speed freeway traffic merging with slower traffic on the state highway.

“You had two different traffic users, you know, essentially blended together, and it was a very inefficient setup,” said TJ Dougherty, project manager for HNTB Corp., the project designer.

The 3.9-mile reconstruction design included eight roundabouts and 26 bridges to help separate the traffic and better serve all users, including bicyclists and pedestrians. Because of the scale of the project, HNTB devised a schedule that would allow work to build off itself in a series of more than 60 phases while limiting the disruption to travelers.

“Coming up with that right order of projects was a huge challenge of balancing all the different needs we needed to meet,” Dougherty said.

But that project schedule depended on crews meeting hard deadlines, and poor soil conditions threatened to cause massive delays and a ripple effect that would push every other phase off schedule. If crews had excavated the soil, they would have had to dig as deep as 30 feet in some areas, which Dougherty said would have been too expensive. But waiting for the soil to settle could have added as many as two years to the project, a delay HNTB was not willing to impose on the public.

“That’s a very, very tough sell to go down that road,” Dougherty said.

Working with the project’s owner, the Wisconsin Department of Transportation, HNTB decided to bring in an out-of-state subcontractor to install wick drains, a method of pulling moisture out of soil as construction progresses. The subcontractor installed a system of tubes that were 1-inch wide and varied from 30-feet to 70-feet long. The tubes, of which the subcontractor installed more than 100,000 lineal feet, were spaced 5 feet apart and then buried under a layer of gravel called a drainage blanket. The road surface was then laid over that drainage blanket, and the weight of those materials slowly forced the moisture out of the soil and up through the pipes. The process is not common in Wisconsin, Dougherty said, so the decision entailed some uncertainties. However, it worked, and the project remained on schedule, saving the owner from a significant extension.