Alyeska pipeline milepost 687 is in the Copper River Basin of Alaska approximately 3 miles south of Glennallen. The project site is on the north facing slope of the Tazlina River valley; the slope is steep at approximately 30%. Soils in the project area primarily consist of perennially frozen glaciolacustrine deposits of clay and silt underlain by sequenced deposits of silt, sand, and gravel. The pipeline is supported above ground on passively-cooled thermal vertical support members. Active, bimodal, retrogressive landslides/flows are common along the south slope of the valley.
Long term temperature and ground movement monitoring shows relatively slow downhill ground movement is occurring near the top of permafrost and within active layer soils across the slope. Slow downhill movement is causing VSM’s to translate and tilt, requiring continued shoe adjustments, load redistribution, and split ring adjustments. The goal of this project was to mitigate slope movement, stop progressive tilting and translating VSM’s, reduce long term maintenance efforts, and reduce long-term degradation of permafrost.