Using Pipe Bursting to Install a New Main in Soggy Ground
Built on an ancient lakebed halfway between Indianapolis and Louisville, the city of Seymour, Indiana, lies about 10 ft lower than the land around it. That means any work at depths much greater than 5 ft generally requires a week of de-watering prior to breaking ground. It’s routine work for Seymour-based Lawyer Excavation Inc., serving the region for more than 20 years with specialties that include site preparation and clearing, digging foundations, and performing storm, sanitary and water utilities work.
With more than 20 years of experience in the industry between them, Glenn and Darrin Lawyer established the company in 1995. After dewatering the worksite, Glenn Lawyer said the majority of the jobs are “pretty much straightforward excavation work.” Dewatering, however, is always a requirement.
“Some places we find the water table at 5 ft and in others 10 ft,” Lawyer said. “When you dig much below that, water continuously weeps from the soil into the excavation in a steady, slow release.”
He said the crew can generally set dewatering wells around the work area and run their hoses through a manifold to a single 6-in. diesel pump. “We’ll redirect the ground water to a storm sewer or just far enough away from the work area that it’s not a factor,” Lawyer said.
Yet even dewatered, excavating in proximity to building foundations is risky, as ground supporting the foundation is freed to move toward the cut. To replace or upsize pipe near buildings, Lawyer Excavation relies on the pipe bursting method.
For smaller diameter pipe bursts the company uses its own HammerHead PB30 30-ton cable pulling system. “We don’t just do pipe bursting for ourselves. We’ll use it to help out area plumbers who run into tough situations. As far as I know, we’re the only ones in the area who do that,” Lawyer said.
For larger diameter pipe replacement, Lawyer Excavation rents machinery and tooling matched to the specific job directly with HammerHead Trenchless When a blockage occurred in one neighborhood’s 16-in. asbestos cement (AC) gravity sewer main, the city called Lawyer Excavation for the repair.
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Lawyer Excavation located the blockage using closed-circuit television, discovering that the pipe had partially collapsed at a service saddle coupling. Rather than re-repair the aging AC pipe, Lawyer Excavation recommended replacing the entire section between manholes with new HDPE pipe. They set up temporary bypass sewage collection and prepared to replace the main using the pipe bursting method. “There really was no other way to do it,” Lawyer said. “Buildings were right in the easement.”
Lawyer consulted HammerHead Trenchless rep Nate Hrabosky. Lawyer was introduced to Hrabosky about six years ago as his company prepared for its first pipe bursting job. “Nate was very helpful, and has been ever since. It’s a relief, knowing they have your back,” he said.
Since no two projects are exactly the same, Lawyer Excavation benefits from consulting with an equipment manufacturer that is also a leading industry expert in pipe bursting applications. For this job, HammerHead Trenchless specified an HB125 static pipe-bursting system. The system is designed for use in pipe diameters 6 to 20 in. with 125-ton pullback capacity and includes a downhole pulling unit and 4,500 psi hydraulic powerpack. HammerHead Trenchless pipe bursting specialist Kent Westendorf was onsite to assist in the pipe bursting operation.
Dewatering continued steadily for one full week before the burst. Seymour’s ground conditions are sandy, varying in fineness over relatively short distances. Lawyer set a series of 2-in. dewatering wells around the launch pit, but in the finer sand around the machine pit, which held more water, they placed 4-in. wells. They also placed wells around the manhole to prevent groundwater from washing sand into the hole they would cut for the bursting tooling and new pipe to pass through.
The crew exposed and removed the line’s failed coupling. They widened the excavation and shored it up to create a 5-ft by 15-ft launch pit, a length sufficient to transition the fused up HDPE to the grade of the sewer line.
The machine pit was reinforced with 10-in. steel I-beams and several road plates to create a firm face capable of bearing the full force of the HB125 during bursting operations.
Lawyer Excavation had fused up the full 560-ft length of HDPE pipe on the surface two days in advance of the pipe bursting operation. “We wanted this done all in one shot, one pull,” Lawyer said. “Stopping to fuse up pipe would take too long.” The HDPE pipe was laid alongside the road, permitting traffic to continue on the street.
The only logistical complication, Lawyer explained, was, “Normally we pull pipe in straight.” But in this case, they could not. They had curved the 560-ft length of pipe 90 degrees around the corner of the block, laying it to one side. This kept the intersection open to normal traffic until they could do the burst. But pulling on the pipe as it now lay would drag it up over the corner of the block onto a residential lawn. And as it moved, the trailing end could whip straight, aligning itself with the direction of the pull, impacting properties on the other side of the side street.
The crew used its wheel loaders to prevent undesired pipe travel. One straddled the trailing end of the pipe, limiting its lateral movement with its tires. At the corner, the wheels of another loader served as a guidepost, preventing the pipe from creeping onto private property. Throughout the pull, the pipe remained on track in the street.
“Pulling around the wheel loaders did require more force, but the angle was wide enough that it really didn’t turn out to be that much. The pipe slipped along just fine.”
It had rained heavily while the crew was preparing the launch and machine pits, as well as the evening before the pipe bursting operation was to take place. More was forecast for the next evening. Before the crew could take advantage of the short break in the weather, they had to clean the machine pit of all sand and silt that had washed in overnight. They laid steel plate on the bottom of the pit and lowered the HB125 pulling machine into position. The crew paid out the pipe bursting system’s 39-in. pull rods stick by stick through the deteriorated 16-in. AC pipe to the launch pit.
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The crews waited until 9 a.m. to begin the pullback, leaving the streets open for morning commuters and school buses to complete their morning routes. When traffic died down, the crew pulled the pipe into position, fusing it to the pipe puller on the bursting assembly. Ahead of the fuse-on puller was the expander, which would cut the AC pipe open and expand the pipe path about 25 percent larger than the 14-in. DIPS HDPE replacement pipe’s OD, reducing friction for a smooth operation. The pipe pilot and swivel connection completed the bursting assembly. After the crew removed the protective push cone from pulls rods and attached the bursting assembly, pullback began.
The HB125 pressure gauge read 90 tons as the expander engaged the old pipe, then subsided to approximately 50 tons for most of the burst. At a manhole mid-run, the machine briefly required 90 tons of pulling force again. At times, all 125 tons of pullback capacity was briefly called upon during the bursting operations.
Lawyer Excavation completed the run within just three hours. Since pipe is racked as it is retrieved, removing the bursting machine from the pit was quick, leaving the crew time to tie in the new pipe and reconnect the services in the remainder of the day.
Lawyer said, “When you consider all that it would require to trench that up, the work protecting those houses, all the restoration involved, the pipe bursting method is easily the most cost-effective and safest way to have done this job.”
Joe Bradfield is senior writer for Ellenbecker Communications, an international communications firm specializing in the drilling, mining and construction industries.