The city of Eureka, Calif., is nestled in Humboldt County on the state’s north coast, home to the redwood forest and a short drive from San Francisco. People travel from throughout the U.S. to enjoy and take in the area’s many attractions and outdoor activities.
Home to approximately 27,000 residents, Eureka played a large role in the California gold rush of the 1850s as an access point to Humboldt Bay. Despite its rich history, Eureka, like many U.S. cities and towns, now battles aging and deteriorating infrastructure that dates back, in some cases, more than 100 years.
The K Street Emergency Sanitary Sewer Main Rehabilitation project replaced approximately 600 ln ft of 107-year-old, 14-in.-diameter vitrified clay sanitary sewer main. This main conveys approximately 70% of the wastewater flow from a 100-acre collection basin and is located two blocks from Humboldt Bay. It was suffering from extreme root intrusion.
According to Deputy Public Works Director Bruce Young: “This sewer main is a major trunk line within the collection system, and any associated blockage and overflow would have resulted in a large sewer spill in close proximity to Humboldt Bay, potentially causing environmental damage and disruption of shellfish harvesting. [It] would have exposed the city to fines and possible lawsuits as a result of the spill.”
Wahlund Construction, Inc., Eureka, was contracted to pipeburst and replace the existing main with 16-in.-outer-diameter, high-density polyethylene (HDPE) pipe. For the project, a 14-in.-diameter Grundocrack Koloss with a 19-in. rear expander pipe bursting system from TT Technologies, Inc., Aurora, Ill., was used in conjunction with a 20-ton constant-tension Grundowinch.
“The section of main to be replaced is located between 4th and 2nd streets, with 110 ft at the downstream end running under a pedestrian plaza,” said Angi Sorensen, city project engineer.
During pneumatic pipebursting, the pipebursting tool is guided through a fracturable host pipe by a constant tension winch. As the tool travels through the pipe, its percussive action effectively breaks apart the old pipe and displaces the fragments into the surrounding soil. Depending on the specific situation, the tool is equipped with an expander that displaces the host pipe fragments and makes room for the new pipe. As the tool makes its way through the host pipe, it simultaneously pulls in the new pipe—usually HDPE.
With expanders, one tool can be used to burst several differently sized host pipes and replace them with new HDPE of the same size or larger. Pipebursting is the only trenchless method of rehabilitation and replacement that allows for upsizing of existing pipe.
Within two weeks of meeting with the city to discuss the project, Wahlund Construction assembled a team. Munson Pump Services (MPS), Cottonwood, Calif., was responsible for constructing and operating a bypass to convey the wastewater flow around the project area. The bypass system included redundant pumps at the receiving pit, one pump at each of the two alleys within the project area and traffic-rated ramps at 3rd Street. It operated continuously for more than three weeks, with 24-hour MPS monitoring.
After the bypass was established, workers began preparing to burst the 600-ft section of sewer main. Launch and exit pits were dug on either side of the length of main; the launch pit was located at the north end of the run and the exit pit at the south. The exit pit measured approximately 8 ft wide by 40 ft long by 14 ft deep, and a section of an 8-in. water main had to be removed to accommodate the trench box. A 10-ft section of the water main was exposed at each of the two alleys where the alley mains were bypassed, and the manholes were removed and replaced.
According to Sorensen, the initial plan was to break the project into separate runs, but TT Technologies’ technical support staff determined that the burst could be accomplished in a single run. The bursting head traveled at an average velocity of 6 ft per minute for most of the run, slowing to about 1.5 ft per minute for the last 100 ft or so.
The entire project took approximately one month to complete, including mobilization; bypass installation; excavations at launch and receiving pits; removal of three manholes; pipe bursting; connections between existing and new pipes; bypass removal; water line replacement; manhole reconstruction; backfill; surface restoration; and demobilization.