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Replacing AC Pipe Via HDD, PVC
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 3½ 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.