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.
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.
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.”
American City and County, November 2003