Did You Know...

Concrete Is Placed Year Round

Concrete placing has been ongoing throughout the chilly winter months as crews have been working to construct the capitals and caps for the new Pierre-Fort Pierre Bridge. When temperatures dip, crews insulate the forms with concrete blankets during the forming process. They also heat the insides of the forms until the point when they place concrete. The concrete generates heat as it cures, and the blankets around the forms act as insulation holding in the heat. Hot water is also used in the concrete mix to bring the entire mixture’s initial temperature above 50 degrees.

Concrete placing for a capital.
Form Liners Used to Create Quarry Stone Pattern

Form liners are being used to provide an aesthetically pleasing appearance to the concrete abutments of the new bridge. They are placed on the inside of a concrete forming system before the concrete is placed and act as a mold for the concrete. Once the concrete has set, the form liners are removed from the hardened concrete surface, and the concrete surface is permanently textured with the pattern of the form liner. The form liners for the new bridge will create a quarry stone pattern, and the texture finish color once finished will be silver.

Photo of Pierre-side abutment.
Pedestrian Fence Railing Will Contain Stars

The black steel pedestrian fence railing for the new Pierre-Fort Pierre Bridge will contain a star motif between the intermediate and top rails. Design plans for the new bridge call for a total of 263, 12-inch decorative rail steel stars. The patriotic railing was the preferred railing design picked by the public. It will complement the classical two-column pier and rounds out a federalist style for the bridge.

Star mockup for pedestrian fence railing.
Bridge Construction 101

Many terms are used in explaining the construction of a bridge—abutments, capitals, caps, bents, etc. As we see components for the new Pierre-Fort Pierre Bridge visibly taking shape, here is a bridge construction 101 refresher.

The main components of a bridge are the foundation, substructure, and superstructure. These core areas have other parts within them. For the new Pierre-Fort Pierre Bridge, 12 drilled shafts have been constructed as part of the foundation. The substructure includes the bents and abutments, while the superstructure includes the girders, bearings, and deck.

Bridge bent graphic.

An abutment is a component of a bridge that connects it to the approach roadway and provides vertical support to the bridge superstructure at its end. The abutments also function as retention walls for the ground. The Pierre-side abutment is abutment eight, and the Fort Pierre-side abutment is abutment one.

Six bridge bents will make up the substructure of the new bridge. The six bents will support the superstructure and distribute bridge load to the underground shaft foundation. First, the columns are constructed on top of the drilled shafts. Next, the capitals are constructed on top of the columns. And finally, a cap connects two adjacent capitals to form a bridge bent.

The next step is the superstructure and erection of the structural steel girders. Girders are also referred to as beams, and they give support to the bridge deck, or surface that will be the roadway.

Drilled Shafts Installed Under Water

*To help explain the process of the drilled shaft installation, the first minute of this video is shared in order to visually represent the plan Jensen Construction and SDDOT approved for this project. The video was created by Kalloc Tech.

An oversized steel casing, 13.5 feet in diameter, was installed from a floating barge down through the water into the river bottom. A permanent 10-foot diameter steel casing was installed inside the oversized casing and allowed for the concrete to be placed inside the 10-foot casing without the need to worry about fresh concrete being spilled into the river. 

The permanent casings were approximately 49 feet long. They were installed into the bed of the river and turned into the shale, creating a solid foundation. 

The “shaft” was then excavated using an auger to drill deep into the shale below the river’s bottom.  This occurred in a two-step auguring process. Once the “shaft” was excavated and cleaned out, the steel reinforcing (rebar) was inserted into the drilled shaft. They are typically referred to as “cages” as can be seen on the video. 

The cages were fabricated offshore and taken by barge and lowered into the drilled shaft using a crane on the barge. Special spacers were used to make sure the rebar did not come into contact with the bottom or sides of the drilled shaft to ensure that the rebar was completely encased by the concrete. 

Upon final inspection of the placement of the rebar, concrete was then placed in the drilled shaft. A concrete pump was used to fill the drilled shafts with concrete.  This was done by displacing the water in the drilled shaft with concrete using a device called a tremie tube. A tremie tube is a long pipe with a length greater than the depth of the drilled shaft.

One end of the tremie was lowered to the bottom of the drilled shaft, and concrete was placed through the use of the tremie tube. Before starting to place the concrete, a foam ball was inserted into the top end of the tremie tube. Once the ball was in place, concrete was placed in the tremie tube above the ball. By the weight of the concrete on top of the ball, the ball was pushed down the tremie tube which acted as a squeegee pushing the water down and out the bottom of the tremie.

When the ball exited the tremie’s bottom, the concrete then quickly began to displace the water in the bottom of the shaft in an upward direction. The tremie remained embedded into the concrete by five feet or more and was lifted at the same rate that the concrete came up in the shaft until the tremie reached the top of the permanent casing.  

Numerous testing procedures were used throughout this process to ensure the highest quality in the materials used and to ensure the installation was correct. Of additional note, each drilled shaft contains approximately 365 cubic yards of concrete and nearly 65,000 pounds of steel. The concrete obtained a strength in excess of 4,500 pounds per square inch.