Positive Unintended Consequences: How Campbell Lake Gravity Sewer Pipeline Line Survived a Magnitude 7.1 Earthquake

Beta Construction of Seattle, Washington, began installation in November, 1989 of an 8,432 foot long 48-in. gravity sewer line that was installed across exclusive Campbell Lake in Anchorage, Alaska. In a unique and propitious series of events, the City of Anchorage and the Corps of Engineers collaborated on dam repairs and gravity sewer installation saving significant dollars for underwater construction and resulting almost 30 years later in unintended consequences. Unlike most unintended consequences, these were positive, even remarkably so. On November 30, 2018, a magnitude 7.1 earthquake struck the Alaska-Aleutian Subduction Zone and liquefied the lakebed. While the 29-year old 48-in. diameter gravity sewer installation was dramatically disturbed, and while the disturbance went unnoticed for 104 days under ice, there was no sewage spill and repairs were able to be made with minimal complications. This paper will highlight the circumstances of the original construction and how material selection and construction methods resulted in a positive outcome years later before the advent of today’s innovative and resilient seismic joints.