As the 2021 road construction season yields to winter, one project enduring year-round is the $343 million reconstruction of Interstate 35 through Duluth's Lincoln Park neighborhood.
Long planned for year-round attention, the winter’s Twin Ports Interchange reconstruction project work will unfold mostly as a spectacle with existing bypasses and workarounds already set in place.
The curving four-lane I-35 bypass through Lincoln Park will remain through next fall, allowing the Minnesota Department of Transportation and its contractors to finish demolition of old bridges, and move on to new work.
“We’ve been able to do a lot of demolition, and we’re projecting to finish that up mid- to late December,” said Pete Marthaler, MnDOT’s major projects manager in charge of reconstruction.
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This week, contractors will conduct bridge demolition work overnight Wednesday and Thursday. The night demolition work is required for the two remaining bridges over BNSF railroad tracks.
Demolition will commence at 7 a.m. Wednesday, and "progress around the clock until the concrete bridge decks are demolished directly overhead the railroad tracks and the fallen debris has been safely removed from the tracks," a news release said.
Demolition work will resume during normal working hours after 7 a.m. Friday.
“Those are the bridges we have to remove in order to finish this demolition phase we’re in right now,” Marthaler said. “We haven’t been able to start, because of the old roadway.”
Once all of the bridges, or elevated sections of ramps and interstate, are down, new piers and bridge substructures will be constructed for the new alignments during the coldest months.
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Also, sheet-pile driving will take place for walls that face the railyard and beyond to Superior Bay.
“It’ll primarily be concrete and structure work,” Marthaler said. “We won’t be doing much earth work, obviously, with the frozen ground.”
Steel sheet piles can be driven using hydraulic rams, and becomes easier once the process is through the first 5-6 feet of frost, Marthaler said.
Concrete pours may seem incongruous with frigid temperatures, but Marthaler explained what makes the process work. But first, he noted that a bridge deck isn’t something that would be poured during the winter. Those are thinner, 8-9 inches, and lose heat more rapidly.
But substructures, like the massive trunks of concrete starting to appear throughout the work zone, are a different story.
“Maybe everyone doesn’t know this about concrete, but curing concrete is a hydrating process, so it creates its own heat,” Marthaler said.
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The contractors from the joint venture between Ames Construction, of Burnsville, Minnesota, and Kraemer North America, of Plain, Wisconsin, will also use blankets over the concrete forms to preserve heat following winter concrete pours.
The bridge substructures include the bridge footings, piers and pier caps.
“Substructures support the deck and girders, and the substructures of the bridge — the footing, piers and pier caps, those types of things — have enough mass to maintain and keep their own heat without freezing,” Marthaler said.
Contractors will monitor the temperature of the concrete-curing process using sensors embedded deep inside the pours, and also 2 inches inside the forms, to give a complete thermal profile of the curing process.
Frozen concrete isn’t the only worry. Too hot, and thermal cracking can start to destroy the concrete form from the inside out.
“In other industries, they’ll use cooling loops in the summertime,” Marthaler said.
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The major bridge substructures being raised this winter will connect I-35 to outlets extending to Superior via I-535, and the Piedmont and Miller Hill Mall areas via U.S. Highway 53.
Also coming to the interchange project this winter:
Process work on design and bid packages for deferred I-535 and Highway 53 work in anticipation of money being appropriated . “We want to be ready if and when it happens,” Marthaler said of accelerating additional reconstruction work on Garfield Avenue and the I-535 interchange on Rice’s Point. The delayed work, including a smoother alignment of I-35 with Highway 53, was originally rescheduled for 2027 and 2028. But the federal infrastructure rollout figures to impact the timeline in a positive way.
Finally, Marthaler noted any additional trench-type activity and more delicate concrete work will be reserved until next spring. For instance, the merging of Coffee and Miller creeks into a 550-foot, four-barrel culvert won’t be re-addressed until spring. Inlet and outlet ends are formed, but the creeks won’t be converged quite yet.
“Miller is still using its old box culvert, and Coffee is using its (underground) stone arch,” Marthaler said. “We’ll make the connection of the creeks at the intersection of First Street and 22nd Avenue West, but that won’t happen until, loosely speaking, a late-April time period.”
Completion of Twin Ports Interchange work is expected in summer 2024.
