by Jim Johnson
A $2 million price tag to trench and
replace a crushed storm drain on their campus was out of the question,
according to facility officials at the University of Virginia,
Charlottesville. The sewer replacement needed to be economical
while providing minimal surface disruption.
 A
stretch of 650 ft of emergency storm drain was crumbling from
too much weight. The original storm drain was installed in the
late 1930s, in what was then a ravine. As the university grew
over the decades, more and more fill was deposited into this gully.
The 50-year-old pipe was now buried as deep as 41 ft, beneath
tons of dirt and rock.
The situation came to a head when the
university could not secure an occupancy permit from the state
of Virginia Division of Water Resources for a new $20 million
chemistry building and adjacent science building until the crumbling
storm drain was repaired.
With nearly $40 million in real estate
potentially sitting idle, the university needed the replacement
to be done quickly and economically. Peter Drenan, senior project
manager for facility management at U of VA, Charlottesville, started
researching alternative methods to trench and replace. Drenan
wanted to find a pipe replacement or rehabilitation method that
incorporated positive social factors and was economical.
Drenan first looked into pipe jacking
and found the process to be too costly. It also would have demanded
digging four to six pits. These would have meant the removal of
mature trees and historic structures. The method also requires
the installation of a double wall pipe, which was in excess of
what the replacement entailed.
Other methods discussed were microtunneling
and sliplining. Microtunneling was determined also to be too expensive,
and sliplining, although affordable, could not meet all of Drenan's
criteria. He stated that because the old pipe had become disjointed,
pipe lining could do nothing to align it. What's more, the lining
would not enhance the strength of the crumbling clay pipe. He
then remembered reading about pipe bursting in Trenchless Technology
and decided to contact manufacturers for information.
TT Technologies, Inc., Aurora, IL,
manufacturers of the Grundocrack pneumatic pipe bursting and replacement
systems, provided Drenan with product information and a list of
contractors.
Drenan then contacted several of these
contractors, including Atlantic Coast Contractors, Inc. (ACC)
of Charlotte, NC. ACC is a general contractor that has a background
in new installation and rehabilitation of utilities, including
water, sewer, gas, and storm drains lines. Upon the university's
request, ACC went to work preparing a bid that specified pipe
bursting.
The bid from ACC, using the pipe bursting
method, came in at a fraction of the original $2 million trench
and replace cost estimate. This trenchless process also provided
for the alignment of the line without disrupting mature trees
and historic structures. ACC was awarded the Emergency Storm Drain
Replacement at Scott Stadium East Parking Lot contract on March
3, 1995.
In order to meet the &substantially
complete& deadline of May 12, ACC brought in a team of experts.
TT Technologies' regional manager Eddie Ward provided preconstruction
advice regarding site preparation. J.P. McElvenny Co., Exton,
PA, the pipe supplier, offered PE pipe recommendations and filled
an important last-minute pipe fitting order. Baroid Industrial
Drilling Product's Joe Dobry provided technical support on the
use of the pipe lubricants, and TT's Mike Schwager rendered field
support.
The job was to burst existing clay pipe,
as large as 24-in. OD, and upsize to 28-in. SDR-11 Plexco HDPE
pipe. This would require using a 30-in. expander to create enough
room for the pipe, which has a 34-in. OD. A burst of this nature
had not previously been attempted.
Concerns existed that this particular
pipe bursting application was still theoretical, especially when
upsizing that large a pipe within a deep, crumbling line. After
viewing internal footage of the drain, ACC president John Butler
said, &The video also showed where two boulders had penetrated
the pipe.&
With these and other obstacles looming,
the combined effect of the pneumatic tool and the constant tension
provided by the winch would prove to be more than sufficient.
This is what Schwager, TTÕs on-site manufacturer's rep,
was banking on.
ACC crews arrived in mid-April to begin
preparing the entry and exit pits. This proved to be the most
time consuming aspect of the entire project. Plans were made to
ensure the success of the burst. Another task was to prepare a
back-up plan. In the chance that the burst was not successful,
Butler had made provisions for trenching and emergency bypass
pumping.
&We all agreed to do it right,& said
Drenan, adding, &We wanted to minimize the change of failure.&
This included the service of equipment, using new hoses, and taking
the time necessary to make certain that every component was prepared
to the fullest extent.
The failing storm drain ran between
two parking lots which were separated by the filled-in ravine.
The entry area was adjacent to a hillside stairway, from which
passers-by could get a bird's-eye view of the tool as it waited
for installation. Behind it rested the PE pipe, snaking it's way
around the side of the parking lot into a wooded area.
 The
job was divided into two bursts. The first burst was slated to
be 400 ft with the second at 240 ft. The tool selected by ACC
was the TT Technologies Goliath pneumatic pipe bursting tool.
ACC was experienced and licensed in the art of pipe bursting,
owning a Grundocrack Gigant machine for over two years. This job,
however, required the rental of the more powerful tool.
The 18-in. diameter Goliath tool was
fitted with a 30-in. rear expander to facilitate the pipe upsizing.
Fitted to the rear of the expander was the PE pipe. A short segment
of PE is threaded into the expander, with the full length of pipe
then fused to that segment.
Near the point of entry stood a bentonite
mixing machine, a very important system for the successful completion
of bursts of this magnitude because it lubricates the exterior
of the tool and PE pipe. This reduces the majority of the friction
that occurs during installation.
At the exit end, a 20-ton Grundowinch
was positioned to provide constant tension to the tool. A steel
cable was attached to the pulling eye at the head of the Goliath,
pulling and guiding the assembly all the way to the exit pit once
the job was started.
The first burst was scheduled to take
place on Monday, April 24, but had to be delayed because of the
threat of heavy rains. Drenan required that the 48-hour forecast
be dry in order to proceed with the burst. The burst was finally
started first thing the following day.
This 400-ft run was shot at an average
depth of 25 ft. At first it was slow going, proceeding at a rate
of about 4 to 6 inches per minute--not an encouraging sign to
the contractor. If the tool were to stop, it could result in extensive
efforts to recover it and complete the remaining pipe installation.
Not long after the start of the burst,
the tool's progress began to accelerate to a rate of several feet
per minute. It was expected that the burst would proceed somewhat
slowly, simply because of the dead weight of the 400 ft of pipe.
Schwager estimated the total weight of the tool, expander, and
pipe at 49,000 lbs!
 The
initial drag was attributed to the long length of pipe curving
through the parking lot at the beginning of the installation.
The further the pipe was pulled in, the more it straightened,
eliminating the effect. Butler also credited the increased use
of bentonite for hastening the installation.
This meant that the 400-ft burst was
completed in less than 5 1/2 hours. The second burst was also
completed rapidly, taking just under three hours for the final
240 ft of the job. The combined bursting time for the entire project
was about eight hours. The total project ended up substantially
ahead of schedule and on budget.
&The tool worked to our expectations
and the job was a tremendous success,& declared Greg Williams,
ACC project manager.
ACC makes it a priority to be involved
in the continuing education of new technologies in order to keep
up in today's market. With the successful installation of the
university's storm drain to its credit, ACC looks forward to even
more projects where pipe bursting can be presented as an economical
alternative.
What was once a theory, is now practice. In fact, it's academic.
Jim Johnson is a writer for Lime Valley Advertising, Mankato,
MN. Grundocrack tools are protected by British Gas patents.
Trenchless
Technology, August 1995, Pages 60-62
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