Bursting at the seams
As part of an ongoing water main replacement and rehabilitation program, the Louisville (Ky.) Water Co. (LWC) recently replaced 900 feet of cast iron pipe with high-density polyethylene pipe (HDPE) by using trenchless technology. The method helped the utility replace the 70-year old pipe without digging through a park and a nearby street under which the pipe was situated.
Metropolitan Louisville’s water system, operated by LWC, consists of more than 3,200 miles of water mains and handles 127 million gallons of water per day. LWC serves more than 900,000 people through its 240,000 residential, commercial, industrial, retail and wholesale accounts.
For more than two decades, LWC has been systematically replacing deteriorating cast iron water mains that were installed in the 1930s. Beginning in 1976 with a budget of $200,000, the main replacement program has grown to a budget of more than $8 million, which is approximately 15 percent of LWC’s annual capital improvement budget.
Each year, LWC replaces or rehabilitates about 25 miles of pipe, depending on the results of a pipe evaluation model (PEM). “The PEM is set up to look at 23 different criteria, grouped in four different categories,” says LWC Program Manager Keith Coombs. “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.”
The main that ran under the park and street was tuberculated (meaning corrosion byproducts and minerals were encrusted on the inside of the pipe wall) and, in places, severely deteriorated. Because of the pipes’ condition, the agency was concerned about water quality and fire flow capacity.
In September, LWC crews began replacing the main by dividing the project into two sections. The first 400-foot section of 6-inch cast iron main ran under a park. The second section of approximately 500 feet ran under a frequently traveled roadway.
With technical support and equipment from Aurora, Ill.-based TT Technologies, LWC crews used a static pipe bursting system to break the existing pipe into fragments and install 8-inch HDPE pipe. Working first on the pipe under the park, crews placed a hydraulic bursting unit in a pit at one end of the work site and then pushed rods through the 400 feet of pipe. When the rods reached a pit at the other end, crewmembers attached cutting wheels, a bursting head, an expander and new HDPE pipe to the rods. The bursting unit pulled the rods, cutting wheels, bursting head, expander and HDPE pipe back through the cast iron pipe. The bladed cutting wheels split the cast iron pipe, and the bursting head and expander displaced the fragmented host pipe into the soil while the new HDPE was pulled in place. The process was repeated on the section under the roadway.
“The location of the project made the pipe bursting method particularly attractive,” Coombs says. “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.”
By replacing the 6-inch cast iron pipe with 8-inch HDPE, LWC resolved the water quality issues in the area and improved fire flow capacity. The $40,000 project was completed in three weeks.
