The year was 1989. The place was Anchorage, Alaska. The project was the installation of a gravity sewer line beneath Campbell Lake while it was drained for dam repairs. While this type of project and installation is unique in itself, the pipeline’s performance during a magnitude 7.1 earthquake more than 30 years after it was installed is equally remarkable.
ADIP/ASWP Marketing Services Manager Maury D. Gaston presented virtually on this project in August at the American Society of Civil Engineers’ Utility Engineering & Surveying Institute (UESI) Pipelines 2020 Conference. Click here to read his conference paper in its entirety and here to watch a video recap of the project.
“This was a true demonstration of resilience and performance under extreme conditions,” Gaston said. “Although it experienced severe deflection during the earthquake, the pipeline remained intact and functional until repairs could be made months later.” In a separate presentation at UESI, Gaston defined resilience as the ability to continue performance after experiencing conditions beyond normal circumstances. “A 7.1-magnitude earthquake certainly qualifies,” he said.
The Campbell Lake Project was conducted by the Anchorage Water and Wastewater Utility (AWWU) in collaboration with the U.S. Army Corps of Engineers. The dam that forms Campbell Lake was damaged during a 100-year flood event in 1989. To repair the dam, the Corps of Engineers needed to drain the lake. At the same time, the AWWU was working on a project to construct a new sewer line to better serve the area, and this line needed to cross beneath Campbell Lake. The two groups coordinated to develop a cost-effective plan for installing the sewer pipeline. “As simple as it sounds, such coordination between agencies is not always the case,” Gaston said.
More than 8,000 feet of unrestrained 48-inch AMERICAN Fastite push-on-joint ductile iron pipe encased in polyethylene was installed for the project. Once in place beneath the lakebed, the pipeline was outfitted with concrete collars to hold it in place and prevent flotation, and the pipe was backfilled with aggregate to provide additional stability. The Campbell Lake sewer pipeline also included special deflection bells that were machined to allow greater-than-standard deflection.
The pipe was shipped 3,337 miles from Birmingham, Alabama, to Anchorage through a combination of rail, barge and truck, and freight costs were 28% of total delivered pipe costs. “AMERICAN’s Traffic and Shipping groups played a vital role in this, as they do in many projects,” Gaston said.
The gravity sewer line served the area well for years, and its strength and durability were put to the test on November 20, 2018, when a magnitude 7.1 earthquake occurred. The special deflection Fastite joint did not separate or leak even though the most severely deflected joint was calculated to have deflected 14 degrees, much greater than its rated special deflection of 4 degrees. In addition, the asphaltic topcoat and polyethylene encasement resulted in little to no corrosion, which allowed the pipeline to remain in pristine condition despite being buried for almost 30 years beneath the aggressive soil conditions of the lakebed.
“Even with the earthquake’s force and the disturbance to the pipeline, the 180-feet of pipe that was deflected and floated went unnoticed for 104 days, as it was held beneath a 16-inch-thick layer of ice,” Gaston said. “Once the ice began to melt, the dislocated ductile iron pipe became visible. No sewage spill occurred even with this severe deflection, and repairs were later made with minimal complications because of the robustness of the AMERICAN Fastite joint.
“While 1989 technology served exceptionally well for this project, today’s innovations would further ensure survivability and resilience,” Gaston said. “These include boltless and flexible restrained joints, including the workhorse Flex-Ring joint, the AMERICAN Earthquake Joint assemblies, metallized arc-sprayed zinc coating and V-Bio enhanced polyethylene encasement.
“In this installation in Alaska, as in so many in vastly different environments and circumstances across the country and around the world, ductile iron showed why it is the most dependable, robust and resilient pipe material, and proved its life-cycle value many times over,” Gaston said.