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The
Louisville Water Company crews used a Grundoburst
400G trenchless static pipe bursting system to replace
900 feet of 6-inch cast iron water main with 8-inch
HDPE. The static system allowed the water utility
to replace the pipe while minimizing disruption and
costly restoration.
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The
city of Louisville, KY is taking an aggressive approach
to upgrading and replacing deteriorating water mains.
The city’s
water system, operated by the Louisville Water Company
(LWC), consists of over 3,200 miles of water mains and
handles 127 million gallons of water per day. Louisville
Water serves over 900,000 people through its 240,000
domestic, commercial industrial, retail and wholesale
customer accounts.
A majority of the cast iron system targeted for replacement was installed in
the 1930s and before. The LWC has been systematically replacing these deteriorating
water mains for over two decades. The utility has turned to pneumatic pipe bursting
as one solution to its problem. The method has allowed the city to replace aging
sewer mains effectively and efficiently while minimizing social disruption and
lowering restoration costs.
Main
Replacement and Rehabilitation Program
The
Louisville Water Company’s main replacement and rehabilitation
program (MRRP) targets approximately 25 miles of pipe annually
for replacement or rehabilitation. Officials outline projects
for the program that will take place over a two-year period.
Projects are selected based on a pipe evaluation model
(PEM).
LWC Program Manager Keith Coombs explained, “The
PEM is set up to look at 23 different criteria, group in
four different categories. They include geography and location,
hydraulics, maintenance, which encompasses break history,
and quality of service. By evaluating mains based on the
different criteria in each category we determine which
mains are good candidates for the replacement.”
Beginning in 1976 with a modest budget of $200,000, the program has grown to
a budget of over $8 million, representing approximately 15 percent of the annual
capital improvement budget.
While much of the replacement that is done is completed through traditional open-cut
methods, the LWC is always looking for new and more efficient methods of construction.
Trenchless technology, specifically trenchless pipe bursting is one method that
has gained favor with the water utility.
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Trenchless
pipe bursting plays a key role
in the LWC’s Main Replacement
and Rehabilitation Program.
Main replacements under sensitive
areas like streets and roadways
and difficult locations like
parks and sidewalks are prime
candidates for bursting.
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Pipe Bursting
Pneumatic
and static pipe bursting equipment are common. Pneumatic
tools are typically used for fracturable pipes like clay
and concrete. The emergence of new static bursting equipment
over the past several years has made the bursting of ductile
iron and steel pipes and repair sleeves possible. The LWC
has utilized both methods in its replacement program.
During pneumatic pipe bursting, the pipe bursting tool is guided through a fracturable
host pipe by a constant tension winch. As the tool travels through the pipe,
its percussive action effectively breaks apart the old pipe and displaces the
fragments into the surrounding soil.
Static systems, unlike pneumatic bursting tools, do not incorporate percussive
action to break apart host pipes. Static bursting systems utilize a configuration
of specially designed bladed rollers and an expander to split the host pipe and
force the fragmented pipe into the surrounding soil.
The process is simple. After the hydraulic bursting unit is positioned in the
exit pit, bursting rods are installed through the host pipe and into the launch
pit. Once at the launch pit, crewmembers attach the bladed cutting wheels, bursting
head, expander and new High-Density Polyethylene (HDPE) to the bursting rods.
The entire configuration is then pulled back through the host pipe by the bursting
unit. The bladed cutting wheels split the host pipe. The bursting head and expander
displace the burst host pipe while the new HDPE is pulled in simultaneously.
The unique system allows crews to chlorinate water mains before installing them
and makes bursting ductile iron and steel pipes possible.
Since 1999, the LWC has replaced almost 10,000 feet of pipe through static and
pneumatic pipe bursting methods. While the municipality does not own any bursting
equipment, it does perform bursting projects with in-house crews and contracts
for bursting projects with qualified pipe bursting contractors.
Recent
Project
LWC in-house crews recently replaced 900 feet of 6-inch
cast iron pipe with 8-inch HDPE through static pipe bursting.
With technical support provided by trenchless equipment
manufacturer TT Technologies, Aurora, Ill., the project
was subdivided into two sections.
The first 400-foot section of 6-inch cast iron main ran
under a local park. The second section of approximately
500 feet ran under a frequently traveled roadway. The crews
placed a 400G Grundoburst static pipe bursting system in
the exit pit at the end of the first run. After installing
the bursting rods, the crew pulled back the bladed rollers
and 400 feet of 8-inch HDPE, replacing the existing 6-inch
cast iron.
For the second burst, the static machine was positioned
in the exit pit at the end of the second run. Bursting
times for this section, as well as other sections, generally
ranged between two and three hours.
According to Coombs bursting was a good option for this
project and crews took to the method well. He said, “The
location of the project made the pipe bursting method particularly
attractive. We were not interested in trenching through
the park and open cutting the roadway would have created
many problems with traffic and congestion. With a minimal
amount of training and some technical support our crews
were able to get a handle on the bursting method quickly.
And the results were very positive.”
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