Documenting the Collision of a Landslide in Permafrost with a Highway Embankment

Abstract

Frozen debris lobes (FDLs) are slow-moving landslides in permafrost. FDL-A, the largest monitored FDL in the Brooks Range of Alaska, has steadily progressed downslope toward the Dalton Highway, which is the only road to the oil and gas fields of the North Slope. To avoid this encroaching landslide, the Dalton Highway was realigned farther downslope in 2018. The abandoned portion of the highway was left in place, providing a unique opportunity for a full-scale field experiment to monitor the impact of a landslide on an engineered structure. In 2020, we conducted a subsurface investigation, drilling and sampling the subsurface soils and installing geotechnical instrumentation within the abandoned highway embankment. Here, we present the integration of multiple datasets to provide a detailed description of the landslide–embankment collision. FDL-A is shearing within weathered bedrock»7.6 m below the embankment surface. It horizontally displaced a portion of the embankment»0.3 m as of November 1, 2023. Using the infinite slope approach and strength properties determined from laboratory testing, we estimate that FDL-A is impacting the highway embankment and underlying soils with at least 77.8 kN/m width shear force. As this force occurs approximately 4 m below the bottom of the embankment, we postulate that the presence of the abandoned Dalton Highway embankment does little to stop FDL-A’s downslope progression.