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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.
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.
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.
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
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