Recently, west coast pipe rehabilitation contractor ARB, Inc, Lake Forest, CA, was able to do something few contractors in North America have, replace a 6-inch 10 gauge steel water main with 8-inch HDPE through pipe bursting. The project, completed for the South Tahoe Public Utility District (STPUD), South Lake Tahoe, CA, was accomplished with the help of trenchless equipment manufacturer and Associate NUCA member TT Technologies, Aurora, IL. The existing 330-ft steel water main was being replaced as part of a water tank rehabilitation project. Because the line ran through a section of national forest, open cutting was not an option. Pipe bursting was the method of choice for this particular project. However, traditional pneumatic pipe bursting has been largely unsuccessful in bursting ductile and steel pipe. ARB Rehabilitation Manager Dave Arthurs turned to the hydraulically powered Grundoburst from TT Technologies.
The recently introduced Grundoburst 1000G (the largest of three models) is a hydraulically operated static bursting system. According to TT Technologies Pipe Bursting Specialist Collins Orton, several of the system’s features make bursting steel, as well as ductile iron, possible. He said, “During the static bursting process, a special bladed roller cutting head is pulled through the existing line by the bursting unit. As the bladed rollers are pulled through, they split the host pipe. An expander attached to the rollers forces the fragmented pipe into the surrounding soil while simultaneously pulling in the new pipe.” The specially designed bladed rollers are essential to the bursting process. The blades actually split the host pipe instead of ripping or tearing it. This makes the process very clean and prevents potential damage to the product pipe.According to Orton, this is a significant advancement in trenchless pipe replacement. He said, “I see this technology having a great impact on the gas and water industries. There are miles of steel and ductile iron lines in California and throughout North America that are undersized and/or deteriorating and need to be replaced. Some are even required by legislation to be replaced. Being able to replace and upsize these lines without digging them up, is a benefit to everyone.”
For the STPUD project the ARB crew dug a 5-ft x 15-ft launch at the beginning of the run and another 5-ft x 20-ft exit pit 330 feet away. The bursting unit was positioned in the exit pit and connected to a hydraulic power pack. The crew then began inserting the Quicklock bursting rods through the host pipe and into the launch pit. The patented rods are linked together, not threaded. This speeds installation and breakdown, and prevents twisting in the line during operation. A flexible guide rod attached to the front of the first rod was used to help ensure the smooth installation of Quicklock rods. Once at the launch pit, the ARB crew removed the guide rod and attached the bladed cutting wheels, bursting head, expander and new HDPE. The entire configuration was then pulled back through the host pipe by the hydraulic bursting unit. The 8-inch HDPE was installed without incident. After the HDPE was in place, the ARB crew removed the bursting equipment. The new main was then chlorinated, tested and put into service. Arthurs said, “Our crew was very impressed by how easy the machine was to operate. They were even more impressed that we were able to split steel pipe. Overall, we were very pleased with the results of the project. This was our first attempt bursting steel pipe. I anticipate a good deal more of this work in the future.”
by Jim Schill
Utility Contractor, March 2001, Pages 31,34