By Tyler Henning
While City Utilities of Springfield, MO, maintains more than 1,100 miles of water main, an 800-foot section of the main came under scrutiny in 2005. The municipality decided to rehabilitate the questionable 36-inch concrete transmission pipe by sliplining the pipe with 30-inch high-density polyethylene pipe (HDPE).
Sliplining is the process of rehabilitating deteriorating pipe by “slipping” a smaller pipe into an existing, larger pipe. It could be said that Springfield was ahead of the curve, installing one of the largest diameter HDPE potable water pipelines in such a fashion.
“We have been using HDPE for some water projects for a couple of years now,” said Kem Reed, P.E., assistant manager of water engineering for City Utilities. “It has been primarily used in cul-de-sacs and directional drilling applications.”
Before using HDPE, Springfield installed pipe in cul-de-sacs with glued PVC 45- and 22½-degree ells, which created opportunities for leaks and was a time-consuming process.
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The Process
The troubled section of water main was located in the backyards of 10 newly constructed homes. Sliplining the pipe with 30-inch DR 11 HDPE saved money by going underneath the freshly landscaped backyards, avoiding restoration costs. The 800-foot pipe was butt fused together by Poly Pro fusion contractors using a McElroy TracStar 900 fusion machine.
Butt fusion is the process of using heat and pressure to connect polyethylene pipes end to end. After the ends of the pipe are melted with a heater, the pipe ends are pressed together and held under pressure until the melt cools. The resulting fusion joint is proven to be as strong as the pipe itself, requiring no reinforcements.
“With fused joints, the pipe becomes a monolithic structure and has no joint,” said Tom Cravens, owner of Poly Pro. “HDPE has consistently proven itself in problem areas and bores.”
A cap was fused onto the front of the pipeline to prevent anything from entering the pipe during the operation. Entrance and exit pits were established. Bill Davis, owner of Davis Structure and Development Corp. and general contractor for the sliplining operation, decided to employ a pushing method by using a sling around the HDPE pipe that hooked to a backhoe bucket. The pipe was then pushed into the existing pipe until it emerged from the exit pit. Adapters were fused on the ends of the HDPE pipe so that it could be attached to the existing pipe.
“The insertion process took less than an hour and (the HDPE pipe) came out the other end relatively unscathed,” said Reed.
Reed estimated that the choice of HDPE saved the city $60,000, not including the expense that would have been required to refurbish the 10 backyards the line traversed. Manpower hours were also reduced by the speed of the project.
Three years after the initial 2005 slipline operation, Reed said Springfield continues to use directional drilling applications and HDPE for main installations in cul-de-sacs.
“It has given us the experience and trust in HDPE for other projects of a similar nature that might come up,” he said.WW
About the Authors:
Tyler Henning is a public relations specialist for McElroy Manufacturing, Inc. He can be reached at [email protected] or (918) 831-9286.
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