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Pipe Bursting Solves Environmental Issues
A key benefit of the method is reduced excavation requirements, which allows new pipe to be installed in areas where restoration would be costly and disruptive. Pipe bursting is the only rehabilitation method that permits replacement of the old pipe with a larger one.
In Pewaukee, the existing pipe consisted of three sections, all buried at about nine-feet deep. On the eastern-most end, where the pipe burst started, there was approximately 100 feet of C900 PVC pipe, eight inches in diameter. Moving westward, the next 200 feet consisted of 10-inch HDPE. The third and western-most section was 575 feet of eight-inch C900 PVC pipe.
The contractor, Advance Construction of Green Bay, WI, began construction by fusing together 40-foot sticks of HDPE pipe. It was specified as SDR 11 with a DIPS (Ductile Iron Pipe Size) equivalent of 12 inches. Advance sunk a 10-foot-deep insertion pit at the east end, and constructed two transition pits at the points where the pipe changed diameter and type. At the western transition pit, Advance placed a 40-foot trench box. The pipe bursting machine was anchored in the western-most pit.
Advance elected to pull the entire 875-foot run in one long pull, but with tooling changes at the transition points. For the job, the contractor chose to rent a HydroBurst HB 175 static pipe bursting machine from HammerHead Trenchless Equipment, Oconomowoc, WI. The machine features 175 tons of pull-back force and is powered by a 73-horsepower engine. The hydraulic system develops 4,000 psi of pressure and has a flow rating of 43 gallons per minute.
HDD created friction problem
For the 200-foot stretch of HDPE pipe, a specialized cutting head was developed to slice through the pipe. However, this pipe was installed by directional drilling in 2004, so it had only been in the ground for seven years. Furthermore, the HDPE pipe still had lubricant jell surrounding it. When the cutting head and expander began to pull through the 10-inch HDPE, there was not enough ground friction to hold the pipe in place to slit it.
“We knew that was going to be difficult,” says Ward. “That newer HDPE just expands, and we knew the chance of getting hung up on it was pretty high, because it won’t shatter. It just expands.”