The record “pull” is one of four HDD installations completed as part of a 32-mile ductile iron pipeline that will carry treated wastewater from Meridian, Miss., to a new industrial facility northeast of the city. The three shorter pulls were 1,000 feet, 880 feet and 880 feet.
Since 1996, HDD has grown in popularity as an alternative method of pipe installation.
“Our customers use HDD in situations where open cut trenches are not desirable, for instance under waterways, roadways, congested areas or environmentally sensitive areas,” said Ralph Carpenter, project manager with American Ductile Iron Pipe, a division of American Cast Iron Pipe Company, in Birmingham, Ala.
With HDD, a gentle arcing pathway, called a bore path, is drilled underneath an object or area. Then, a tool called a reamer is used to enlarge the bore path greater than the diameter of the pipe being installed. This can take several passes, enlarging several inches at a time. Finally, the pipe is pulled through, completing the process.
During the design phase, engineers estimate the pullback force required to pull the pipe back through the bore path.
“The allowable pull load for these four sections of pipe was 310,000 pounds,” Carpenter said. “One pull, through an old landfill area, tested our calculations, nearly reaching the allowable limit. With the other three pulls, the applied loads were less than half the allowable limit.”
Layne Heavy Civil, Fairborn, Ga., the general contractor for the project, and subcontractor REM Directional, Boligee, Ala., were responsible for pipe assembly and drilling the bore path.
“Contractors preassembled two standard 20-foot sections of pipe above ground, making multiple 40-foot sections, and staged them near where the pipe would enter the bore path,” Carpenter said. “This was a novel approach that saved a considerable amount of time.”
Ductile iron was selected as the pipe material for this project early on due, in part, to its strength and reliability.
“This pipeline, when complete, will span some 30-plus miles, which means fairly high water pressures; this is a job for ductile iron pipe,” Carpenter said.
From pre-design to completion, the record-breaking pull was a team effort, Carpenter said.
“This project is a prime example of the advantages of ductile iron pipe, HDD installation and American’s knowledge and experience with HDD technology,” he said.
