Replacing and rehabilitating aging structures on Highway 61 north of Two Harbors, Minnesota, requires careful measures to deal with Lake Superior storms, hard bluestone, stream restoration, and a bridge listed on the National Register of Historic Places. Minnesota-based Northland Constructors of Duluth, Inc., started the $12.63 million Silver Creek and Stewart River Bridges project in fall 2021 and expects to reach substantial completion in fall 2023.

The bridges are part of the scenic, two-lane Highway 61 route along Lake Superior’s shore. Northland is replacing the box culvert constructed in the 1930s at Silver Creek with a new concrete bridge. At Stewart River, crews will rehabilitate the Classical-Revival-style, concrete-arch bridge – originally constructed in the 1920s, then widened in 1939 – to carry one lane of Highway 61. A new concrete bridge inland of that historic structure will carry the other travel lane. Reconstruction on both sides of the bridges rehabilitates the pavement and accommodates new alignments.

Financed with 80 percent federal and 20 percent state funds, the project not only upgrades the aging structures but also increases safety with new, dedicated turn lanes at the adjacent County Road 3 and popular Betty’s Pies restaurant.

The Minnesota Department of Transportation (MnDOT) awarded Northland the project’s low-bid contract in August 2021. In September 2021, Northland started a small scope of work at Silver Creek. As part of creating a temporary bypass that pushed Highway 61 toward Lake Superior to make room for building the new bridge in the spring, crews installed a temporary earth retention system.

“That included a couple hundred feet of sheet pile on the lake side of Highway 61, tied back to another set of sheets on the inland side so we could retain the road and excavate for the new bridge over the existing box culvert,” said Jon Carlson, Northland’s Project Manager.

Before wrapping up the season’s work in November 2021, “We had to stack material and create a surcharge with enough weight to get the existing ground to settle before we put the new road base and new alignment on it [in 2022],” Carlson said. “We brought in some off-road dump trucks to move and stack close to 25,000 yards of material.”

The dirt originated about 600 feet south of the existing Silver Creek bridge. “There was a hill we needed to excavate out then create new slopes to make room for the new alignment, so we utilized that material for the surcharge,” Carlson said. “It was a convenient option for bringing in all that material.”

Northland restarted work at Silver Creek in May 2022, constructing the new bridge and the north side of the highway. In 2023, they’ll reconstruct the remaining portion of Highway 61 and remove the old box culvert.

At Stewart River, crews built the new bridge and the parallel highway leading to it during the 2022 construction season. In 2023, they’ll rehabilitate the historic bridge and reconstruct the existing highway.

Due to the depth of frost along Lake Superior – requiring weight restrictions lasting into the spring to prevent damage to pavement and gravel surfaces – as well as lake storms in the fall, construction seasons remain limited. Northland finished work in 2022 before the fall storms. Next year, Carlson expects to reach substantial completion at Silver Creek and Stewart River by early October, with some minor work possibly wrapping up in spring 2024.

In spring 2022, Northland’s subcontractor – Dyno Nobel, headquartered in Cottonwood Heights, Utah – performed blasting work to create space for the new Highway 61 alignments.

“For the most part it’s bluestone; this area is known for having some of the hardest rock in the nation,” Carlson said. “The blasts were 6 to 8 feet deep and covered the size of two football fields.”

However, with the work occurring as close as 400 feet from residential and business structures, crews used smaller blasts of 350 cubic yards per blast.

Northland repurposes rock from the blasting in multiple ways, including temporary and permanent stabilization that prevents construction site runoff from reaching Silver Creek and Stewart River. MnDOT also specified a heavy-duty silt trap to protect the water.

“Essentially, it’s a jersey barrier wrapped in geotextile fabric,” said Sam Anderson, P.E., MnDOT’s Project Engineer. “We placed those temporary barriers along Silver Creek, and they worked very well to keep sediment out of the creek. They’re more durable and require less maintenance than a traditional silt fence.”

In addition, “Northland did a good job staging their construction so they could stabilize areas before moving onto the next one,” Anderson said. “Any runoff went through the stabilized areas instead of open dirt.”

Along with the measures that protect water quality, the project includes restoring Silver Creek’s natural environment with a new stream bed and sides under the bridge.

Because the original box culvert construction predated MnDOT’s aquatic habitat efforts, “The driver of the stream restoration is to improve the health of Silver Creek, which is a designated trout stream,” Anderson said.

The Minnesota Department of Natural Resources (DNR) provided detailed plans for the work.

“It involves a full, 7-foot cut with random rip rap sides placed back anywhere from 12 to 36 inches,” Carlson said. “There’s also very detailed information on the sizing, location, and elevation for specific boulders to create rock ripples in the stream. Those ripples give fish the ability to rest before heading upstream to spawn.”

The earlier blasting work contributed boulders and material for the rip rap. “Our goal is to generate enough rock onsite from the blasting and the excavation that will happen next year to salvage and use everything onsite,” Carlson said.

As crews worked on the new bridges in 2022, Northland’s subcontractor, PCiRoads of St. Michael, Minnesota, conducted analyses to develop the concrete mix for restoration of the historic Stewart River bridge in 2023.

“They’re utilizing petrographic analysis of the stones and aggregate on the existing bridge, as well as color rating analysis to match the existing concrete,” Anderson said.

That process differs from MnDOT’s previous historic bridge rehabilitation. “We’re trying to obtain the color match to the existing bridge using aggregate and cementitious materials as opposed to concrete stain on the surface,” Anderson explained.

For the new bridges at both locations, Northland used single-span concrete beams with concrete decks. The concrete included a structural fiber, and rebar added reinforcement throughout the deck and rails.

At Stewart River, the new inland bridge will carry Highway 61’s southbound lane with a dedicated right-turn lane to Betty’s Pies. The rehabilitated historic bridge will carry the northbound lane, with an 8-foot pedestrian/bicycle trail.

The new Silver Creek bridge includes two 12-foot lanes, the same as the old box culvert, but adds a 12-foot trail.

“There’s a trail that runs in pieces along the north shore called the Gitchi-Gami Trail,” Anderson said. “This segment on the bridge doesn’t hook up to anything yet but will be there when the DNR makes the connection.”

• Owner – Minnesota Department of Transportation; Andrew Deming, P.E., Resident Engineer; Sam Anderson, P.E., Project Engineer
• Design Consultants – LHB, Duluth, Minn.; Isthmus Engineering, Saint Paul, Minn.
• General Contractor – Northland Constructors of Duluth, Inc.; Jon Carlson, Project Manager; Connor Houle, Assistant Project Manager; Don Renne, Bridge Superintendent; Lee Harper, Bridge Foreman; Lee Jacobs, Earthwork Superintendent; Brian Herrick, Earthwork Foreman

Photos courtesy of MnDOT