St. Croix bridge segments taking shape

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By Brian Johnson
Dolan Media Newswires

While workers make progress on the future St. Croix River bridge at the project site near Oak Park Heights, Minn., other construction activities are occurring about 30 miles away — on a different river.

In a spacious yard at Grey Cloud Island in Minnesota, crews are casting 650 180-ton concrete segments that will eventually ride on a river barge to the project site, where they will form the driving surface for the new bridge between Oak Park Heights and St. Joseph, Wis.

A second casting yard is set up just north of Highway 36 and west of Highway 95, where workers are creating 330 precast concrete segments that will become part of the decks for the approach bridges over land.

It’s all part of the $626 million St. Croix Crossing project, which includes the new mile-long river bridge, approach work on both sides of the river, and conversion of the historic Stillwater Lift Bridge to a pedestrian and bicycle span.

The project is on schedule, with the new bridge is expected to start carrying traffic in fall 2016, according to the Minnesota Department of Transportation.

MnDOT representatives gave media members a tour of the Grey Cloud Island casting yard Tuesday.

At the site, accessible only by a gravel road, crews of carpenters, ironworkers and quality control experts, clad in yellow safety vests and orange hard hats, carefully crafted the giant concrete puzzle pieces that will go into the bridge.

The segments will be installed beginning in May, said Michael Beer, MnDOT’s St. Croix Crossing project manager. By mid-summer, as more segments go in, the structure will begin to resemble an actual bridge.

“It will really start to look more exciting than just piers sticking up out of the water,” he said.

Of the 650 segments that will be produced at Grey Cloud Island, 105 have already been completed. The other casting has produced about 61 segments so far.

Grey Cloud Island, near Cottage Grove, Minn., is an ideal location for the casting work because there’s a lot of room, easy access to aggregate, and a climate-controlled building about the size of two football fields, MnDOT representatives say.

The Lunda Construction-Ames joint venture, which has the $332 million superstructure contract for the project, is leasing the property from Aggregate Industries, a producer of aggregate-based construction materials.

“The concrete is able to be produced right here with the aggregate,” said Paul Kivisto, MnDOT’s bridge construction engineer for the project, who spoke to reporters while standing in front of one of the finished concrete forms. “And along with the space for construction and the barge facility … to get them up to the river — all make it a very convenient place for construction.”

About 80 workers are at the Grey Cloud site. In all, it takes about 250 to 300 work hours to construct each segment. Workers are cranking out six to eight of those segments every week. Each segment contains about 80,000 cubic yards of concrete and about 72,000 pounds of steel. They’re 48-feet wide, 18-feet tall and 10-feet deep.

At Grey Cloud Island, crews construct steel rebar “cages” that act like a skeleton for each segment, and use a crane to place the cage inside an adjustable form, according to MnDOT.

After installing hollow plastic ducts that allow space for post-tensioned steel strands, which will connect the segments together, workers pour concrete inside the form. Before and after each pour, surveyors measure the segments to precise specifications.

“We survey to the nearest one-thousandth of a foot,” Kivisto said.

Segment “lifters” capable of hoisting 220 tons transport the finished segments to outside storage areas, where the concrete continues to strengthen and the segments await the river barge journey to the project site.

The segments are shuttled to a river barge docked on the Mississippi River, about one-fourth of a mile from the casting yard. After a short distance down the Mississippi River, the barge turns into the St. Croix River and completes its journey to the project site.

Major contractors on the job include Black River Falls-based Lunda Construction and Burnsville-based Ames Construction (superstructure); Ames and Lunda (Minnesota approach work); and Plain-based Edward Kraemer & Sons (river foundations).

Still to be awarded are contracts for some of the approach work on the Wisconsin side of the river, a loop trail, and conversion of the historic lift bridge.

All in all, the project has gone well so far, Beer said.

“No project has zero challenges,” he said. “This one has been big and has had its share of them. But we have been working through them. So things are where we want them to be for it to be opened up for fall of 2016 traffic.”