Louisville Water Company, Louisville, KY provides over 120 million gallons of water per day to over 240,000 residential, commercial and industrial customers throughout the greater Louisville area. Recently the water utility company began a major water main rehabilitation project to replace sections of deteriorating and tuberculated cast iron water main through pipe bursting.
To complete the project, pipeline contractor Southern Pipeline Construction Company, Louisville, KY was contracted to burst and replace several thousand feet of 4-inch and 6-inch cast iron pipe using the Grundoburst 400G static pipe bursting system from associate NUCA member TT Technologies, Aurora, IL.
Several years earlier, Southern Pipeline, a multi-facetted pipeline contractor with almost 50 years of experience, performed a pilot project for Louisville water using pneumatic bursting equipment. Static equipment was chosen for this project.
Southern Pipeline CEO Stephen Mullins said, “Basically, they [Louisville Water] wanted to do another pilot project, this time with static bursting. Everyone was very impressed with pneumatic bursting and this was an opportunity to demonstrate the capabilities of the static system. Many sections of the bursting took place under streets, parkways and highly landscaped areas. All these areas benefited from the trenchless application.” In addition the method offered an opportunity to attempt to chlorinate the lines before installing them. This was some of the first pre-chlorination bursting work performed in North America.
The Static Bursting Process
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 Grundoburst 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 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.
For the Louisville Water Company project, Southern Pipeline burst and replaced 4-inch and 6-inch cast iron with 6-inch High-Density Polyethylene (HDPE) pipe. The project was subdivided into sections. According to Mullins, the first section was representative of the total project.
He said, “The first section was under pavement on 24th Street. The 481-foot, 4-inch cast iron main needed to be replaced with 6-inch HDPE. We divided the run in half and placed the Grundoburst in the pit at the middle. The first burst traveled north to south. After installing the bursting rods, we pulled back the bladed rollers and 230 feet of 6-inch HDPE.”
For the second burst, the Southern Pipeline crew used the same pit, but turned the Grundoburst around 180 degrees in order to burst from the other direction, south to north. Bursting times for this section, as well as other sections, ranged between two and three hours.
In addition, Southern Pipeline’s initial attempts at pre-chlorinating the HDPE were met with promising results. Mullins said, “Our pre-chlorination efforts during this pilot project were hampered at first because of leak in the pulling head section of the pipe, the point where we actually attached the pipe to the pulling head. We installed an extra seal weld on the inside of the pipe, and on subsequent tries, pre-chlorination proved effective and past the testing.”
According to Mullins everyone involved with the project was pleased with the results. Southern Pipeline is currently working on other static bursting projects and Mullins anticipates more static bursting in the future.
by Jim Schill
NUCA, January 2002