Engineered Solutions: Tricky Feedmill Site Requires Stormwater Conveyance System
By Bart Hartsfeld and Chris M. Ross, P.E.
After acquiring Durbin Farms, Mar-Jac Poultry Alabama LLC planned a major expansion to build a new $25 million feedmill in Franklin County, Ala., that would efficiently provide feed to poultry growers in the region. Unfortunately, potential project sites with rail access and acreage for a substantial rail loop accommodating up to 100 rail cars were not readily available. Following much study and careful consideration, CDG Engineers selected the Spruce Pine site, which came with a few engineering challenges.
The proposed loop needed to cross Spring Cliff Branch, which features nearly 100-foot canyon walls and some near-vertical faces, substantially constraining site-design options. In addition, the best feedmill location needed to be lowered approximately 30 feet to match the existing Norfolk Southern rail elevation.
The initial (and most obvious) solution was a bridge to cross the gorge, but Mar-Jac was wary of this option. In addition, the project’s earthwork would produce more than 200,000 cubic yards of soil to be removed from the mill site, so CDG focused on piping and fill for the railroad crossing. The anticipated height of cover over any piping or culvert solution would be more than 80 feet, and it seemed inevitable that a cast-in-place, structurally designed culvert would be required, which would substantially impact construction time and overall cost.
Eighty feet of cover exceeded allowable limits on all design charts for typical concrete, corrugated metal and precast concrete box culverts. The time required for design and construction of this option proved prohibitive to the overall project schedule, because soil removal needed to begin as soon as possible, and that material would be needed to place over the culvert.
Based on the results of several meetings, CDG Engineers included a requirement that the selected bidder utilize the plan, profile and hydraulic capacity provided by CDG to propose a stormwater conveyance that would meet project requirements within a short timeframe.
The bid was awarded to contractor W.S. Newell, which, along with pipe manufacturer Contech Engineered Solutions LLC, proposed a polymer-coated Smooth Cor double-wall corrugated steel pipe system with a specialized bedding configuration that would provide the strength and durability needed to withstand the significant loading.
Smooth Cor’s double-wall pipe consists of a standard corrugated steel pipe as its structural exterior shell and a hydraulically smooth steel liner, providing an alternative to reinforced concrete pipe in weak soils and steep slopes. The liner is continuously attached to the exterior shell along the lock seam, and the interior liner and exterior shell are coated with polymer. The smooth steel liner provides enhanced hydraulics with a Manning’s “n” capable of 0.012.
Within a few weeks, the crossing was cleared, and the pipe was onsite. Construction wasn’t delayed, and the project schedule was held intact.
Mar-Jac Feedmill Expansion
Owner: Mar-Jac Poultry Alabama LLC
Engineer: CDG Engineers
Contractor: W.S. Newell
Product: Smooth Cor double wall CSP, 12 GA polymer-coated outer shell w/18 GA smooth, polymer-coated liner
Length: 335 linear feet
Diameter: 72-inch and 84-inch
Installation: Spring 2016