September 21, 2016With experience pipe bursting water mains since the trend’s beginnings in the United States, a municipal engineer and a private contractor share their expertise
Originally developed in Britain for replacing 3- and 4-in. cast iron gas mains, the pipe bursting technique has been evolving over the past three decades on both sides of the Atlantic. So have the techniques, equipment and materials used in pipe bursting. HDPE and fusible PVC not only have longer useful lives and better flow characteristics than the original pipe materials they replace, but they also facilitate faster, more economical project completion.
For the first 20 years in the United States, however, pipe bursting seemed regarded solely as a sewer replacement technique. A little more than a decade ago, municipalities tending to aging water delivery infrastructure began seeing its value for water lines, as well.
Two pioneers in this pipe bursting application, one a city employee, the other a private contractor, share their pipe bursting insights and passion as pioneers in this application.
As distribution and collection superintendent for the Public Works Department of Billings, Mont., Scott Emerick said he is always interested in techniques and equipment providing more cost-efficient water and wastewater infrastructure management. Yet his knowledge of newer trenchless techniques more than a decade ago was limited to what he could read. It just wasn’t being done anywhere nearby yet. Then a failed 24-in. storm sewer offered him a firsthand demonstration of a HammerHead HydroGuide HG12 Auto Boom Winch.
Conveniently designed to accommodate use in both manhole and pit accesses, the winch’s patented self-deploying downrigger is positioned in close alignment with the pipe’s orientation for the most efficient use of its pulling force (up to 12 tons). Its ease of use can save hours on project setup labor and minimizes time in the hole. Cable paid out from the downrigger at one end of the pipe draws tools, lining or product pipe of a particular application back toward itself. Applications include pipe bursting, slip lining, swage lining, and cable and pipe pulling projects.
In this case, Emerick used the HG12 to slip line the sewer with 20-in. HDPE pipe, but the demonstration convinced him that he and his city crews could master this. And it led him to take the next step: pipe bursting.
Emerick and his crews had continuing success with pipe bursting techniques, first with another storm sewer and then a sanitary sewer. “That got us thinking, ‘Why not try it for our water lines,?’” he said.
A local contractor loaned the City of Billings a HammerHead HydroBurst HB80, an 80-ton hydraulic pulling machine for static pipe bursting applications. The HB80 has more than six times the pulling force of the winch-style HG12, which is delivered through the HB80’s connectible pulling rods rather than a cable. The rods are joined up one by one as they are paid out and then removed one at a time as the machine pulls the bursting tool, or “expander,” and attached product pipe back to itself.
After upsizing 300 ft of 4-in. cast iron water main to 8-in. HDPE pipe, the City purchased its own machine, a 100-ton HammerHead bursting system.
In addition to storm sewers, sanitary sewers and water mains, Billings also replaced irrigation lines for the park department. “Ten years later now, and we’ve become experts at pipe bursting, though we’re still learning something every job,” Emerick said. A professional engineer, Emerick presented a paper thoroughly detailing the City’s use of pipe bursting the 2015 NASTT No-Dig Show in Denver.
Today, Billings allots about $4 million annually for its water and sewer main replacement program. Pipe bursting has allowed Emerick’s department to stretch that budget by completing some of the projects at one-quarter to one-third the cost contracting them out as open cut. The City replaces 7,000 to 8,000 ft of pipe a year in a system comprising 436 miles of water main and 433 miles of sanitary sewer main, including 3,800 fire hydrants and six sewer lift stations. The more the City can burst on its own, the better, Emerick said, “But of course we can’t do it all. That’s impossible.”
Some of the work is intentionally left to contractors who have the equipment and experience necessary to dig the deeper access pits that are required for some of the runs. “This is Montana,” Emerick explained. “Our northern climate requires water lines and sewers to be at least 6 to 6 ½ ft and can be deeper to navigate other utilities. To dig pits much deeper than 15 ft is typically beyond our capability.”
And not all of the footage scheduled for replacement qualifies for the pipe bursting technique. Since the pipe bursting technique follows the path of the existing pipe, adjusting an existing utility’s grade or depth means bidding the project out as open cut. “And there are lines where you have services connecting every 25 ft. You’re going to be tearing up the road and replacing it anyway, so there’s really no point to pipe bursting a line like that.”
When city officials from other municipalities ask him for advice about starting up their own in-house pipe bursting programs, he said he can only speak for Billings and the unique situation that works for his department. “It depends so much on what their tax base is,” Emerick said, “and the availability of contractors, their resources, their project design, who is dealing with the administration end of it and the construction end of it.”
An in-house pipe bursting crew has made sense in Billings, which has prioritized its water distribution and collection system. The technique helps Billings maintain a remarkable water loss record of less than 5 percent. Emerick said, “We’ve been replacing pipe since 1980. The city makes sure funding is in place, we’re invested in the technology, we’ve become very good at what we do and we keep on it.”
Like Emerick, Mark DiMichele, owner of D&D Sewer & Water in Canton, Mich., is also enthusiastic about spreading the word of pipe bursting’s advantages. And he is also a seasoned expert in the technique, having been involved with water main pipe bursting since its first introduction to the Detroit area 10 years ago.
