The first major target has been reached in building a new St. Croix River bridge.

All 40 caissons, also known as drilled shafts, that will support foundations for the bridge are complete and filled with concrete, the Minnesota Department of Transportation (MnDOT) said Friday.

Caissons are steel casings 9 feet in diameter that extend 90-120 feet below the river’s surface into bedrock, anchoring massive foundations much as legs support a stool.

Also, 40 percent of footings and columns — other segments of foundations that hold the four-lane bridge in place — were filled with concrete. All foundation work will be finished by early 2014, MnDOT said.

The overall bridge project, costing up to $675 million, includes new approach highways in Oak Park Heights and St. Joseph Township, Wis. Minnesota and Wisconsin will split the cost.

Additional information is available on the project website.


Kevin Giles | @stribgiles