Deep Muck Raises Costs for New St. Croix River Bridge

Fri May 11, 2012 - Midwest Edition
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The St. Croix River.
The St. Croix River.

STILLWATER, Minn. (AP) The price tag for the new St. Croix River bridge could hit $676 million — almost triple the $234 million spent to replace the collapsed Interstate 35W bridge over the Mississippi River in Minneapolis.

And the main reason, according to the Minnesota Department of Transportation official in charge of both projects, is muck

Project manager Jon Chiglo told the St. Paul Pioneer Press that the deep muck at the bottom of the St. Croix means foundation work for the new bridge accounts for 40 percent of the total cost estimate.

Construction of the four-lane bridge that will link Minnesota and Wisconsin at Stillwater is slated to start next spring and end in 2016. Barges are expected to be moved to the site in late May so crews can start boring test shafts into the river for structural-load testing. That work should take two to three months.

Crews are expected to have to drill down 160 ft. (49 m) — the longest shaft drilled for the I-35W bridge was 90 ft. (27 m), Chiglo said.

“In some instances, we have 85 feet of muck in the St. Croix that we have to drill through before we reach the softer sandstone,” said Chiglo. “And then there’s 30 to 40 feet of soft sandstone that we’ll go through and, ultimately, get into that more sound bedrock that we have to go into about 30 to 40 feet.”

Another complication is that the new bridge — which will be just less than a mile long at 5,100 ft. (1,554 m) — will have six sets of piers in the water.

“The foundations for the St. Croix crossing project are extremely complex compared to the I-35W bridge,” Chiglo said.

The old I-35W Bridge over the Mississippi River in downtown Minneapolis collapsed Aug. 1, 2007, killing 13 people and injuring 145 others. The replacement opened Sept. 18, 2008.

The new St. Croix River bridge will replace the aging Stillwater Lift Bridge as the main Minnesota-Wisconsin crossing north of Interstate 94. It will divert thousands of daily commuters away from Stillwater’s historic downtown and route them instead to Minnesota Highway 36 through Oak Park Heights. The old lift bridge will be converted into a crossing for bicyclists and pedestrians.

MnDOT officials say Minnesota’s share of the project is basically fully funded; they’ll be using about $160 million in federal money and $200 million in state bond funds. Wisconsin’s share will be as much as $305 million. The Wisconsin Building Commission, chaired by Gov. Scott Walker, recently authorized the Wisconsin Department of Transportation to borrow $225 million to help fund its share. Wisconsin has now secured 80 to 90 percent of what it needs based on the current cost estimate, according to WisDOT officials.

President Barack Obama signed legislation in March that exempts the bridge from the Wild and Scenic Rivers Act, which had been an obstacle to the project.

“You know when you have 100 percent of the U.S. Senate and 80 percent of the U.S. House, and the president signs a bill that allows us to move forward, that definitely provides some momentum,” Chiglo said.

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