19.5 Foot (5.9 Meter) Tall Gravity Wall Creates Access For FBI Headquarters
Year Built: 2011
Goal: Overcome Extremely Tight Parameters & Significant Grades
Project Duration: 25 days
Project Magnitude: 8000 square ft.
Height: 19.5 ft.
Gravity Retaining Wall Blocks - Massive, one-ton Redi-Rock gravity blocks rely on the sheer mass of each block to hold back the earth.
This case study is also featured on Redi-Rock.com.
The Federal Bureau of Investigation is relocating its division headquarters from downtown Cincinnati to a high-profile site adjacent to Interstate 71 and planned mixed-use development in Sycamore Township, Ohio. In order to accommodate the anticipated level of employees and visitors to the site for the new FBI building and other planned development, the township needed to provide new access. A new public access drive was designed from Hosbrook Road to the development sites.
The new roadway is located between existing residential neighborhoods and a major office building. The terrain along the new access road included some significant topographic challenges. In order to minimize the earthwork and impacts to the existing wooded buffer between the adjacent residential neighborhoods and the development, it was decided to construct a 19.5 ft. high, 700-ft. long retaining wall along the south side of the new roadway.
After evaluating the costs and impacts of a variety of wall systems including conventional cast in place cantilever walls, drilled soldier pile walls to conventional segmental walls with geogrid reinforcing, URS contacted Redi-Rock to explore the potential use of its large block retaining wall system. Following close coordination between URS, Redi-Rock and the township, it was determined that the Redi-Rock system could meet the goals of the project better than the other system.
“Sycamore Township chose Redi-Rock because we had a limited amount of space; we did not want to cut back behind the wall for tie-ins and we didn’t want to lose trees that were buffering the neighbors from the project,” explained Tracy Kellums, Superintendent for Sycamore Township.
Dave Wormald, P.E. of URS Corp. explained further: “One of the primary reasons we chose the Redi-Rock system was because we wanted to design a gravity wall to reduce the amount of excavation required with minimal disruption behind the wall as well as creating an aesthetically pleasing appearance.”
It’s no secret that Redi-Rock is known for building tall gravity walls using massive, one-ton blocks to get the job done. But this 19.5 ft. tall wall gave engineers the chance to show just what Redi-Rock blocks are really capable of.
To reach the required 19.5 feet with a gravity wall, URS utilized several unique components of the Redi-Rock system to achieve a custom solution for the project without the need for geogrid reinforcement or anchors. URS utilized the Redi-Rock propriety analysis software to evaluate a variety of wall cross sections to arrive at the hybrid design for the finished wall.
First, URS specified 3420-pound Redi-Rock 60 In. base blocks for the bottom six to eight courses of the wall. Just one course was buried. Then, URS specified several courses of 9 In. setback blocks throughout the wall to vary the batter. “We incorporated the 9 In. setback blocks to increase the resistance to overturning forces without the need for geogrid reinforcement,” Wormald explained.
For the higher courses in the wall where the loading was less, the blocks transitioned to 41 In. Series blocks and 28 In. Series blocks to achieve the full height of the wall. Compacted free-draining aggregate backfill and leveling pads were used. Ornamental fencing—matching fencing used by the township for nearby streetscapes—was mounted at the top of the wall.
Combining a variety of Redi-Rock blocks allowed the wall to achieve its goal height while minimizing excavation and impact on the trees. Plus, the gravity solution saved the township time and money on installation.
An additional benefit was the superior aesthetics the system offered. “We chose the Ledgestone texture because we felt it looked the most like real rock to match up with other retaining walls that we have throughout the township,” Kellums explained.
Redi-Rock is the only large block retaining wall system on the market that offers Ledgestone, a texture and color combination so natural, it’s hard to distinguish from natural stone. “Aesthetically, it looks really great,” URS noted.
In the past several years, the township had erected several conventional concrete retaining walls faced with stone veneer. These walls were located within a half mile of the site, and the township wanted the walls on the access road to match the appearance of the other smaller walls in the area. Ornamental, matching fencing used by the township for nearby streetscapes was mounted at the top of the wall to reinforce the urban design context of the area.