Pipebursting in Alabama

As part of the cafeteria renovation at Athens-Limestone Hospital in Athens, Ala., 155 ft of deteriorating 6-in. cast iron sewer pipe needed replacement. Camera investigation showed in places the pipe’s bottom was gone. Structures built over the sewer line complicated matters. The pipe ran 6 to 8 ft under two buildings. One of those was the hospital utility room containing its boilers and chillers. In fact, one boiler lay directly above the sewer’s path. The second building’s footing was immediately above the pipe, almost touching it.

Too Good to be True
Alan Shero, the hospital’s assistant administrator of support services, who also oversees facilities, said a project committee consisting of engineers, the primary contractor Robins & Morton and subcontractor Early Services studied three options. One involved disassembling the boiler, cutting through the concrete pad and trenching the pipe out. The second was not to dig but to construct a sewage lift up over the boiler facility, reconnecting with the sewer system on the other side. The third was pipe bursting, a technique, Shero said, that seemed just too good to be true.

“We’d seen video clips of it at work but we were skeptical. No one here had personal familiarity with it,” Shero said.

Jim Early is president and owner of Early Services in Decatur, Ala., a well-established third generation mechanical contractor specializing in commercial, industrial and institutional markets from Tennessee to Mississippi and central Alabama. It was Early who happened across pipe bursting technique online. He studied everything he could find on the Web about it and then contacted Brian Cowles, southeastern U.S. sales manager for HammerHead Trenchless Equipment of Oconomowoc, Wis.

Early said a presentation from Cowles put the team more at ease, but he himself was convinced from the start. “After watching the process on video, I knew that this is what we needed to do. I was very excited. This was something our company could handle, without a doubt,” Early said.

After two months of careful deliberation, Shero made the call to go with HammerHead.  
Studying the site and project specifications, HammerHead set up Early Services with a HammerHead HB100 static pipe-bursting system and sent Mark Maxwell, an experienced HammerHead ram and bursting technician, for onsite support.

For pipe, the team had considered SDR17 High Density Polyethylene Pipe but believed it would not hold up under the high temperatures coming out of the kitchen or boiler blow-down from the central plant. The team chose ductile iron, U.S. Pipe’s TR-Flex restrained joint system.

Pipe Bursting Techniques
Both pneumatic and static techniques send a bursting head through existing pipe, slicing or fragmenting it and pressing it away to the sides. In most applications replacement pipe is simultaneously pulled along behind the larger diameter bursting head. A larger diameter hole reduces friction as the pipe is pulled. Within a short time, the soil settles in around the new pipe as if nothing happened. No additional compaction is necessary. Incidentally, it most often means no indication at the surface that a pipe below has been replaced, minimizing restoration.

In both pneumatic and static techniques, the bursting head is launched at the entry pit. During pneumatic pulls, it advances in front of a piercing tool with a jackhammer-like action, a cable pulling ahead of it to guide it and help counter the increasing pipe drag. In a static pull, the head advances only as a result of being pulled by cable or pipe from the exit end. The pulling unit does all the work.

The static pull technique best matched conditions at Athens-Limestone Hospital, and a HydroBurst HB100 provided more than enough power from its 68 hp Kubota engine, which supports a hydraulic pump flow capacity of up to 43.6 gpm to as much as 4,060 psi.

All in a Day’s Work
The day prior to the launch, Early Services dug the entrance and exit pits. A HydroBurst HB100 was to be located in a 6-by-15-ft exit pit to a depth just below the existing pipe, but an overnight rain had caused the pit sides to slough off into the hole. Early services pumped the pit out and dressed its sides.

Early had ordered 18-ft lengths of the 6-in. ductile iron, which was the maximum he believed the limited working space would allow. The vendor sent 20-ft lengths. The confined working space between the structures made lengthening the entry pit a long and difficult process.

Maxwell wasn’t worried. He said some projects are ready to launch the minute he shows up, and others have lots of little obstacles to overcome. Pipe bursting doesn’t take long, and in spite of these pit issues, the HydroBurst was ready for a mid-afternoon launch.

The first tool into the existing sewer line was a pilot, a long section of pipe slightly smaller than the sewer pipe with two blades opposite each other to initiate fracturing of the brittle cast iron. A 10-in. IPS expander with outside diameter of 12.75 in. followed. Then each length of ductile iron replacement pipe, connected in the pit, was drawn behind the head in turn.

Average pressure during the pull was 12 tons, or “almost nothing,” Maxwell said, since the HB100 would give him up to 100 tons of pulling power if he needed it, the most pulling power in its class. The HB100 is compact enough to use for 3-in. pipe replacement but having that power gives a contractor the versatility to also replace water, sewer and gas lines up to 16 in. in diameter.

About 100 ft into the pull, the head was at the second building’s footing. The project team had hoped to save time without doing anything to the footing, but when Maxwell noted a difference in pull characteristics at the footwall, he stopped. The team authorized the crew to accommodate expansion under the wall. Hammering out the concrete and cutting away rebar added another six hours of tedious labor with hand tools to the project time but absolutely ensured the structure would be unaffected.

The burst continued thereafter to completion without a hitch. Maxwell said a well-prepared, uninterrupted 150-ft burst will usually take anywhere from 30 to 45 minutes. A HydroBurst can complete a 400-ft job, including payout and pullback, in just two hours.

Without a Doubt, the Way to Go
Shero said the hospital cafeteria prepared food in advance, so no services were interrupted during the burst.
Early said, “Pipe bursting was without a doubt the way to go,” estimating the hospital saved $110,000 by going trenchless.

Early was not only pleased with the technique but with HammerHead support. “Mark Maxwell was outstanding. He is a professional at what he does and knows this process like the back of his hand. He will be requested on our next project with Hammerhead. I will most definitely use this process again and have already bid a few projects based on it,” Early said.

Shero said he’d also use this technique again, given a similar application, which he described as “a straight run without too many laterals to tie in to it.”

“We were very pleased with the results and would use it again in the future, certainly,” Shero said.

Joe Bradfield is with Ellenbecker Communications.