Tensar Site Development Solutions

However, Post^® was unfamiliar with the Sierra System and initially worried about the way the finished slopes would appear. Having seen two examples of lightly landscaped Sierra Slopes in Atlanta, Post^® decided that its slopes should be heavily planted. According to Larry Meister, Vice President with Post Eastern Development, "Landscaping is a major marketing tool for Post^®. The goal is to present a clean, park-like atmosphere for residents. We wanted to make sure there would be no baskets or earth showing; we wanted a finished look."

Ultimately, Post^® selected the Sierra System recognizing the benefits of a less expensive, but still structurally sound earth retention solution that would promote a living wall of plant material. According to the contractor, Joe Harris, president of Pinnacle Design/Build, Alpharetta, GA, "The most important aspect is that the owner got an earth retention system that acted as a retaining wall while meeting the aesthetic requirements. The solution has both function and beauty."

While the "soft," green solution of the Sierra System met the project requirements, rock excavation presented a challenge in constructing the slope. Aside from the difficulty of engineering around a rock/soil mix, rock is expensive to excavate. So wherever possible, rock was left intact to reduce costs.

Through an innovative design, TET engineers were able to save both time and money by minimizing rock removal. Due to the variability of the quality of the exposed rock, field adjustments to the design were also performed by TET engineers based on their field observations.

Construction on the design/build project began in July 1997 after TET selected Pinnacle Design/Build to construct two Sierra Slopes totaling 5,000 square feet. The final design had to accommodate varying reinforcement needs throughout the slopes. The fractured, but competent rock at the base of the slopes permitted the use of shorter geogrids while the 2H:1V grade on top of one reinforced slope required substantially longer geogrid reinforcement. To deliver the long-term design strength and to assure surficial stability, TET engineers specified Tensar^® uniaxial geogrids and Tensar^® biaxial geogrids, respectively.

Using 18-inch vertical leg, welded wire basket forms which were offset 9 inches, a 15-foot high, 0.5H:1V reinforced Sierra Slope was constructed incorporating a wrapped face and non-biodegradable erosion blanket. The flexibility of the facing system also permitted Post^® to incorporate a portion of rock ledge to enhance the natural appearance of the excavation by wrapping the steepened slopes back into the ledge.

To further improve surficial stability, erosion control materials were carefully matched to the site-specific conditions. Although a number of facing treatments can be adopted, including sod, bioengineering, erosion blanket and hydroseeding, the Post Landscaping Division opted to plant the slope with a combination of junipers, winter jasmine, abelia, and other low-maintenance, attractive, rapidly-growing ground covers.

The combination of spreading forms and weeping forms was selected to assure maximum coverage while creating an interesting environment of texture and color. Post^® also employed a drip irrigation system with nozzles placed on the 2-foot plant centers. Because Post^®typically employs 3H:1V slopes, the narrow terraces presented a challenge. Kleinhelter noted that the actual planting took longer than originally anticipated, primarily due to cutting through the geogrid and erosion control blanket. But he said, "Definitely we’ll use it again. It’s a lot better looking than a segmental retaining wall."