Restrained Joint PVC Allows Obstacles To Be Overcome In Sewer Extension Project

October 2009 Vol. 64 No. 10
RPM Construction used CertaFlo Greenline 8 inch SDR21 restrained joint PVC in a recent 11,000 foot sewer extension in Hobbs, NM.

Work begins
RPM Construction began work in July 2008, using a crew of six – three working on the drill and three assembling pipe. Using a Vermeer 24x40 (24,000 pounds of pullback; 4,000 feet pounds of radial torque) and a Vermeer 36x50 (36,000 pounds of pullback; 5,000 feet pounds of radial torque), the crew drilled through a rough mix of sandstone and caliche. Excavations were made with a John Deere excavator. Bore length ranged from 320 to 600 feet, with a maximum depth of 13 feet.

Instead of using a standard pilot drill bit, the crew used a Straightline 4 inch air hammer system to simplify boring through rock and to keep the sewer line on grade, which proved to be the biggest challenge of the project. The city of Hobbs required the contractor to install the sewer line on grade at a .022 percent slope and perform flow tests and underground camera inspections tests to monitor the sewer line’s adherence to the grade. Unfortunately, the rocky soil and low slope of the land made staying on grade impossible in some parts.

“The air hammer kept us close to staying on grade, but it was still a big challenge,” says Miguel Romero, business development coordinator for RPM Construction. “It was great practice for our crew to try to keep the grade for this project, but at the end of the day, we had to trench a small portion of it.”

“If the land had a steeper slope, directional boring would have worked perfectly,” says Hobbs City Engineer Todd Randall. “But, with a flat slope like we had on this project, it’s not always practical without using some of the newer techniques that are now available for maintaining precise grade with HDD.”

To meet grade requirements, the crew excavated and unearthed about 2,000 feet of pipe and reinstalled it by hand in an open trench to meet grade requirements. While disassembling the restrained joint PVC pipe, the crew had some difficulty, as it is designed to hold firmly together during pullback and in service. Once separated and moved to the desired location, however, the pipe was easily reassembled. These revisions would likely not have been possible had HDPE or another fusible pipe been used.

“It would have been a lot more difficult with the fused HDPE,” Randall says. “They might have been able to salvage some of it, but it would have been much more labor intensive.”

Even with these challenges, RPM Construction still completed the 360 day project on time this July. The sewer lines passed all pressure tests and met grade requirements and met with the customer’s approval.