|
by Jim
Schill
|
The
City of St. Louis Park, MN replaced approximately
1,700 feet of 6-inch cast iron water main with 8-inch
HDPE through static pipe bursting. The trenchless
application kept disruption to a minimum in a highly
traveled area of the city.
|
The
city of St Louis Park, MN is experiencing significant
commercial and residential redevelopment. As a result,
the Public Works Department is always looking for cost-effective
means for upgrading utility infrastructure. A recent
water main replacement project gave city officials their
first look at trenchless pipe bursting. The results were
impressive and more pipe bursting work could be in the
city’s future.
Statistics
The
city of St. Louis Park covers 10.8 square miles just west
of Minneapolis and is home to over 44,000 residents. The
city’s water system is comprised of over 140 miles
of water main, six treatment plants, three water towers
and four reservoirs. Over two billion gallons of water flow
through the city’s system each year and 6.5 million
gallons of water are used on an average day.
The planned development of a $115 million multi-use commercial
and residential complex threatened to tax the area’s
aging water system beyond its capacity. According to St.
Louis Park City Engineer, Maria Hagen, the location of
the existing water main prompted the city to explore trenchless
construction methods rather than traditional open cut.
Ultimately static pipe bursting was specified for the project.
Hagen said, "Trenchless pipe bursting was a good application
for this area because of a combination of factors. We had
a lot of traffic so we wanted to get the job done quickly
with as little disruption as possible. Plus, the street
was paved in concrete. Removing and replacing the concrete
would not only have been time consuming and disruptive,
it would have been very expensive as well." The close
proximity of a natural gas main to the water main also
made trenchless pipe bursting a preferable replacement
option.
Utility contractor Tjader & Highstrom, New Richmond,
WI was contracted for the project. The Grundoburst 800G
static pipe bursting system from trenchless equipment manufacturer
TT Technologies, Aurora, Ill. was utilized.
|
During
the static bursting process bladed rollers are pulled
through an existing line by a hydraulic bursting unit.
The bladed rollers split the host pipe. A bursting
head and expander displaced the fragmented host pipe
in to the surrounding soil while the new HDPE is pulled
in simultaneously.
|
Static Pipe
Bursting
Over the
last several years static pipe bursting has been gaining
popularity and favor among public works officials, engineers
and pipe replacement contractors. During the static bursting
process, a special bladed roller is pulled through the
existing line by a hydraulically powered bursting unit.
As the bladed rollers are pulled through, they split the
host pipe. An expander attached to the rollers forces the
fragmented pipe into the surrounding soil while simultaneously
pulling in the new pipe, usually High-Density Polyethylene
(HDPE).
The specially designed bladed rollers are essential to the
bursting process. The blades actually split the host pipe
instead of ripping or tearing it. This makes the process
very clean and prevents potential damage to the product
pipe. It also makes bursting ductile iron and steel pipes
possible, a first for pipe bursting equipment.
The Project
The
water main replacement project took place under the heavily
traveled Excelsior Boulevard, which carries over 21,000
vehicles per day. Plans called for the replacement of approximately
1,700 feet of existing 6-inch cast iron water main with
8-inch HDPE. The project was divided into four sections
each ranging between 410 and 475 feet.
Exit and launch pits were excavated at the beginning and
end of each pipe bursting run. A 6-inch temporary bypass
was established to provide water service to six area businesses
during the project. With the exception of one line sweep
that did not appear on any records and required excavation,
the static bursting equipment had no difficulty with the
6-inch cast iron pipe. Bursting went very quickly with times
ranging from one hour and 15 minutes to three hours per
run.
Hagen said, "The project was innovative for several
reasons. First, the pipe bursting method is innovative in
and of itself. Second, this was the first static pipe bursting
project for a water main in the State of Minnesota. Everyone
was very pleased with the results. However, when contemplating
trenchless projects, very accurate as-built plans, both
of City and private utilities, are needed to minimize interruptions
and conflicts with other infrastructure." Hagen said
the city is looking at other projects where static pipe
bursting could be used in the future.
|
