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How to Build Beautiful Bridge Abutments with Segmental Retaining Wall Blocks

Project Name

Gaynor Road Bridge #108

Customer Name
Clermont County

Design / Specifying Engineer
Todd Gadbury, P.E. Clermont County Bridge Engineer

Block Manufacturer
Redi-Rock Structures of OKI

Wall Installer
Clermont County

Project Location
Clermont County, Ohio

Year Built
2005

Project Scope

In the world of retaining walls, engineers are often faced with two choices: (1) specifying a structural yet unattractive wall, or (2) specifying an attractive wall that isn't structural.

When Clermont County engineers discovered that the bridge abutments supporting the Gaynor Road Bridge were deteriorating, they were forced to close the bridge. For a year and a half, the county debated solutions for reconstructing the bridge. The County needed a structural retaining wall to act as a bridge abutment, but they also wanted the solution to be attractive.

Several factors influenced the decision the county eventually came to.

First, the new bridge abutments needed to be aesthetic, as an educational nature preserve was directly adjacent to the bridge.

The nature preserve was donated to the Cincinnati Nature Center by Cincinnati native Neil McElroy, who served as president of Proctor and Gamble from 1948 to 1957 before becoming Secretary of Defense under Dwight D. Eisenhower. The year McElroy died, his 535-acre farm was donated with instructions that the farm kept as a working farm and used for “educational activities” and be “kept intact in order to preserve wooded areas, flowers and its natural beauty.” Therefore, a natural look for the bridge abutments was essential.

Second, the county was looking for a cost-effective, structural solution that would allow them to utilize their own equipment and crews.

Originally, the county considered using cast-in-place abutments, vertical piers or reinforced concrete grade beams. But since construction needed to take place in the dead of winter, the county needed a solution that wouldn’t require provisions for heating and curing.

Based on these needs, Clermont County's Bridge Engineer Todd Gadbury, P.E. chose to design the new bridge abutments using Redi-Rock retaining walls.

"I came up with the design using Redi-Rock because it was a winter project and we didn't want to pour monstrous abutments," Gadbury said. "Using Redi-Rock worked well in this application."

By using Redi-Rock's massive one-ton retaining wall blocks, the county was able to construct structural walls that could act as abutments more cost effectively than cast-in-place.

Redi-Rock's Cobblestone texture blocks are cast in molds taken from natural quarried stone. Even though each block has nearly six square feet of face, the Cobblestone texture has the appearance of six smaller blocks, which gives finished walls a more natural look as well.

Redi-Rock's unique interlocking system installs simply, using a small crew and a piece of heavy machinery such as a backhoe. The walls were installed quickly, and installing Redi-Rock did not require provisions for heating and curing as a cast-in-place wall would have. Installing the walls has a fast learning curve, which proved beneficial for the county's crew.

As construction began, the bridge deck off was lifted off the existing abutments. Since the bridge deck was still in good condition, it was set aside to be re-used. The crew removed the existing abutments, exposing a heavily eroded bank.
The county's crew excavated a five ft. deep by five ft. wide trench. At this depth, the crew reached gray shale and thinly bedded limestone bedrock. The crew then poured concrete into the trench to create a concrete leveling pad for the abutments. Gadbury specified a concrete curb at the front of the concrete leveling pad.

Like a giant Lego system, each Redi-Rock block interlocks with the one above and below it, creating a structural wall. Because the blocks were manufactured off-site by Redi-Rock of OKI, the walls did not require provisions for heating and curing, even though they were installed in the dead of winter. For these abutments, Gadbury specified Redi-Rock 41 in. (measured from face of blocks to rear) retaining wall blocks reinforced by Stratagrid geogrid extending behind the wall.

Once the walls reached the proper height, the crew constructed a reinforced concrete grade beam that bears directly on the RR blocks. On top of the grade beam, the County used two cranes to set the reinforced concrete bridge box beams directly on the concrete grade beam. There are no piers or piles or deep foundations to hold the bridge deck up; the load of the bridge rests directly on the abutments.

"Using Redi-Rock simplified construction greatly," said soil engineer Joe Kowalski, P.E. who reviewed the design for the County. "The County just built the Redi-Rock wall, put beams on it and walked away."

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