Project Profile: Precast Security
Residents of Tulsa, OK, know something about severe rainstorms and the flash flooding that can accompany such events. Recently, the city and its residents came together with a plan to mitigate the costly effects of these floods and the erosion of landowners’ property and property values. A series of existing drainage channels were targeted for reinforcement.
One such project was the Fry Ditch Channel located in the southern portion of the city at East 97th Street and South Sheridan Road. On one side of the channel was an existing earthen wall that retained the waters of the Oknoname Reservoir. On the other side were a number of existing homes, with the lots extending up to the channel. While stabilization of the channel was important, it was also critical that the solution resulted in minimal disturbance or excavation of the homeowners’ property, and that it met long-term durability and design life criteria. One possible choice was the traditional cast-in-place option, but that would have required additional excavation at the base of the wall to accommodate a cantilevered footing.
The search for a solution led the project engineer, SAIC Energy, Environment & Infrastructure LLC, to select a large-scale wet-cast segmental retaining wall block to line Fry Ditch. This choice satisfied a number of important considerations. First, long-term durability of the concrete was essential. The product chosen is manufactured from a wet-cast, air-entrained concrete mix that is designed to resist the adverse effects that repeated freeze-thaw cycles have on concrete. Second, the size and mass of the individual blocks ensured the stability of the segmental wall even in flood or rapid flow conditions. The blocks used in the design of the wall weighed from 1,000 to 3,000 pounds each. Third, the product allowed the design of a wall without the need for any geogrid or other mechanical slope stabilization. This minimized excavation requirements and resulting site disturbance.
“Based on its mass and interlocking design, the large block wall system was selected, obviating the need for geogrid, which the city of Tulsa does not allow within utility easements,” says Rhonda J. Dudeck, P.E., of SAIC. “The pleasing aesthetics and versatility in the finishes available were also a favorable factor with the adjacent homeowners. Additionally, construction of the wall was less destructive and quicker than construction of a cast-in-place concrete wall.”
The actual product used on the project was the ReCon Block from ReCon Wall Systems Inc. The ReCon Block was manufactured and supplied by Arrowhead Precast LLC of Jenks, OK. The ReCon Block has a face size of 48 inches in width and 16 inches in height. Although the typical ReCon Block has a setback between courses of block of just 1 inch (resulting in 3.6 degrees of batter), the design of the Fry Ditch project utilized ReCon’s special channel block, which allows for an 8-inch setback from one course of block to the next. The resulting wall batter of 26 degrees allows for taller gravity walls. The Fry Ditch wall reached 17 feet 4 inches in height, without the use of any additional reinforcement. For the base of the wall, ReCon supplied a 60-inch-deep block weighing 3,000 pounds. As the wall was built to full height, the block depths transitioned to 45 inches, then 39 inches, and finally just 24 inches at the top of the wall.
Little did the team that put together the Fry Ditch improvement project know that the wall would be tested even before construction was completed. On July 8, 2010, the rains came to Tulsa in torrents and filled the Fry Ditch. At that time, wall had been built to full height, but final grading at the top and bottom of the wall had not been finished. The floodwaters subsided and no harm was done. The wall remained intact and construction was completed on schedule.
“The ReCon system was simple to install. Once we started the wall, we were able to stack block as fast as we could unload it,” says Ron Hensley of R.L. Hensley Construction, “and it’s a great product that stays in position even with heavy rainfall and creates a strong uniform look when complete.”
Now the homeowners along Fry Ditch can rest easy knowing that their backyards are not going to be eroded away with each recurring flood event.