• journal_title：Environmental & ; Engineering Geoscience
• Contributor：MARGARET M DARROW ; MATTHEW T BRAY ; SCOTT L HUANG
• Publisher：Association of Environmental & Engineering Geologists
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.2113/gseegeosci.18.3.261
• journal_abbrev：Environmental & Engineering Geoscience
• issn：1078-7275
• volume：18
• issue：3
• firstpage：261
• section：Articles

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.