October 2009 Vol. 64 No. 10
Features
Restrained Joint PVC Allows Obstacles To Be Overcome In Sewer Extension Project
As domestic oil production increases throughout the United States, so have the populations of western oil towns, such as Hobbs, NM, as hundreds of new people flock in to find work on the oil rigs.
This kind of growth has led to significant municipal water and sewer line extensions and improvements in the towns to serve the expanding population.
Last year, the city of Hobbs annexed 1,000 acres at the juncture of Dal Paso Street and Navajo Drive, two of its arterial roadways, for residential and retail development on the north side of town. The annexation was part of the city’s Dal Paso Navajo Corridor Strategic Growth Plan, which also included a sewer main extension of nearly 11,000 feet, and the installation of 51 sewer connections and 34 manholes. The new system was designed to tie in existing homes and businesses that previously had septic tanks and provide service for future development.
The city hired RPM Construction LLC, of Hobbs, for the massive infrastructure project in March 2008. The contractor was given the choice of what pipe materials to use on the project and method of installation. For the sewer main extension, they chose CertainTeed 8-inch SDR21 restrained joint PVC pipe, with installation by horizontal directional drilling. Using restrained joint PVC pipe in conjunction with directional drilling often provides an easier, faster installation, with fewer disturbances to the surrounding area.
“Directional boring typically helps the customer save money, since you’re not cutting up driveways or pavement as you would with an open cut installation,” says Robert Mendoza, owner of RPM Construction. “You don’t have to close off roads and driveways or restore the area after the project is finished. The restrained joint PVC pipe is durable and easy to install. It only takes two or three workers to put the pipe together during pullback. Plus, you don’t have to purchase or rent a fusing machine and spend extra time on joint fusion and cooling.”
CertainTeed’s innovative Certa Lok restrained joint technology requires no special heat fusion equipment, saving contractors a significant amount of time and money. PVC pipe joints are assembled during pullback, so streets remain open and clear, and the pipe is available in shorter 10 foot lengths to simplify assembly in the often confined spaces of directional bored sewer and pipe bursting jobs. When compared to alternate thermoplastic materials, higher strength PVC also requires a much thinner wall in order to achieve the same pressure rating.
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 24×40 (24,000 pounds of pullback; 4,000 feet pounds of radial torque) and a Vermeer 36×50 (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.
“We were pleased with the overall project and how responsive the contractor was in correcting any slope deficiencies in the sewer line,” Randall says.
RPM Construction was satisfied with the project’s outcome as well. “We usually work on smaller boring projects, and we took the Navajo Project as a great learning experience,” Romero says. “We had some bumps in the road with this project, but at the end of it, we came through, and we continue to use directional boring with success on other projects.”
FOR MORE INFORMATION:
RPM Construction, (575) 738 0110, www.rpmconst.com
Pipe Distributor: HD Supply, El Paso, Texas, (915) 590 6922, www.hdsupply.com
PVC Pipe and Joints: CertainTeed, (866) CT4 PIPE, www.certainteed.com
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