- ENGINEERING INFO
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When South Carolina DOT decided to replace two bridges leading to Folly Beach, officials notified the local utilities that their pipelines and conduits would not be allowed to be suspended from the new bridges. The existing bridges spanning Folly Creek and Folly River held gas mains, communication conduits, and a force main that would all need to be replaced and relocated under the waterways via HDD. The City of Folly Beach chose BP Barber (now URS Corporation) to begin investigations and design the crossing for the City's 8-inch force main. Soon thereafter, AT&T and South Carolina Electric and Gas (SCE&G) inquired about a joint project to install their lines, consisting of three 4-inch conduits and a 6-inch steel gas main, respectively. Eric Traenkner, Project Manager for URS, commented on the complexity of that coordination effort: "We had primary responsibility to the City of Folly Beach, but were involved in drafting agreements on design, inspection, and cost sharing between the three entities. URS designed a bundled HDD with all five pipes in a single pull, which was the easy part - negotiating the cost to share labor and equipment on a pro-rated basis, yet allow for material separately, was challenging."
Due to the length of the Folly River Crossing (over 2,800 LF), the choice of material for AT&T's 4-inch conduit became critical. Typical material for small conduit, such as jointed PVC or fused HDPE, had drawbacks in strength and elasticity that rendered them too risky to specify on such a long installation. In the final analysis, URS chose Fusible PVC® pipe for both the 8-inch force main and the 4-inch conduits, while SCE&G supplied its own 6-inch steel gas pipe. Traenkner says, "Distributing the load from pullback over the five pipes evenly was critical to success, however we knew that there would likely be some times when those loads were off-centered. Fusible PVC® pipe provided the strength and stiffness required for pullback and post-installation procedures, while minimizing the size of the borehole to deliver a cost effective installation."
The successful contractor, Chandler Construction, awarded the HDD subcontract to Environmental Crossings, Inc., and work began in February of 2012. Chandler purchased the 8-inch and 4-inch Fusible PVC® pipe and supported Underground Solutions, Inc. (UGSI) during fusion for both diameters and with internal de-beading operations for the conduit. In all, UGSI and Chandler fused and de-beaded nearly four hundred 4-inch joints. As a quality control measure, each 4-inch joint passed a mandrel test immediately following internal de-beading to ensure AT&T of a true 4-inch inside diameter. Ricky Holley, Project Manager for Chandler, says of the de-beading and mandrel testing: "In order to keep up production, Chandler forces were enlisted to de-bead each joint and run a mandrel up the length of the 40-foot pipe to prove the ID. Due to close coordination and an excellent working relationship, there were times when UGSI and Chandler were able to fuse and de-bead 1600 feet of 4-inch in a days' time."