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Playing Through: Pipe Bursting Upsizes Sewer Under Golf Course Without Interruption Of Play
With 175 tons of pulling force for pipes up to 24-inches, Moore thought at first the HB175 might be a little overkill for a 12-inch pipe upgrade project. It proved to be a fortunate choice under the fairway, however.
Hazards below the fairway
Titan Technologies’ Project Manager Clifton Cox described the challenges presented throughout the project. The existing pipe lay at 19-feet in a pipe-chip bed of crushed rock known by some as a “pit run,” which is sandy, cobbly dirt. Fracture sizes ran anywhere from ¾ inch to 12 inches, with eight-inch pieces being common. Such material does not displace nearly as easily as sand or clay. This makes pipe bursting more difficult even if just replacing same size pipe. However, this project required considerable expansion. To make room for 12-inch replacement pipe and the bell connections, the eight-inch pipe walls would be sliced and displaced by a 16-inch diameter bursting head. With such resistance from the pipe bed, displacement would be upward only.
Water was another complication. The Boise River was just yards away from the fairway in some places. For the fairway run it would also need to pass under a shallow slough. It was no surprise that the water table was found at only 2 ½ to three-feet deep during entry and extraction pit excavation.
The fairway pull required both pits to be 25-feet long by seven-feet wide and dug 18 to 20-feet deep. As Titan’s crews entered the water table at three feet, they pushed down four, 3-inch submersible pumps running off a 45 kW generator to dewater the hole. Three pumps were left to maintain the dewatered hole once the trench boxes were at depth. Over the three-day period, Thompson said, an estimated 680,000 gallons of water were moved from the pits.
The first run for this section of the project started in a manhole in the street’s right-of-way. The full 540-foot length of HDPE had been fused on the surface. Titan pulled it under the golf course fairway from that manhole to a manhole on the course. The pull posed no problem for the HB175, requiring about only 60 tons of force.
Beyond that second manhole, the last 80 feet of the run made a slight bend. It wouldn’t have posed much of a problem except that here the original pipe installers had switched to ductile iron. Mike Walk, the HammerHead technician who was on site during preparation and the pull itself, had seen projects like this before. Most likely the installers made the switch since they would be laying the sewer under surface water in this section.