What's New at AMERICAN - Underground Construction - March 2006Record Ductile Iron HDD Water ProjectParameters Continue To Be Expanded, Enhanced by Jeff Griffin -- Senior Editor Last summer in western New York, a 785-foot-long, horizontal directional drilling (HDD) installation placed 36-inch-diameter ductile iron pipe beneath a creek and flood control channel adjacent to an interstate highway.
At the time of the installation, the job was thought to be the longest segment of ductile iron pipe of that diameter ever to be installed by directional drilling. Trenchless construction methods are not new to ECWA, but the project marks the first time HDD was used to install pipe in its water system. Ralph Carpenter, marketing specialist and trenchless product manager at American Ductile Iron Pipe Co., Birmingham, AL, maker of the pipe installed on the project, says the job provides an excellent example of the value of directional drilling and illustrates the suitability of HDD for the installation of ductile iron pipe. Despite the popularity of plastic pipes, the use of ductile iron pipe for public works projects continues to be strong. "Like ECWA, other project owners and engineers in many parts of the country prefer the inherent strength, toughness and versatility of ductile iron pipe for their systems," said Carpenter. Yet some still hold the mistaken opinion that ductile iron pipe cannot be installed by HDD because joints will pull apart during the installation process. In fact, ductile iron pipe is just as suitable for installation by directional drilling and pipe-bursting procedures as is HDPE and PVC pipe, and in some respects may be even better suited for trenchless installations than plastic materials. Flexible restrained joints effectively hold ductile iron pipe together during the pulling process of both directional drilling and pipe bursting, while still allowing joints to deflect as a bore path changes direction. Concerns Early in the planning stages, ECWA and consulting engineers Erdman Anthony and Associates determined that open-cut construction for the channel crossing was cost-prohibitive and posed inherent risks. The channel protects extremely valuable upstream properties from flooding. A major rain event occurring while the channel was constricted, as it could be during construction, would make possible catastrophic flooding. Of trenchless options available, initially the conventional jack-and-bore method was selected as the preferred method. "This crossing followed a pretty tricky route, and, up until this time, the only way we had approached such situations was with jack-and-bore, but we wanted to consider alternative trenchless options," says Jim Ehrin, ECWA distribution engineer. In their investigations, Ehrin and Erdman Anthony documented that restrained joint ductile iron pipe had been successfully installed by directional drilling in other regions of the country. "I did some traveling to learn more about the procedure," Ehrin continues. "I saw some 6- or 8-inch-diameter pipes installed by HDD, but we would be putting in 36-inch pipe, and that's a big difference." During the process, Ehrin and Erdman Anthony engineers learned that Trans American Underground HDD (TAUG-HDD), Flower Mound, TX, had successfully installed 1,080 feet of 30-inch-diameter American Ductile Iron Flex-Ring Joint ductile iron pipe on a project in Texas. TAUG-HDD personnel assisted in calculating the pulling force that would be required to make the installation by directional drilling, confirming that the 36-inch-diameter Flex-Ring ductile iron pipe joints could accommodate those forces. Subsequently, ECWA chose to allow bids for both jack-and-bore and HDD. Five bids were received, the two lowest being for installing this segment of pipe by directional drilling. TAUG-HDD was selected as the HDD subcontractor. Smooth operation "The project went very smoothly," says Keith Whitaker, president of TAUG-HDD. An American Augers DD-330 with 300,000 pounds of pullback and 50,000 foot-pounds of rotary torque was used to make the installation. Tracking was done with DCI Eclipse walk-over tracking equipment. The pilot bore was surface-launched. Using 5-inch drill rod, the machine completed 800 feet of the pilot hole through soft to very soft clay in about six hours. Because of the soft soil conditions, the decision was made to add an additional 780 feet of rod which would become a tail rod. "The tail rod provides a guide for the reamer to follow during backreaming," says Whitaker. "In soils where stability of the pilot hole is at risk, we usually choose to use a tail rod." Beginning with a 24-inch-diameter fly cutter reamer, the drill unit pulled the hole opening tool back through the pilot bore. A 24-inch barrel swab then was pushed back through the hole. The next step was to repeat the procedure with a 36-inch-diameter reamer. Whitaker says the decision was made to forego an intermediate reaming step with a 48-inch tool and go to a 54-inch backreamer which is 1.26 times the pipe bell's outside diameter. The 54-inch reamer was pulled through the hole one time and a 48-inch barrel reamer swabbed the hole once again. Because there was a delay in assembling the pipe for the pull-in, it was necessary to swab the hole three additional times with the 48-inch tool in order to keep the hole open for the pipe pull-in. Project plans specified that the pipe sections be pulled in one joint at a time (labeled the cartridge method by the ductile iron pipe industry), an option that can be very important on job sites without sufficient space to connect and lay out and assemble pipe into a single string before pulling it back through the pilot hole. However, TAUG-HDD concluded soil conditions were not conducive to the one-pipe-at-a-time method and recommended pipe sections be assembled prior to installation. The primary concern revealed by cuttings carried out of the pilot hole by drilling fluid was that there was a greater risk of a collapse of the bore path if pipe was installed one length at a time. Pipe prep Pipe required double wrap of 8 mil polyethylene (PE) encasement installed in accordance with the guidelines provided by the pipe supplier. In addition, prior to application of the PE encasement, each pipe section required two No. 4 copper bonding jumpers per pipe section to make the pipeline electrically continuous so that the line can be tested and monitored. Each pipe section required the bell face to be drilled and tapped for two quarter-inch bolts and CAD-welded wires attached to the spigot end of the joint. After applying the PE encasement, each pipe section required exterior marks to identify the locations of the tapped holes and bonding jumpers. To facilitate pull-in, a guide ramp was constructed. Length of the ramp was limited to about 400 feet because an inoperable excavator blocked the pathway for assembled pipe, limiting available space for pipe assembly and requiring that the installation be made in two pulls. Pull-in of the first 400 feet was completed in 36 minutes, and the decision was made to assemble the remaining pipe into a single 380-foot string. This string took approximately 4 hours to assemble and only 36 minutes to pull through the pilot hole. Pulling force required never exceeded 75,000 pounds. During both pulls the polyethylene sheet, which was placed on the ramp to protect the double PE wrapping on the pipe, was constantly wet with a fire hose to reduce friction and maintain the integrity of the PE encasement. A coating of soap also helped reduce friction. Carpenter says that the Flex-Ring pipe is ideally suited for installation by directional drilling because the joint is designed to provide joint deflections, while maintaining full thrust capabilities. When deflection or articulation of the joint occurs, the wedge-shaped Flex-Ring segments slide up or down the mating wedge-shaped slope inside the Flex-Ring bell. This effectively distributes the thrust or pulling force around the bell face. "It is this functionality that makes Flex-Ring ideal on trenchless applications, including horizontal directional drilling and pipebursting of water and sewer lines," says Carpenter. For ECWA, its first experience with horizontal directional drilling was a significant success; by the first of the year, except for minor restoration, the project was complete and water flowed through the system. "We are very pleased," said Ehrin. "We actually were surprised about how flawlessly everything went and were surprised to learn after the job was finished that it had set a record for a ductile iron HDD project. We definitely will consider installing ductile iron pipe by HDD again when project conditions are right." For more information: |
The section of pipe was part of a project to upgrade the water system owned and operated by the Erie County Water Authority (ECWA), Cheektowaga, NY, bringing improved water-delivery capabilities to the town of Amherst in the northern part of the authority's service area.
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