Contractor Merges Experience With New Ideas; Effects Burst, Replacement of Collapsed Sewer

In the beginning, there were three choices. Trench it, repair it, or burst it.

The “it” was a 230 foot length of sanitary sewer pipe that was failing in Greenville, SC. It needed attention and the Western Carolina Regional Sewer Authority (WCRSA), responsible for maintaining the line, had allowed the following three methods of replacement: trench and replace, point repair prior to pipe lining, or pipe bursting and replacement.

The existing 10 inch vitrified clay pipe was acting its age. Installed decades ago beneath tons of dirt and fill, it was beginning to crumble and was near collapse at one point. This near collapse appeared to be the result of an obstruction lodged in the pipe. Strangely enough, the two did not correlate.

This situation was previously documented when Southeast Pipe Survey (SPS) of Patterson, GA, was contracted by WCRSA to clean and televise the line. Upon review of this information, only one of the three methods originally considered remained–pipe bursting.

Pipe lining could not be performed without first performing an expensive 20 linear foot point repair to correct the partial collapse of the line. Open trenching was determined to be too expensive and disruptive, as the trenching would run from a four lane highway through a strip mall parking lot. What’s more, a creek tunnel traveled beneath the parking lot, making it difficult to excavate without the possibility of damaging it.

This final decision to use pipe bursting was made when SPS President David Herrin consulted with Western Carolina’s I/I Coordinator Marion Boone. Boone had first become aware of the pipe bursting methods through seminars, trade publication articles, and video tapes of the trenchless process.

Although it didn’t apply in this application, Boone said that pipe bursting has another big advantage over other processes. The way he sees it, pipe bursting is the only rehabilitation method that offers the ability to upsize pipe, thereby dramatically increasing flow potential.

Having been established as the most cost-effective method, pipe bursting also offered the least amount of street and parking lot disruption. SPS then submitted a bid to burst the failing line in Greenville.

Contractor Is Convinced

SPS’s Herrin had become acquainted with pneumatic trenchless tools about a year before the Greenville job. In early 1994, he attended a pipe bursting demonstration held at the TT Technologies North American Headquarters in Aurora, IL. TT Technologies is a manufacturer of trenchless tools and equipment.

There he saw first hand the capabilities of Grundocrack pneumatic pipe bursting tools that burst old pipe and install new polyethylene (PE) pipe in a one step process. He watched as the pneumatic tool and expander were launched into the existing pipe. Located at the exit pit, a winch provided constant tension to the tool.

Along with the bursting tool demo, Herrin also witnessed a piercing tool in action and became very intrigued. After lengthy discussions with several manufacturer representatives about various tool’s performance, he became convinced to make an investment in these tools.

As a professional with over 15 years experience in maintenance, inspection and rehabilitation of pipe systems, Herrin is always interested in finding better ways to perform his job.

Within the past year, Herrin has purchased several tools and accessories for his contracting business’ trenchless requirements, including piercing, bursting, and bursting support tools. Now he had the perfect solutions to the complexities of the Greenville burst.

“This was an extremely difficult project,” stated Herrin. “The parking lot manhole was 26 feet deep and the exit manhole in the middle of a four lane highway measured 13 feet deep. In addition, there was a 10 foot by 10 foot diameter tunnel running parallel and adjacent to the sewer line.”

The failed pipe section was below a parking lot in front of the strip mall. The primary tenant is a grocery store, so both vehicle and pedestrian traffic is very heavy throughout the day and evening hours. The tool and continuous length of PE pipe could not be fed into the existing manhole. To launch the bursting tool from the parking lot meant some excavation to create an entry pit. Herrin knew that trenching would certainly work, but it was far from ideal. It would congest traffic in the parking lot, create a potential hazard for pedestrians, and above all, increase the cost of the project. Although not completely obvious at first, Herrin realized another possibility.

Point Of Entry Determined

Herrin pursued the innovative option of launching from the underground creek tunnel. This plan would depend heavily on Herrin’s experience and his assortment of recently purchased trenchless tools. The plan was to use a 3 inch diameter piercing tool to produce a pilot bore from the parking lot manhole to the adjacent tunnel. It would be shot at a 10 degree upward angle to perfectly intersect the tunnel wall, maintaining the necessary trajectory. This would allow the bursting tool to be easily launched from the tunnel.

Herrin’s idea was then set into motion. All was going well until the piercing tool encountered the tunnel wall. Most of the tunnel was made of rock, but this particular section was constructed of 12 inch thick reinforced concrete. The piercing tool simply could not penetrate it. The work had unexpectedly come to a halt, but only temporarily.

