In the spring of 2015, plans were prepared for a new Dollar General Store off Mississippi Hwy 19 South, just east of Meridian, Mississippi. The site plan for the new store would require an 11-foot grade separation along the south property line to allow for access to the parking lot off Sandflat Loop Road.
The geotechnical report for the project described the site soils as loose to medium dense clayey sand with marginal shear strength. In addition to the required height and close proximity to the property line, the top of the wall would be required to support a crest slope and drainage swale to effectively manage surface run-off. To add to the complexity of the retaining wall design, a drop inlet would be placed immediately behind the wall that would serve to drain the crest swale. The drop inlet structure would need to be the full height of the retaining wall with an 18-inch diameter outlet pipe that would cross under the base of the retaining wall.
Based upon these considerations, the maximum design height of the retaining wall would need to be 15 feet. With no horizontal space between the proposed wall face and the property line and the required drainage structure immediately behind the modular wall units, external reinforcement such as a geosynthetic geogrid could not be considered. A gravity wall system capable of the required design height would be the only suitable option.
When the contractor, Mike Rozier Construction of Hattiesburg, Mississippi, contacted MMC Materials in Jackson, Mississippi to inquire if the Redi-Rock retaining wall system could provide the required solution, MMC called on JC Hines and Associates to prepare preliminary designs for cost estimating. Once accurate material quantities were determined from the preliminary design, the contractor quickly concluded that the Redi-Rock design would meet the project budget requirements and JC Hines and Associates was released to prepare final construction drawings.
The final Redi-Rock wall design utilized 60-inch blocks on the bottom that transitioned to 41-inch units and finally to 28-inch block units at the top of the wall. A single course of 9-3/8” set-back blocks (in lieu of a consistent standard setback of 1-5/8”) was incorporated in the design to increase the facing batter achieving the required factors of safety for stability.
The total face area of this wall is 2,923 square feet. The natural gray Cobblestone Redi-Rock units were manufactured by MMC Materials in Jackson, Mississippi.