- ENGINEERING INFO
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The City of Fairfax owns and operates the Goose Creek Water Treatment Plant, which is located north and west of the City in Loudoun County. The treatment and distribution network was built in 1961 to replace wells that were experiencing water table depletion, and is approaching 50 years of age. As a responsible potable water purveyor, Fairfax City, under Utility Director Rick Thoesen, performed an asset management survey on the 22-mile long potable water main that transports water from the treatment plant to the service area in and around the City. Most of the 24-inch PCCP line was in good shape, but there appeared to be a weakened section of pipe located under the Dulles Toll Road in Fairfax County. Rick Thoesen noted, "Normally, our agency would dig and repair such a location as part of our ongoing maintenance, but it became readily apparent that the section in distress was just not accessible to our crews. Instead, we knew we had to become creative to effect a fix."
The City selected Whitman Requardt & Associates to investigate and design the rehabilitation of about 500 LF of 24-inch PCCP under the Toll Road. Under consideration were sliplining with Fusible PVC® pipe or HDPE, or a close-fit, pressure-rated, cured-in-place pipe (CIPP). Ultimately, the pressure-rated CIPP was deemed experimental, and the HDPE pipe required too thick of a wall to allow for reasonable flow area through the rehabilitation section. WRA designer Dean Westman remarked, "Fusible C-905® pipe was the only pipe material that combined the highest structural integrity with the greatest hydraulic capacity for this particular application. The sliplining process was smooth and efficient and we are confident that the repair has restored many more years of service to the pipeline."
The project was contracted through a public bidding process, resulting in a low bidder inexperienced with Fusible PVC® pipe and reluctant to build the chosen design. The low bidder instead proposed an open-cut route under the Toll Road. That approach was ultimately rejected by Fairfax City due to multiple permitting and construction difficulties. Anchor Construction then proceeded with the rehabilitation in May 2012. With guidance from engineering inspectors and Underground Solutions' construction manager, the work went smoothly and the pipeline was back in service after about three weeks.
|Pipeline Details and Project Summary|
|Project:||Water Main Rehabilitation|
|Pipe Size:||20" in 24" PCCP Host Pipe|
|Pressure Test:||150 psi|
|Owner:||City of Fairfax, VA|
|Engineer:||Whitman, Requardt & Associates|
|Site conditions allowed for entire 520 LF of 20-inch Fusible PVC® pipe to be fused and laid out on the north side of the Dulles Toll Road. Fused Joints were externally debeaded to assist with smooth entry and pullback. Subcontractor, Midas Utility, Inc., used TT Technologies static pipe bursting equipment to apply the necessary pulling force.||Project documents required pipe to be tested to 150 psi after lining, but before grouting. A grouting subcontractor then utilized a cement/fly ash/sand grout with a foaming agent to fill the annular space from one end to the other. Test water remained in the pipe as a heat sink for the heat of hydration and an anti-buoyancy measure.||The final step in the process involved making the connection back to the host PCCP with standard ductile iron mechanical joint fittings. Visual inspection after the line was placed in service proved the connection sound and leak-proof.|