Abstract

A portion of the Richardson Highway near Glennallen, Alaska, is threatened by slope movement in an area where the highway travels along a bluff overlooking the Copper River. Analysis of aerial photographs indicates that portions of the bluff have experienced an average of 1.5 m of retreat per year since 1979, and gully erosion has completely obliterated portions of the pre-1965 highway alignment. The subsurface consists of a 1.5-m-thick surficial silt layer underlain by frozen, ice-rich clayey soils with an average annual temperature of −0.56°C. At 16 m below the ground surface, the soils become ice-poor and coarser grained. In situ measurements, soil creep tests, and slope stability analysis indicate that the ice-rich clayey soils are experiencing movement, with creep velocities of up to 2.5 cm per year. This deep-seated creep results in fracturing of the near-surface soil layer that is manifested at the surface by cracks, scarps, and back-tilted blocks. Groundwater perched above the permafrost table and seeping toward the bluff face facilitates the rapid retreat of the bluff edge through the formation of gullies.

You do not currently have access to this article.