Design and construction
Learn more about the design and construction elements of the St. Croix Crossing project. Choose from the following table of contents, and stop back often. We will continually update this information and explain more activities as construction progresses.
The Loop Trail is a 4.7-mile bicycle and pedestrian trail that is part of the St. Croix Crossing project. When the new St. Croix Crossing is complete as planned in 2016, vehicle traffic will be re-routed onto the new bridge and the existing Stillwater Lift Bridge will be converted to a bicycle and pedestrian facility. The Loop Trail will cross the St. Croix River at the Stillwater Lift Bridge and on the new St. Croix Crossing bridge. Trails in Minnesota and Wisconsin will complete the loop and will connect to regional and local trail systems. Please note that the Lift Bridge will still need to accommodate boat navigation with lifts.
The Loop Trail consists of a number of segments that will be completed by 2017. The main portion of the Minnesota Loop Trail will be constructed in 2016, with final connections made in 2017. Construction of the Wisconsin portion of the project will occur in 2017.
See what the completed Loop Trail will look like:
Extradosed bridge overview:
Examples of extradosed bridges from around the world:
- Connecticut's I-94 Pearl Harbor Memorial Bridge, New Haven
- Vancouver's North Arm Bridge
- Japan's Twinkle Kisogawa Bridge
Read more about the project background, including summary of work, bidding and contracting info and more.
A closer look at the casting and installation process:
The new St. Croix Crossing will be made up of about 1,000 pre-cast segments, which will become the bridge driving surface. In order to construct these segments, crews identified two casting yards:
- Grey Cloud Island near Cottage Grove
- About 650 segments constructed here for main river bridge
- Average size of each segment is 48 ft. wide x 18 ft. tall x 10 ft. deep
- Average weight of each segment is 180 tons
- On-site near the Hwy 36/95 interchange
- About 350 segments constructed here for approach/ramp bridges
- These segments are smaller than the river bridge segments and vary in weight from 95 to 100 tons
- Crews plan to construct about one segment per day at each casting yard.
- Each segment is built in a form.
- The segments are cast in the order that they will be placed on the bridge – each segment is one-of-a-kind, like a puzzle piece.
- Construction workers set up the form and fill it with steel reinforcement bar, or rebar. This acts like a skeleton for the segment. They also place hollow plastic ducts inside the forms to make space for post-tensioned steel strands to be installed later.
- Then crews pour concrete inside the form over the rebar and ducts and wait for the concrete to cure. The concrete must meet a certain strength before crews can remove the form.
- Finally, workers transport the segment to another area in the casting year where the concrete continues to age and strengthen.
Installing the segments
When an individual segment is ready to be installed, crews transport it to the bridge site in one of two ways:
- By barge, down the Mississippi River and up the St. Croix River to the river bridge.
- By truck, from the on-site casting yard to the approach/ramp bridges.
Crews place the segments starting from a pier and working their way outward to the center of each bridge span. Cranes lift each segment into place. Then crews coat the edges with epoxy and bring the segment into contact with the previously placed segment. Finally, crews install steel strands through the hollow plastic ducts, pull the strands tight and anchor the segment into place.
Portions of the bridge driving surface will be made of cast-in-place box-shaped sections instead of pre-cast segments (see purple on map). Construction crews will pour wet concrete into forms at the bridge site. In contrast, the pre-cast segments are constructed off site and either trucked or barged in for placement. The cast-in-place process requires falsework, which is a series of temporary structures that support the bridge spans during construction until the bridge can support itself. The falsework is not a permanent part of the bridge.
Need more information to better understand the construction process? See our glossary of bridge construction terms (PDF 0.5 MB) and check out our step-by-step guide to casting the bridge approach spans segments (PDF 1 MB).
All of the bridge foundations/footings below the water surface were completed in 2013. There are two concrete footings at each of the five piers in the water. At the end of 2013, they raised up about 15 ft. above the water level. Today, they are much higher.
- 2013 Pier Foundations By the Numbers (PDF 6 MB)
This is how crews constructed everything under the water surface:
- Construction maps - Minnesota Hwy 36/95 approach work maps and full project construction map
The approach work on WIS 64 began in 2014 and be complete in fall 2016 when the new St. Croix Crossing opens. In 2014, crews will grade the new WIS 64 road surface between the river bluff and County Road E. They also constructed the WIS 35 overpass over WIS 64. Visit the Wisconsin project site for more information.
Minnesota approach work includes:
- Reconstruct and realign Hwy 36 and Hwy 95
- Directly connect Hwy 36 and Hwy 95 with ramps and traffic signals
- Add turn lanes at Osgood and Greeley/Oakgreen intersections
- Realign the Hwy 36 intersection at Greeley/Oakgreen
- Create a shared center turn lane on the north and south frontage roads
- Add a trail along the South Frontage Road to connect to the new Loop Trail
- Add ponds to improve storm water runoff and water quality
- Extend the South Frontage Road to Stagecoach Trail
- Reconstruct the Beach Road bridge
- Add traffic signals, lighting, signing and pavement markings
- Implementing new Intelligent Transportation System that includes cameras and traffic detection
- Relocate utilities