St. Croix Crossing aerial view

St. Croix Crossing

Connecting Oak Park Heights, Minn. and St. Joseph, Wis.

St Croix Crossing logo

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.

Design

Construction

Loop Trail

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

Extradosed bridge overview:

Examples of extradosed bridges from around the world:

Project background

Read more about the project background, including summary of work, bidding and contracting info and more.

Bridge deck

The bridge deck for the new St. Croix Crossing is constructed in several stages:

  1. Crossbeam construction
  2. Pier table construction
  3. Driving surface construction
SCC segments
St. Croix Crossing bridge deck construction. Click image for larger PDF version.
Crossbeam

A crossbeam is a horizontal structure that connects an upstream pier column to a nearby downstream pier column. The new river crossing will be made up of five crossbeams, one at each pier location. The pre-cast concrete segments, which make up the driving surface, frame into each crossbeam and carry all of the bridge superstructure load back to the piers.

View from above of the Pier 8 crossbeam under construction.
bridge deck

Construction process:

  • Crews install a temporary truss system to support construction efforts
  • Forms are fitted in the shape of the crossbeam
  • Iron workers place steel reinforcement bar and post-tensioning tendons (see glossary of bridge construction terms (PDF 0.5 MB)) by hand within the forms
  • Crews pour wet concrete on site into the forms and over the rebar and tendons
    • These steps are repeated three times – because of the size and detail of each crossbeam, they are constructed in three stages
  • Crews remove the forms once the concrete has cured to its desired strength
  • The steel bars and strands inside the structure are tensioned, or pulled like a rubber band, in both directions of the crossbeam

Quick facts:

  • Each crossbeam is 18.2 ft. tall, 15.2 ft. wide and 116.4 ft. long
  • The total rebar in each crossbeam weighs 478,000 lbs.
  • The total concrete in each crossbeam weighs 5,273,000 lbs. – that’s 130 truckloads!
Pier table

Constructing the pier table is the next linear step in the bridge deck construction process. Think of the pier table like a tabletop. Together with the crossbeam, it forms a large, flat surface above the pier columns. The top of the pier table will become the actual driving surface.

View of the Pier 8 pier table under construction. The pier table is poured on-site in the shape of a segment.
pier 8

Construction process:

  • Pier table construction uses a cast-in-place design
  • Forms are fitted on each side of the crossbeam in the shape of a segment (see photo). Each side is 15 feet wide
  • Iron workers place steel reinforcement bar and post-tensioning (see glossary of bridge construction terms (PDF 0.5 MB)) tendons by hand within the forms
  • Crews pour wet concrete on site into the forms and over the rebar and tendons
    • This process is repeated several times to construct the bottom, top and side walls of the pier table – the structure has hollow space in its center, similar to the pre-cast segments that are made off-site
  • Crews remove the forms once the concrete has cured to its desired strength
Driving surface

The driving surface of the new river crossing and its approach ramps will be constructed in two ways, using both pre-cast segments and a cast-in-place approach.

Pre-cast segments
The new St. Croix Crossing will be made up of about 1,000 pre-cast segments. The segments are produced off-site at two casting yards:

About 330 pre-cast concrete segments made at the on-site casting yard will become the driving surface for the bridge approach spans in Minn.
Aerial view of pre-cast concrete segments
  • 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 330 segments constructed here for approach/ramp bridges on Minn. land
    • These segments are smaller than the river bridge segments. Average size of each segment is 43 ft. wide x 10-14 ft. tall x 10 ft. deep
    • Segments vary in weight from 95 to 100 tons

Read more about the casting and installation processes.

Cast-in-place sections
Portions of the bridge driving surface will be made up of cast-in-place box-shaped sections instead of pre-cast segments (see purple on above map).

Construction process:

  • First, falsework goes up. Falsework 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
  • Forms are installed in the shape of a very long segment—this length varies depending on the approach span under construction
  • Iron workers place steel reinforcement bar and post-tensioning tendons (see glossary of bridge construction terms (PDF 0.5 MB)) by hand within the forms
  • Crews pour wet concrete over the rebar
    • These steps are repeated several times to construct the bottom, top and side walls of the structure
  • Crews remove the forms once the concrete has cured to its desired strength
Crews install falsework between Piers 5 and 7 that will carry Hwy 36 traffic and ramps onto the new river spans.
SCC segments
A close-up view of crews installing rebar within a cast-in-place form for a section of the bridge approach spans in Minn.
Rebar

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).

Bridge foundations

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.

This is how crews constructed everything under the water surface:

2013 pier foundations work. Click for larger PDF version.
St. Croix Crossing founcations work

 

Construction maps

  • Construction maps - Minnesota Hwy 36/95 approach work maps and full project construction map

Wisconsin approach

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

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