Replacing AC pipe via HDD, PVC.
"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."
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 math 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.
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."
The city hired Olympia contractor Wiseman Utilities Inc., to install approximately 3,400 feet of eight-inch pipe and connect all services along the route. Working with a crew of six, the contractor dug potholes and marked the location and elevation of utility lines underground. The crew began boring through compacted brown sands with compacted glacial cobbles at depths of seven to 9 feet to get around existing utilities. According to Wiseman Utilities owner Kevin Wiseman, attempting this in an open-trench installation would have been more complicated and less safe than it was with HDD.
"When you're trenching nine feet deep, you've got shoring boxes and the conflicts of existing utility lines," Wiseman says. "We were boring three feet away from the existing main, which had 31/2 feet of cover above it. AC pipe has more narrow bells than other materials and when you're excavating beside it, especially in sandy soils, it tends to gradually slide off. Once a joint in the old AC pipe becomes exposed, all you need is a few more feet of shifting before the resulting pressure blows the joint apart, causing a main break and safety hazards. HDD definitely offered the path of the least resistance."
Among the equipment Wiseman Utilities used were a Vermeer 36x50 directional drill (36,000 pounds pullback, 5,000 foot pounds radial torque), a Kenworth T800 flatbed truck pulling a Vermeer 750 mud vacuum trailer, three Case 580 backhoes, one Samsung 130 excavator, a Caterpillar 303 mini excavator and two Kenworth T800 dump trucks, and a Vactor 2100 Series PD truck.
In reaching the 3,400 foot length of the pipeline, the crew made a series of bores, ranging from 450 to 500 feet, based on the distance between intersections, where valves and hydrants would later be tied in. Pipe was pulled in behind a 16-inch Geological Boring Company back reamer, assembled in 20-foot lengths during the pullback process. Boring and pullback ran smoothly, and the easy assembly of the Certa-Lok pipe helped the crew to work faster.
For this project, Wiseman Utilities purchased a special tool from CertainTeed for fabricating spline grooves and beveling pipe on-site. They also purchased an assembly tool from Pro-Pipe Solutions called the Eagle Claw. This helped the pipe assembly to run even more smoothly, as it helped the crew to pull the collars in more evenly and line up the pipe string correctly. The biggest challenge of the project came after the pipe was installed, when the crew disconnected the existing lateral mains from the existing eight-inch AC main and reconnected them to the new main at street intersections.
"Doing the interties with the existing water mains in the intersection was challenging because the existing mains had been placed at all elevations and at different times of history," Wiseman says. "As for pipe, it was a mixed bag of materials, from steel and ductile iron to AC and PVC. This made the process more labor-intensive. The crossover work was done at night to minimize service disruptions to the affected businesses. We learned after the first crossover to do them on Thursdays so the crew could have the whole weekend to rest up."
As the project moved into winter, the crew also ran into some days of snowy and icy weather, which occasionally stalled the project. The contractor still met its deadline, though, finishing in 45 work days, and the new water main easily passed pressure testing. After it was brought online, the old AC water main was plugged with control density fill and abandoned, per the regulations of the State of Washington Department of Ecology.
Wiseman Utilities received excellent feedback for its work and for keeping disruptions at a minimum.
"It went very well," Wiseman says. "The city and business owners along the project route were very pleased. We only had to close the far right lane of a four-lane boulevard, so the disruption was minimal."
In addition to HDD helping the project run more smoothly and keep down disturbance, it considerably decreased project costs by minimizing the need for road restoration. The city of Olympia was very pleased with all of these results.
"Restoring a road after an open-trench project takes a lot of money and effort," Lu says. "This project came out with less than half of the expense of what it would have cost for us to use open trench because we didn't have to repair the concrete and asphalt or make frontage improvements. We're very happy with the work Wiseman Utilities has done for us. They're very professional, and they know what they're doing."
FOR MORE INFO:
Wiseman Utilities Inc.
(360) 705-0511, www.wisemanutilities.lbu.com
(800) 233-8990, www.certainteed.com/products/ pipe# Vactor
(815) 672-3171, www.vactor.com
(262) 636-6772, www.casece.com
(888) 837-6337, www.vermeer.com
(541) 998-3736, www.propipesolutions.com
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|Title Annotation:||DIRECTIONAL DRILLING|
|Date:||Sep 1, 2012|
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