Big Burst in the Sunshine State

PUCC Takes On 36-inch Force Main In Tallahassee
October 2010 Vol. 65 No. 10

A problem was encountered at the start of the pilot project. Excavation of the bursting head revealed that the 36-inch DIPS expander’s one-inch cutting blades were too small to cut through the host pipe’s couplings. Crews welded three larger 3-inch cutting blades to the expander at the 10, 12 and 2 o’clock positions. Following this adjustment, the pilot continued successfully until completed with no evidence of road heave.

The burst was completed in 90 minutes at an average bursting rate of three feet per minute. All parties were pleased with the successful outcome of the pilot and it was determined that the remaining length of project would be completed through pneumatic pipebursting.

Equipment considerations
Despite the attention that static pipebursting has receive in recent years, pneumatic pipe bursting continues to be a workhorse option for trenchless pipe replacement. And, in this case, it proved to be a significantly capable option considering the challenging nature of the project. For the Tallahassee project, the pneumatic system was chosen because of the impact force the method provides and because the method was successfully employed for bursting a similar type of pipe in California.

During pneumatic pipebursting, the 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.

With the use of expanders, one tool can be used to burst several different size host pipes and replace them with new HDPE of the same size or larger. The rear expander configuration provides several key advantages, one of which is that it allows the use of bentonite in conditions that warrant fluid use.

Tool and expander selection is affected by various factors including host pipe type, depth and profile, jobsite layout, burst length, soil conditions and more. Upsizing is also a major consideration in tool expander selection. Some extremely large upsizes in the 120-125 percent range have been successfully completed through bursting. These bursts are typically categorized as experimental, although quite a few have been completed successfully. The 25-50 percent upsize is much more common, but is still challenging. Upsizes between zero and 25 percent are considered common.

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