After securing the necessary clearance from the WCRSA and the City of Greenville, SPS crews used a jackhammer to bore from inside the tunnel to meet up with the pilot bore. They isolated the hammering sound of piercing tool against the wall of the tunnel to indicate the exact point to target. The bursting tool was then brought into the tunnel to be connected to the winch line. The next challenge was to feed the line through the old pipe (from the exit point) to the bursting tool waiting at the entry bore.

SPS came up with a solution to feed the winch line through the pipe. They brought in a sewer/vacuum truck which is used to clean sewer pipe by propelling a high pressure water hose through the line. The truck was positioned at the exit point (highway manhole), with the hose lowered down to the decayed pipe.

With water pressure applied, the hose shot down the line. Once the hose reached the entry bore, crews attached the winch line, and then reeled the hose back to the truck. It both cleaned the line and provided a way to pull back the winch line.

A pilot bore was also on the agenda to facilitate the exit of the tool from the highway manhole. The idea was to set up a trailer mounted constant tension winch directly in line with the burst. This was a possibility because at this point, the highway runs along the edge of a vacant lot, providing an ideal location for an access pit.

A piercing tool was lowered into the highway manhole to be shot out the side of the small pit. This would allow the winch line to pull from the side of the highway, instead of from the manhole opening in the middle of the four lane road.

A bore was easily performed, but the wet soil refused to cooperate. Almost as quickly as the tool exited the pit, the bore filled in. SPS crews had hoped to complete this bore so that the Grundocrack tool could exit from the pit instead of the manhole. Since this was no longer an option, it was back up to the middle of the road surface for the winch set-up.

It was uncertain whether the tool could be removed from the highway manhole without some excavation. Herrin figured that once the bursting tool reached the highway manhole, they could come up with a suitable solution. In fact, he had an idea or two in the back of his mind.

The Burst

Now, it was show time. Herrin assembled his pipe bursting system which included a Grundocrack Olympus pipe bursting tool, 12″ head expander, and Grundowinch 10 ton trailer-mounted winch. The tools used to perform the pilot bores were Grundomat piercing tools. On hand throughout the project as a manufacturers representative was Eddie Ward, Southeastern Regional Sales Manager for TT Technologies.

The Grundocrack Olympus is a smaller pipe bursting tool than would normally be used in an application of this nature. It was selected for a very important reason. As previously mentioned, the point of entry was a hole established through a tunnel wall with the pilot bore angled to intersect the adjacent pipe. WCRSA had a concern that the vibration caused by the percussive action of the tool in the near-by pipe might cause some structural damage to the tunnel wall. With this in mind, SPS elected to use an Olympus tool that purchased less vibration, but was powerful enough to get the job done.

SPS used the Grundocrack Olympus to burst the 30 year-old vitrified clay pipe and replace it with 10 inch diameter SDR 11 HDPE pipe in just one step. This resulted in a significant cost savings for the WCRSA. “We could not have done the project without the versatility of the tools,” exclaimed Herrin.

It took six hours to complete the actual burst and replace of the 230 feet of sewer line. The tool had started off swiftly, but slowed down dramatically about midway through the burst. It would take twice as long for the tool to accomplish the second half of the burst as opposed to the first half.

Questions arose about whether the Olympus tool had enough power to perform this job. This concern was quickly dispelled when the tool showed up in the exit manhole toting a cement point repair. This explained the slow-down. Crews were then surprised by the tool’s tenacity.

Once the tool reached the highway manhole, the Grundowinch was repositioned in the small exit pit. Herrin’s crews had left a winch line in a previous bore, which they were able to attach to the head of the bursting tool. The winch line was then reconnected to the winch, allowing the tool to be pulled completely into the manhole.

With the PE pipe exposed, crews were able to separate it from the tool. The approximately five foot long tool with expander was then easily lifted out of the manhole. Herrin offered, “We were able to remove the tool from the manhole without any highway excavation.”

Even with the obstacles and occasional problems with logistics, the entire project was accomplished within a thirty day time frame and under budget. “It was a pretty fast process from start to finish, even though they (SPS) had lots of hoops to jump through in preparation,” commented Boone.

Herrin looks forward to performing at least three more pipe bursts before autumn. He’ll be bringing his bursting tools, along with the experience he gained in Greenville.

 

Pipeline & Utilities Construction, July 1995, Pages 32-34