Replacing AC Pipe Via HDD, PVC

September 2012, Vol. 67 No. 9

In 2011, the city of Olympia, WA, was faced with finding the best replacement pipe material and installation method for an aging asbestos cement (AC) water main.

The main, aged between 50 and 60 years, had experienced three breaks over three years and had yet another during the design phase of the replacement project, increasing its total footage. Adding to the predicament was the pipe’s location underneath Martin Way, one of the city’s busiest streets, in a district with multiple businesses and multifamily developments.

“We originally intended to use open trench for the project, since it is traditional and more of our local contractors would be able to bid on it,” says Zheng Lu, project engineer for the city of Olympia. “However, the original AC main was underneath a high-traffic concrete panel road with asphalt paving, so in an open-trench installation, we would not only have to replace the concrete afterwards, but also significantly restrict traffic during construction. A trenchless installation would only require us to close one of four lanes of traffic.”

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The municipality then looked into various trenchless installation methods, including cured-in-place pipe (CIPP) rehabilitation technology, static pipe bursting and horizontal directional drilling (HDD). For this project, CIPP proved too expensive and would require the original water main to be shut down during the project. Pipe bursting, too, was passed over, due to the environmental sensitivities about AC pipe. Directionally boring adjacent to the existing main, installing new pipe and disconnecting and abandoning the old one, was decided as the best application for this project.

PVC
For the replacement pipe, the Olympia specified CertainTeed Certa-Lok C-900/RJ restrained-joint PVC pipe, which was the best fit for its municipal maintenance crew.

“Our maintenance crew already had the proper tools and fittings in stock for PVC and ductile iron pipe, but didn’t have the fusion equipment or parts for HDPE pipe,” Lu says. “They asked us if we could use PVC on the project instead of HDPE. We found that Certa-Lok restrained-joint PVC pipe was widely used for potable water applications, so that was our choice.”