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Mike Nowatzki, Published July 16 2009

Main Avenue project hits snag in West Fargo

After wreaking havoc during spring flooding, the Sheyenne River is at it again – only this time, it’s causing a major headache for crews working on West Fargo’s Main Avenue reconstruction project.

The snag could prolong work that is forcing traffic on the city’s main east-west avenue into single head-to-head lanes and significantly limiting access to at least one business.

The frontage road on the south side of Main at the Sheyenne River bridge remains closed, forcing motorists to go around the block to reach Petro Serve USA, formerly Dan’s Oil.

Assistant Manager Jon Shannon said store officials were told the frontage road would be out of service for two weeks, “and that was two weeks ago.”

“It’s really hurt our business,” he said. “We don’t get any random stoppers-by anymore.”

Crews have hit a roadblock in replacing the Main Avenue bridge over the river with a box culvert.

The situation is such a mess, subcontractor Industrial Builders wants to scrap the box culvert.

“What we’d like to do is see a bridge go in,” company president Paul Diederich said. “I think a bridge is constructible. I don’t know if a box (culvert) is constructible.”

To create a dry work site, Industrial Builders built a cofferdam – a channel with metal sheet pilings for walls – to divert the river around the culvert construction area.

But the fast-flowing river, swollen from heavy rains, scoured the clay bottom of the channel, also called a flume, said Joe Peyerl, project engineer for the North Dakota Department of Transportation.

“Basically, the (water) velocities were such that it eroded that away and somewhat compromised the integrity of the flume where it wanted to kind of cave in,” he said.

The flume has since been plugged, and the river is flowing through its natural channel again.

Diederich said the main problem isn’t the river flow but rather loose soil that caused the pilings to shift, despite some being pounded 45 feet into the ground.

“We’ve done work in lots of different soils, and I’ve never seen soil that liquefies like that before,” he said.

“The soil is very light, and it’s not very cohesive,” Peyerl said.

Engineers are evaluating how to stabilize the cofferdam and the ground around it, Peyerl said.

Shoring up the cofferdam would be extremely complex and time-consuming, Diederich said.

In the opinion of Industrial Builders’ engineers and other engineers the firm has had look at the situation, a box culvert is “probably not a very timely solution,” Diederich said. Officials also must consider the cost to taxpayers and inconvenience to motorists, he added.

The box culvert and associated work was bid at $1,083,000. A bridge would be more expensive, Peyerl said, offering a ballpark estimate of $1.4 million.

“Nothing’s impossible,” Peyerl said of the box culvert. “But with some soil problems and some issues that we’ve seen now, is it the clear-cut best decision? That’s what we’re trying to find out.”

The box culvert was chosen over a bridge for several reasons, including the lower cost, less maintenance for the city, aesthetics and “wing” extensions that will serve as retaining walls along the river channel, Peyerl said.

The Sheyenne River diversion around West Fargo also ensures that the culvert, which will have two 12-by-12-foot openings, can handle the river flow through the city, he said.

The river flow was about 700 cubic feet per second when it was diverted on June 26, Peyerl said. The flow was around 445 cfs on Tuesday, according to the U.S. Geological Survey.

“It is a big range, and it is an unknown variable that makes it kind of more of a difficult project to build these structures, (in) that you never quite know what those velocities are going to be,” Peyerl said.

Main Avenue is being rebuilt this year from Fifth Street West to Sixth Street East, the first phase of a three-part project. Dakota Underground Co. of Fargo is the general contractor.

This year’s work is expected to cost $8.7 million. Traffic is one-lane in each direction through the construction area.

It’s not yet clear whether the cofferdam setback will add to the project’s cost or delay the culvert’s completion, now slated for the end of October, Peyerl said.

“We hope by the end of the week … to have a complete analysis of what we’re really dealing with and move forward,” he said.

Readers can reach Forum reporter Mike Nowatzki at (701) 241-5528