“We were underground construction specialists at the time,” DiMichele said. “We’d been subcontracted to do residential hookups by a British pipe bursting company on a big, two-year-long replacement job. We developed a good relationship and had learned enough in a year of working around pipe bursting operations with them every day, to offer to finish the project while they went on to their next big job.”
Ten years later, municipal pipe bursting accounts for about 60 percent of the D&D’s work in a service area extending in a 100-mile radius from its base of operations.
HammerHead Trenchless Equipment, DiMichele’s choice for his pulling machine, regarded his expertise so highly that it asked him to help in the design of a new 100-ton machine. DiMichele put the prototype’s design to the test in arduous, real-life field conditions — including some features he himself suggested. Now he owns the first HammerHead HydroBurst 100XT to come off the production line. Rated for 98 tons of pulling force, the 100XT bursting machine’s onboard computer can run the hydraulics in either a 100-ton mode or 50-ton mode.
The 50-ton mode directs all available hydraulic fluid to just two of the unit’s four cylinders. This allows the contractor not only to use the puller on smaller jobs but at a faster bursting speed. Even on jobs that require accessing its full pulling force, payout can still be completed twice as fast using 50-ton mode — 15 ft per minute to 400 ft.
The unit also features an automated rod spinning assembly and tethered remote control. The new spinner assembly allows continuous feeding of lightweight 2.5-in., API-threaded straight pull rods. The operator does not need to stop the machine to add rods.
A remote control puts DiMichele or one of his other operators on the surface, freeing up workspace in the pit for the rod handler, permitting the best view for more efficient control of the operation. Lever-actuated controls on the puller itself facilitate initial training and orientation at the machine and provide redundant backup, ensuring job completion if for any reason the remote control cannot be used.
The 100XT is only 39 in. high by 30 in. wide, so working pit dimensions can be smaller, perfect for the narrower side streets of many residential areas DiMichele works in.
DiMichele considers the pipe bursting method to still be evolving. The hard part, he said, is educating project owners that there’s a newer, better way to do things. “It’s just human nature. It’s hard to persuade any of us, I think, to look at new methods when we expected to do it the way it’s been done a hundred years. Like using iron pipe. If we can get people to move away from ductile iron pipe, then they will really get to see the advantages of pipe bursting.”
DiMichele said he does install ductile with pipe bursting technique, but it’s not as conducive to pipe bursting as HDPE or fusible PVC. These plastics offer a tremendous advantage of making lengths of 300- to 500-ft main on the surface to install it all at once in a single day. This is fundamental to the pre-chlorinated pipe installation method. “Pre-chlorinated method can’t be done with ductile iron.”
Municipal engineers specify pre-chlorinated installation for its main selling point: greatly reduced impact on the water system’s end users. Water customers typically lose service for only one workday shift. Restoration is limited to service accesses and the pulling pit. Streets, driveways and lawns typically remain untouched.
This is in stark contrast to an open-cut replacement of a water main, a process, DiMichele said, in which lawns, driveways, trees and streets are unavoidably damaged. And individual services for an open cut replacement are not just disconnected but must each be connected to an alternate water source for the duration of the project — generally one to two weeks.
Once pipe is removed and new pipe is made up, the cleaning and sterilization process begins to make the conduit safe for use with drinking water. Chlorination and testing usually last several days. When the pipe is ready, the services must be taken one by one from their temporary bypass and reconnected to the main. Once everything is running, restoration can begin. It’s a long intrusive process —that can be avoided with pre-chlorinated pipe replacement method.
But it’s also a technique that calls for a specialist with crews dedicated to the job, working uninterrupted start to finish, DiMichele said. Therefore, the method’s critical choreography rules out many in-house municipal pipe bursting programs. “Those city guys wear lots of hats,” DiMichele said. “During a job they can be called away to deal with an emergency elsewhere in the city.” DiMichele, on the other hand, dedicates crews solely to the project before them.
Most of the municipal installations for D&D’s service area are 8 on 8 replacements, the most common diameter for distribution mains there. Those lines laid with 6-in. pipe are almost always upsized to 8. And D&D’s crews have also done 12 on 12 and even a 12 to 16 upsize. “The 16-in. we replaced was for a major trunk line.”
The projects are orchestrated in 300- to 500-ft runs, judging what D&D believes can be made within the specified timeframe. In shorter runs, the complete job – from staging, digging the pits and completing the burst and reconnections — can be done the same day. On longer runs they’ll prepare the location the day before. “We put in some long days, 10 to12 hours. As soon as the water’s on, then there’s clean up, filling in accesses, grading, seeding.” In comparison, “It typically takes two weeks for an eight-person crew to install 1,000 ft of new water main with open cut method.”
Municipalities and private contractors alike have discovered another benefit in choosing the pipe bursting technique for water line replacement. Much of the water line in the United States is now reaching the end of its useful life is asbestos-cement (AC) pipe. Although generally considered non-friable, all AC pipe removed from the ground requires disposal according to stringent asbestos abatement guidelines. Weathered or deteriorated AC, however, is a project-stopper. Since pipe bursting technique leaves the AC pipe in the ground unexposed, the pipe requires no treatment at all, offering a tremendous advantage over other replacement techniques.
Whether it’s stretching the city’s budget, minimizing disruption to its citizens’ routines or minimizing environmental impact, pipe bursting is coming of age in the United States.