What's happening in the white tent along I-35W in Minneapolis?

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Among the ongoing construction on I-35W, a white tent pitched along the interstate near 42nd Street in south Minneapolis gives off an air of mystery to the many motorists passing by.

“A lot of cars drive past here and see the work going on and have some interest in what’s happening,” said MnDOT construction engineer Steve Barrett.

So what exactly is going on?

Barrett says inside the tent, crews are using high-tech method to make sure the storm sewers below the interstate near downtown Minneapolis are fixed, without having to replace them all.

“What’s going on here is we’re doing some rehabilitation of some of the deep sewers that runs underneath the freeway,” said Barrett.

Workers are using giant liners to give new life to old pipes. The large liners are run along a conveyer belt and dropped straight down into the sewer line.

Once that process started on Monday, crews have to keep the operation going 24/7 until it’s completed.

“It’s a resin embedded fiberglass sock, basically that gets strung through the pipe, then the pipe gets pressurized with water and the pipe cures and the end result is a lined pipe,” said Barrett.

MnDOT says there are other sections of sewer line that will be repaired with the liner. They’ve used this process on past projects, but this particular section is unusual because the pipe is so big - about six-and-a-half feet - so it takes a much bigger liner, and more water and steam.

Barrett says re-enforcing the existing pipes with the high-tech liner is cost effective, without interrupting traffic.

“Much less intrusive to traffic, we’re able to do it for less cost and we’re able to get additional life for an old pipe under the road,” he said.

Barrett says the pipe repairs are part of the four-year 35W@94: Downtown to Crosstown project. The goal is to create an improved interstate with less congestion, and better transit connections.

“Definitely thinking about the future, not just traffic, but transit and pedestrians, people crossing the freeway, lots of different improvements in the corridor,” he said.