Abstract

A man-made island and buried subsea pipeline are needed for an oil production project within the Foggy Island Bay area of the Alaskan Beaufort Sea. In order to characterize the geologic and permafrost conditions in the area, field data have been collected over several winter field seasons. Multiple subsea buried pipeline alignment options and several potential island sites have been studied. Over the years, the arctic exploration teams have completed 600 boreholes, 75 piezocone penetration test (CPT) soundings, subsea temperature measurements, and performed comprehensive laboratory programs on frozen and unfrozen sediments. The shallow subsurface geologic conditions within Foggy Island Bay range from loose silty sand and soft to firm fine-grained marine Holocene deposits to stiff Pleistocene silty clay deposits. Shallow permafrost is present in Foggy Island Bay, primarily near the Boulder Patch and within the shoreline transition zone. The results of the near surface geotechnical conditions are discussed and presented with respect to subsea pipeline constructability and design parameters. Trench constructability and wall stability is discussed, as well as the frozen and unfrozen backfill properties important to resist upheaval buckling when the pipeline goes into production and begins to thaw the frozen backfill. This geotechnical summary serves as a resource for enhanced understanding of soil, permafrost, and sea-ice properties in the Alaskan Beaufort Sea.

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