by Jim Schill
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The
MichCon crews utilize a “keyhole” installation
technique for installing new service lines. The technique
creates minimal disruption and involves coring a
small hole in the street to access the main.
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Finding better
and more efficient and effective ways of utilizing underground
construction technology is a hallmark of the gas utility
industry. In fact, gas utilities are very much responsible
for the development and refinement of many of the trenchless
construction methods utilized today.
Like most large gas utilities around the country MichCon,
Detroit, Mich. (a subsidiary of DTE Energy), has roots
that go back well over 100 years. Many things have changed
since the company’s beginnings and in order to
remain competitive MichCon has had to meet and exceed
the needs of its customers. One way it has been able
to achieve a level of high customer service is through
the construction techniques that minimize disruption
and increase efficiency for service installations and
replacement.
According to MichCon Project Supervisor Michael Arioli
cost and customer service have driven them from conventional
construction techniques to trenchless methods. He said, “We are very focused on customer service, as well as efficiency.
By utilizing trenchless technology we can often achieve both goals at the same
time. We’re keeping disruption to a minimum. We don’t have to trench
through peoples’ yards, driveways and sidewalks. We’re also keeping
disruption to the streets and roads down which helps traffic. And finally, we’re
saving time and money on each project.”
New service installations and service line upgrades are
two areas where trenchless technology has had a big impact
at MichCon. Crews are using a “keyhole” technique
to limit disruption and save restoration costs. The crews use 1.75-inch and 2-inch
diameter Grundomat piercing tools from trenchless equipment manufacturer TT Technologies,
Aurora, Ill on a daily basis and the results are impressive.
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The
extremely accurate Grundomat piercing tool makes
the keyhole process possible. Crews shoot the tool
from the house to an 18-inch diameter hole, usually
in the street at distances averaging 50 feet.
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Utility
Stats
MichCon Gas is
one of the nation’s largest and oldest providers
of natural gas, having served the city of Detroit and surrounding
areas for over 150 years. Currently the utility supplies
natural gas to approximately 1.3 million families and businesses
in over 500 communities throughout Michigan. They maintain
over 18,900 miles of natural gas pipeline and have the
ability to store 130 billion cubic feet of natural gas.
Service installations keep MichCon Gas crews particularly busy. With over 150
service installations per month (either new service, upgrade or rehab/replacement)
how maintenance crews approach them can have a significant effect on time and
money. Arioli says the company has looked at many different construction techniques
for facilitating these installations.
He said, “The cost of doing work conventionally is increased dramatically
by the cost of excavation. We looked at several trenchless options including
directional drilling units, but for this work we found them to be cost and time
prohibitive. By utilizing keyhole technology with trenchless piercing tools the
same work can be accomplished for a fraction of the cost. It reduces the cost
of open cut restoration by over 500 percent.”
While new service or rehab/replacement installation is common, Arioli has
seen a consumer demand trend in his area that began after the blackout in the
summer of 2003. Since that event, customers have been requesting larger services
to accommodate gas-powered generators in the event of another electrical power
loss. The gas-powered generators require a 1 1/8-inch service to operate, much
larger than the area’s 1/2- to 3/4-inch standard services.
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The
Grundomat’s reciprocating stepped cone chisel
head moves independently from the main casing,
powering through obstacles and creating a pilot
bore for the main tool body to follow. This design
ensures the tool’s accuracy.
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Through
the Keyhole
As the name
implies, keyhole installations utilize small excavations.
While each installation is different, 50 feet is the
average length. Crews begin by excavating a small hole
in the road above the main. Arioli explained, “To
excavate the road we use what we call a cookie cutter.
It’s a specially designed coring machine for
concrete and asphalt. We core through the pavement,
asphalt or sidewalk to a depth of two feet and remove
the core. The diameter of the hole is only 18 inches.
Once the coring is complete we vacuum excavate down
to the main, usually four or five feet deep.”
Meanwhile at the house, another minimal excavation is performed to allow the
launch of the piercing tool. According Arioli the launch pit is typically 4 inches
wide, 26 inches long and 14 inches deep. From there the piercing tool is launched
to the 18-inch diameter core (keyhole) in the street. Crews position the piercing
tool using a telescopic Grundoscope aiming frame and surveyor stake before launching
in order to ensure that the tool starts out on the proper line and grade. Still,
working with such small targets, the precision and accuracy of the piercing tool
is an absolute must.
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MichCon
performs over 150 service line/keyhole operations
a month. The company dedicates three crews for
fulltime service line installations.
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Accuracy
is Key
The basic
design for the piercing tool is rather simple. The
tool is basically a piston within a casing. Compressed
air moves the piston and the impact of the piston drives
the tool forward. More is needed, however, to achieve
the high level of accuracy necessary to perform the
keyhole work that MichCon gas is performing.
According to TT Technologies Piercing Tool Specialist Brian Mattson, early piercing
tool technology with this basic design was often thought of as unreliable and
because accuracy was an issue. The development of the Grundomat piercing tool
with a reciprocating stepped-cone chisel-head assembly in the 1970s helped change
the way contractors viewed piercing tools.
Mattson said, “The chisel-head assembly really makes the difference when
it comes to accuracy. The assembly is spring-loaded and pushes forward from the
main casing at a rate of approximately nine times per second. This creates a
pilot bore for the Grundomat to follow, ensuring a high degree of accuracy. The
reciprocating spring loaded action and stepped-cone design allow the tool to
power through difficult soils and obstructions without being pushed off course.
While the body of the tool is tight in the ground the head moves independently
like a small jack hammer. Most piercing tools will deflect when hitting an object,
because of the cylindrical head design.”
Piercing tools are used in water, gas, sewer, electrical, CATV and other construction
applications and range in size from as small as 1 3/4 inches in diameter up to
7 inches. Accurate bores at lengths of 50 to 150 feet are common. In addition
to horizontal boring, the tools can be used for other applications like pipe
bursting and pipe ramming.
Pulling
in Pipe
MichCon
crews use 1 3/4-inch and 2-inch piercing tools for keyhole
operations. Once the tool arrives at the 18-inch diameter
core in the sidewalk, street or roadway, crews attach the
new Medium Density Polyethylene (MDPE) service to the front
of the piercing tool. Because the diameter of the keyhole
is so small, the tool cannot be removed through it. Instead,
the new pipe is attached to the front of the tool and the
tool is placed in reverse and backed out to the launch
pit. As the tool is backing out it pulls the MDPE in place.
MichCon dedicates three crews to fulltime keyhole installations. Crews are typically
able to finish two or three installations per day.
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