The pipe will connect the Port Royal Water Reclamation Facility with the Secession Golf Course in Beaufort, S.C. This project was completed on June 12 and marked the longest single HDD crossing of thermoplastic pipe in history.
Using fusible PVC is becoming more common in the industry, and with this successful crossing, it is a feasible and economical material for HDD crossings. BJWSA had considered alternative materials, including steel pipe and HDPE, but ultimately selected fusible PVC because it combined the best elements of those alternatives. Steel pipe has adequate strength to be pulled that distance, but is costly and requires elaborate corrosion control measures. HDPE, while corrosion resistant, is limited by its strength-to-weight ratio and its elastic nature when loaded in tension for extended periods.
This length of bore was previously unheard of for fusible thermoplastic pipe. “Drilling a length of over 5,000 ft for fusible polyvinyl chloride pipe had never been done before, so we had to take many precautions to ensure the successful completion of the job,” said Mears project superintendent Edd Birdell.
BJWSA contracted with Underground Solutions Inc. (USGI) to supply its proprietary fusible PVC pipe for the job. This pipe was a key component in the successful completion of the job.
Mears used its 330,000-lb capacity rig on the entry side of the crossing and one of its 60,000-lb rigs on the exit side during pre-reaming to apply tension on the cutters. The bore reached a maximum depth of about 80 ft through sandy limestone and silty sand. According to Birdwell, about 95 percent of the drilling was through good conditions, while the remainder of the drilling was “choppier,” which made the drilling tough.
Installing fusible PVC with HDD is not yet as common as using more traditional steel or HDPE materials. Mears was careful throughout the HDD operation and especially in handling the pipe during the pullback operation. They did not exceed 67,000 lbs of pull on the pipe throughout the installation. This allowed the crew to stay well under USGI’s warranted safe pulling force of 100,000 lbs. Previously, UGSI had only seen its Fusible PVC pipe installed in drills of up to 1,480 ft. and a slipline installation of 3500 ft; however, UGSI was confident that its pipe could be successful in longer drills.
UGSI vice president Tom Marti said, “Great cooperation between Mears, BJWSA and UGSI allowed for this groundbreaking success.” Marti also noted that attention to detail and intense planning were critical to completing the job on time and with record-breaking results.
The pullback was a long process, taking 17 hours to complete. What made the pullback difficult was that, due to site constraints, the pipe could only be pre-fabricated into five, approximately 1,000-ft long, sections. This meant that every 1,000 ft, the pullback had to be halted and the next section of pipeline fused on. This was worrisome to some, as they feared that debris in the bore hole would settle and make the continuation of the pullback difficult. However, each tie-in operation was completed in about two hours without problems.
Another concern was the buoyant weight of the pipe. However, Mears had developed and implemented a ballast control system that was used when pulling the pipe back through the drilled hole. Careful consideration was given to the handling of the pipe during the entire pullback process. A tension recorder was employed in the downhole assembly to monitor actual pull force at the pipe. This assisted the driller in keeping the tension at a constant and reasonable amount.
With the completion of the project, BJWSA will deliver up to 1 million gal of reclaimed water per day to the Secession Golf Course and hopes to supply a second nearby golf course in the future. The overall project will cost $1.7 million and has taken a total of 18 months to plan and complete. Mears arrived and left the site within a month.
The BJWSA was pleased with the results that Mears was able to achieve. As much as 40 percent of the area is covered in water, which makes HDD a practical option for many projects. Final connections have been made and the pipeline is now functional.
BJWSA deputy general manager Ed Saxon said, “The project was a huge success. Many of our projects have utilized directional drilling but this was, by far, the most complicated. By utilizing a risk sharing approach which is unique in the public sector, we assembled a great team and Mears and USGI worked cooperatively to complete the drill within budget and on schedule. We could not be happier with the outcome and are currently discussing a project with Mears and UGSI to directional drill 6,300 lf of 16-in. Fusible PVC, another potential record.”
As designers and contractors discover the capabilities of Underground Solutions Fusible PVC pipe, its use will likely increase. Marti believes that there will be more and more opportunities for fusible PVC pipe in the future. It is cheaper and more flexible than traditional steel although it has less tensile strength.
“I believe that the use of fusible PVC will expand in the future because it is a nice middle ground between steel pipe and HDPE pipe,” Birdwell said.
TT staff edited material submitted by the Mears Group, headquartered in Rosebush, Mich.