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A pneumatic pipe bursting system saved
time and money during repair of pipeline infrastructure at McChord
Air Force Base
 Replacement
of an aging pipeline at McChord Air Force Base (AFB), Tacoma,
Washington, was made simple when Seattle-based Pape & Sons
Construction used a pneumatic pipe bursting system to repair
failing concrete sewer pipe.
Through trenchless processes like
pipe bursting are nothing new in Europe, American contractors,
engineers, and municipalities are still discovering the economic
and social benefits of these tools.
McChord expressed interest in using
non-traditional methods such as trenchless technology for the
repair.
A Trenchless
Solution
Pape & Sons investigated the use of
pipe bursting. The McChord job had all the right components:
tree root intrusion in 30-year-old concrete duct, difficult
soil to excavate, close proximity to housing, and extensive
surface structure such as brick divider walls and sidewalks.
The utility contractor sorted through
sales information, real-world results, and interviewed more
than 20 equipment manufacturers, contractors and pipe suppliers
before deciding to go with a pipe bursting system.
A Grundocrack pneumatic pipe bursting
system from TT Technologies, Aurora, Ill., and the model PCZ
180 7-inch tool was ordered for the pipe rehabilitation.
The
Pipe Bursting Process
The pipe bursting process incorporates
preparation of an entry pit at one end of the failed pipe section
where a pneumatic pipe bursting tool and expander are positioned
at the pipe opening. A steel cable emanating from a winch located
at the exit point is attached to the head of the tool. The winch
provides constant tension, helping to guide the tool. The bursting
tool is then launched directly into the old pipe.
The combined effect of the percussive
action of the pneumatic tool and constant tension from the winch
enables the tool to effectively burst through the decayed pipe.
The expander ensures that all pipe fragments are safely compacted
into the surrounding soil and out of the way of the new pipe.
Attached to the back of the tool, the new polyethylene (PE)
pipe follows into the bore. Because an expander is selected
with the outside diameter of the new pipe in mind, a tight fit
is guaranteed.
Specifically, the project involved
replacing 4,900 feet of 6-inch concrete duct with 8-inch SDR
21 high-density PE (HDPE) pipe. The flexural qualities of PE
pipe enhanced the pipe bursting process. The existing concrete
duct was laid in 3.5-feet sections about 30 years ago. Runs
of 100 feet to 325 feet were encountered for the replacement.
The project was actually started by using a dig-in process,
but then bursting took over.
"We were able to accomplish just
one run in 2 to 3 days with the dig-in process. With the bursting
method, we were able to do two runs per day," said Dick Harrod,
a project manager for the contractor.
Pipe Bursting
Saves Money
Pipe bursting opens new windows of opportunities
for improving infrastructure, because trench-and-replace construction
can be so expensive that repairs are often put-off. The failing
pipe then continues to further corrode, demanding the time and
expense of more frequent cleanings.
 Positive
social factors are a key benefit in using pipe bursting. It
allows highway traffic to flow as pipe is installed beneath
pavement, and leaves yards, trees, and gardens intact when replacing
lateral connections.
Because bursting takes less time
to perform than open cutting, it requires minimal disruption
to the public, reduces restoration costs, and generates greater
savings for the owning company, Harrod said.
In the coming months, 13,000 feet
of deteriorating concrete pipe in Mansfield, Washington, will
be rehabilitated. Because of very flat terrain, Mansfield's
present system has developed slow-flow characteristics that
have been contributed to deterioration of joints in the 8-inch
and 10-inch concrete pipe system.
Pipe bursting is expected to be the
method of choice for that replacement, and because of its outstanding
flow properties, HDPE pipe will take care of the slow-flow problem.
Based on the original budget specifying
the trench-and-replace method, the entire trenchless rehabilitation
project will save Mansfield an estimated $350,000.
Pipeline Digest, September
1995, Pages 23-25
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