January 1, 2008After learning that fusible PVC pipe can be a viable alternative for pipe installation, through various projects such as a wastewater force main in Bridgeport, W.Va., directional drillers from around the United States are starting to use this piping as part of their HDD projects. Upon successful completion of numerous projects utilizing fusible PVC, contractors show that the pipe and HDD can in fact work together.
H&H Enterprises, Andover, Ohio, was subcontracted by D&M Contracting Inc., New Alexandria, Pa., for the project that required 400 ft of 16-in. fusible PVC pipe to be installed via directional drilling under a creek and ravine. This pipe would connect to a new bell-and-spigot PVC line leading to a wastewater treatment plant. This bore was part of a larger project that was mostly using open-cut to provide sewer service to a new hospital and a new federal building.
Thrasher Engineers, Clarksburg, W.Va., — which was designing a project with fusible PVC for the first time — and D&M Contracting selected HDD for this 400-ft section of the project, as it was a cost-effective alternative to open-cutting the ravine, which had ground conditions consisting of gray sandstone. HDD also provided for a quicker project turnaround.
D&M Contracting provided the necessary exit and entrance side excavations. Once the entrance and exit pits were completed, H&H mobilized its equipment, which included an American Augers DD-6 directional drill, MCM 2000 mud recycling system and Gardner Denver TGEE mud pump. H&H began the project — the first time H&H used fusible PVC — with a thorough evaluation of the existing site conditions, engineering plans and HDD design. Initial work before actual boring included locating existing utilities and finalizing the bore path.
To drill the pilot hole, H&H used a 5.25-in. tri-cone drill bit, powered by a mud motor.
“The pilot hole went smoothly and the depth and alignment were exactly as required by the project owner and engineer,” said Jason Hockran, vice president and owner of H&H Enterprises. “The key to drilling the pilot hole was ensuring the bend radius of the pipe was not exceeded.”
Upon completing the pilot hole, multiple hole-opening passes were needed to enlarge it for the product pipe. H&H started with a 10-in. tri-cone hole opener and moved up in steps of 14, 18 and 22 in. until the final pass was completed using a 26-in. hole opener.
Hockran noted that the H&H crew faced some challenge with the ground conditions. “The most challenging aspect of the job was drilling the pilot hole in rock [gray sandstone],” Hockran said. “Once it was complete and in the proper location and alignment, the complexities of the job were completed. Much of the HDD part of the project was left, as the hole-opening had to be completed. Opening a 26-in. hole in rock can sometimes pose problems in an area due to unconsolidated formations such as clay stringers, but in this case we did not encounter any.”
Fusible PVC Used
Underground Solutions (UGSI) provided the 16-in., DR18, fusible PVC (FPVC) pipe, as well as its fusion services. UGSI regional sales manager Rob Biase said FPVC was used for 400 ft of the project because it’s the same material as the bell-and-spigot PVC. “It allowed for the necessary internal diameter to meet the flow requirements,” Biase said.
D&M Contracting also recognized the advantages of being able to complete current and future connections using standard ductile iron pipe fittings and PVC joint restraints, Biase said, noting that municipalities and local distributors stock ductile iron pipe size fittings and PVC restrainers vs. the “uncommon” iron pipe size, thereby making connections, reconnections future expansions and potential repairs fairly simple, as well as on time.
The fusion process went smoothly, with UGSI fusing 10 lengths of the pipe in 40-ft sections. The process took about three days. “The fusion went very well,” Biase said. “It was a great setup in terms of logistics, mainly because there was a right of way where there was plenty of room to actually fuse and stage.”
The pipe fusion was done just as the H&H crew was ready for pullback. The entire project took about two weeks.
Biase said that H&H was a little skeptical at pulling back FPVC when the project first started, but was satisfied with the results. “Whenever you have a relatively new product such as FPVC, some directional drillers are skeptical about the flexibility and strength of the PVC,” he said. “We have to convince them that there’s nothing to worry about. But until they actually pull it and see it … [H&H] was kind of surprised not only by the strength but the flexibility of the PVC. So the company’s preconception of the pipe was not true in terms of how flexible it is and how easily it can be pulled in for a directional drilling application.”
H&H was initially concerned with the bend radius of the pipe. “In most circumstances with plastic pipe, the steel drill pipe bend radius is the limiting factor,” Hockran said. “That was also the case here but due to the restrictions of the PVC pipe, we had to pay closer attention to the bend radius as we drilled the pilot hole. In doing so, we drilled a very smooth transitioning hole, which provided for a better hole-opening and installation.”
The use of FPVC pipe in directional drilling projects is becoming more accepted as more HDD contractors use it and believe in its capabilities, Biase said. “Fusible PVC is a relatively new product and when I say relatively new, our company is about seven years old,” he said. “But today, we have the personnel and [support] to go out and demonstrate to people what this product can do.”
Although FPVC is still not the top pipe of choice in the HDD market, it has grown in other trenchless markets. “FPVC is used in a variety of trenchless applications,” Biase said. “It’s been used on pipe bursting projects, sliplining projects and now we are starting to see people consider FPVC on dig-and-replace projects. Certainly the benefits of a fused joint and a leak-free gasketed system are apparent whether you pull it in [using directional drilling] or put it in conventionally with open-cut.
“Not many people knew that PVC could be fused,” he added. “Once the word was out that it could be fused, then it became the product of choice for many because of the properties of PVC as a water pipe material.”
Sharon M. Bueno is managing editor of Trenchless Technology.