What is a bridge abutment?
A bridge typically consists of two main parts: the substructure and the superstructure. The bridge abutment encompasses any end support structure that connects the bridge to the approaching roadway while transferring loads to the foundation. This critical substructure component supports the ends of the bridge and the soil under the road. Additionally, substructure can refer to the piling, which transfers the bridge loads from the bridge into the piling and into the deeper layers of the soil. The substructure might also have wing walls, which retain the soil along the sides of the bridge abutment.
The Benefits of Sheet Pile Bridge Abutments
Steel sheet pile bridge abutments are an innovative solution that provides time and cost savings on many types of bridge projects. The basic concept of this solution is that the sheet piles can provide both the lateral support for the soil and the vertical support for the bridge.
Steel sheet pile bridge abutments are considered an accelerated construction method, significantly reducing the overall construction time in many cases. With a concrete abutment, temporary retaining walls (often steel sheet piles) are required to install the bearing piles. Then formwork must be built, concrete poured, and curing time allotted to enable the concrete to achieve its design strength. With a steel sheet pile solution, the sheet piles are driven and a concrete cap is placed on top of the wall to transfer the loads from the bridge to the sheet piles.
A sheet pile bridge abutment solution, does not require temporary cofferdams, allowing the abutments to be brought closer together, on stream crossings, to reduce the span length. Reduction of the span length provides overall reduction in the cost of the superstructure. Additionally, due to the small footprint of this solution, disruption of natural streams can be avoided and in-water permitting can be simplified or avoided altogether.
Another added benefit to this solution is the built-in scour protection when crossing a river or stream. With traditional concrete bridge abutment and piles, significant scour can erode the soil under the concrete abutment, undermining its integrity and requiring repairs. Steel sheet piles are driven much deeper into the soil than a concrete abutment, providing significant scour protection. Pile lengths can be specified and purchased at long lengths to meet long-term scour estimates, ensuring bridge durability.
Parts of Bridge Abutments
Abutments are complex assemblies made up of several key parts, each serving specific functional requirements. Here are the main parts and their roles in ensuring the stability and durability of bridges:
- Pile Cap: The base component of an abutment, designed to distribute the loads from the bridge into the pile.
- Abutment Wall: The visible part of the abutment that supports the end of the bridge superstructure and retains the embankment fill.
- Wing Walls: Extensions of the abutment wall that retain the embankment next to the road that approaches the bridge.
- Bearings: Mechanical components placed between the bridge superstructure and the abutment to accommodate movements and rotations of the bridge deck.
- Backwall: Located at the top of the abutment. Serves to provide a transition between the bridge deck and the embankment.
- Piles: Driven deep into the ground beneath the abutment to reach stable soil layers.
- Drainage Systems: Effective drainage systems are crucial components of bridge abutments, designed to manage water runoff from the bridge deck and surrounding areas.
Abutment construction process
There are many different construction methods for bridge abutments which utilize steel, concrete, geosynthetics, and other materials. Abutments can be integral, where the bridge and the abutment move together, or semi-integral, where the abutment and the superstructure move independently when responding to forces on the bridge. There are pros and cons to each type of bridge abutment and construction method. Review your local Department of Transportation’s guidance regarding types of bridges that are acceptable or recommended in your state.
Sheet pile bridge abutments are constructed by first installing the sheet piles for both the abutment face and the wing walls. Tie rods and a deadman wall are required in some high-load applications. Additional piling behind the sheet piles can be used if insufficient bearing and skin friction capacity cannot be obtained with the sheet piles themselves. From there, soil backfilling behind the sheet piles and construction of the concrete cap and bridge deck can proceed. As described, it’s clear to see that this solution eliminates a lot of construction stages, and therefore can eliminate a significant amount of time and show increased cost savings.
Sheet piling offerings
Nucor Skyline offers NZ, PZ, and SKZ sheet piles which are made in America and meet federal Buy America guidelines. This product range is suitable for any Department of Transportation (DOT) project you may have in design. To see some examples of how sheet piling is used for bridge abutments, please click here to visit our case studies.