Beaufort County, North Carolina Capitalizes on the Economic Benefits of Installing Fusible PVC® Pipe

Beaufort County, North Carolina is bisected by the Pamlico River, which begins at the County seat of Washington, North Carolina. The Pamlico River is formed at Washington by the confluence of the Tar River and Tranters Creek. Several years ago the Farmville, North Carolina office of McDavid & Associates was retained by the Beaufort County Water Department to prepare documents for a waterline project known as Contract 10 Water System Improvements. A key element of the project was a 3,000 LF, 12-inch water line crossing under the Tar River to interconnect the Southside and Northside Districts of Washington. Although the Tar River crossing was the most critical horizontal directional drill (HDD) of the overall project, there were six other drill shots of varying length which were used to avoid wetlands and drainage areas.

The project was bid in 2013 with 16-inch DR9 HDPE pipe (12-inch inside diameter) specified as the product pipe for the HDD portions. The design also included several lengths of restrained ductile iron pipe on each end of the drill sections to anchor the HDPE pipe in place. Bids came in over budget, leading to a search for value engineering solutions to bring the project within budget. Hatchell Concrete, the low bidder, suggested to McDavid & Associates that 12-inch Fusible PVC® pipe would provide equivalent hydraulic performance in the application and produce savings for the owner. The HDD sections of the project were subsequently changed from 16-inch HDPE pipe to 12-inch DR18 Fusible PVC® pipe. The change in pipe material produced installed cost savings for each of the HDD segments, including in savings in excess of $300,000 on the 3,000 LF Tar River crossing.

Another post bid design change resulted in replacing the restrained ductile iron pipe connections with Fusible PVC® pipe at each end of the HDD bores. Although PVC pipe is not a soft, rubbery material like HDPE pipe, some designers will still require a modest restrained anchor to guard against separation of any of the first several segments of open cut, unrestrained, gasketed pipe. McDavid & Associates once again demonstrated that a designer with an open mind often best serves their clients' interests.

In October 2014 Underground Solutions mobilized to fuse 12-inch DR18 Fusible PVC® pipe for the Tar River crossing, supported by Rcom, Inc. and Hatchell Concrete. It took eight working days to fuse the 3,000 LF pipe string, followed by a low pressure air test of 5 psi to verify joint integrity and to confirm there was no damage to the fused pipe string from vandalism or other external sources. After a short weather delay, the leading end of the pipe string, which weighed about 100,000 pounds, was positioned into a tail ditch that had both horizontal and vertical angles to negotiate. The pipe was pulled back over a 12 hour period in early December. It was pressure tested a week later and was connected to the open cut installation in January of 2015.

The blue line represents final alignment of the HDD bore. The yellow dashed line represents the above ground pipe layout alignment. Note the 35-degree angle between the two that required attention to generate the proper entry pit in both horizontal and vertical planes. Hatchell Concrete, Rcom, McDavid & Associates, and Underground Solutions worked together to accomplish this challenging task.

The end result of proper preparation: the tail ditch was well defined for the compound curve required by the alignment issues noted in the box above. The tail ditch also served to collect the slurry returns pumped from the drill rig through the drill rods to the downhole tooling.

The prime contractor Hatchell Concrete of Manteo, NC, installed 28,000 LF of 12-inch bell & spigot PVC pipe by direct bury. Hatchell subcontracted with Rcom, Inc. of Benson, NC to perform the horizontal directional drilling sections of the project. In total, Hatchell and Rcom installed over 6,500 LF of 12-inch DR18 Fusible PVC® pipe. The system was hydrostatically tested to 200 psi and was placed into service in June of 2015.