Many cities around the country are faced with the problem of trying to service an ever-increasing population on water and sewer systems installed 50 to 70 years ago. Many systems are simply undersized, while others have deteriorated beyond the point of adequate function.The prospect of replacing these systems raises additional questions about how the system should be replaced. In order to avoid costly restoration and social disruption, many cities are turning to trenchless methods of pipe replacement, specifically trenchless pipe bursting. The city of Belton, MO is realizing the social and monetary benefits of trenchless water main replacement through pneumatic pipe bursting.
The city of Belton is growing. The current population of 23,000 is up significantly from 18,000 just ten years ago. The city’s existing cast iron water system was installed in the late 1940s and early 1950s. This summer, many residents experienced problems with diminished system pressure and rusty water. In addition, new home starts and subdivisions promise to put more of strain on the already under capacitated system.According Belton Public Works Supervisor Cliff Fain initial problems began occurring after the replacement of one of the city’s primary main lines. Fain said, “In 1995 we installed and re-routed a 16-inch mainline to replace an outdated 6-inch main. After bringing that main into service, we began experiencing problems with the rest of the existing system.”The increased pressure from the new 16-inch line was putting more stress on the old cast iron system than it could handle. Over the last several years the city experienced multiple water line breaks as well as significant levels of seepage. According to Fain, the dilapidated cast iron lines were restricted by nearly 45 percent from corrosion and sediment build up.
The city initially planned to redesign, open cut and replace most of the system, as well as the service connections. The timing of resident complaints prompted the city to expedite the project and look for an alternative replacement method. Fain said, “We had done some pipe bursting in our sewer systems with Wiedenmann & Godfrey Construction. After the water service problems we experienced, I asked them if they ever anticipated doing any pipe bursting for water. In a matter of two or three weeks later, we had a plan.”Wiedenmann & Godfrey Construction, Inc., Belton, MO, was awarded the project to replace 4,500 feet of 4-inch cast iron water main to 8-inch High Density Polyethylene pipe (HDPE) through pipe bursting this past July.
According to Wiedenmann & Godfrey President Jerry Wiedenmann, the pipe bursting process is simple yet very effective. He said, “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. Depending on the specific situation, the tool is equipped with an expander that displaces the host pipe fragments and makes room for the new pipe. As the tool makes its way through the host pipe, it simultaneously pulls in the new pipe, usually HDPE.” For this particular job, Wiedenmann used a Grundocrack Hercules pipe bursting tool with a 10-inch rear expander and a 10-ton constant tension Grundowinch from trenchless equipment manufacturer TT Technologies, Aurora, IL.From July until November 2000, the Wiedenmann & Godfrey crew divided the 4,500-foot job into 600- to 700-foot sections and proceeded to burst, replace and upsize the 4-inch cast iron mains with 8-inch HDPE. In addition, crews replaced water services along the main by utilizing a Grundomat trenchless boring tool. Services were tied into the main using electro-fusion saddles. Wiedenmann & Godfrey tested and chlorinated each new section of pipe before putting it into service.
According to Fain, the money originally budgeted for design work on the open cut project played a much different role in the bursting project. He said, “Originally we budgeted for the design work but ended up using that money to replace pipe through bursting. Because pipe bursting follows the path of the existing line, we didn’t need to hire an engineering firm and draw out an elaborate design. We generated the design in-house and saved a lot of time and money.”In addition, the city was able to avoid traffic disruption and landscape restoration by employing the trenchless replacement method. Fain foresees more bursting for Belton in the future. He said, “If we were to replace the area we’re looking at right now, it would total approximately 32,000 feet of 4-inch and 6-inch cast iron. I would anticipate as much as two-thirds of that would be replaced by pipe bursting.”
by Jim Schill
American City & County, December 2000