Turnagain Slide Stabilization, Anchorage, Alaska

by Erwin Long,
Warren George,

Serial Information: Journal of the Soil Mechanics and Foundations Division, 1967, Vol. 93, Issue 4, Pg. 611-627

Document Type: Journal Paper


The Turnagain Slide was a large area of retrogresslve translatory sliding, resulting from the earthquake-induced liquefaction of soft sensitive Bootlegger clay including sand lenses. A slope-stability chart, derived from analysis of bluffs in the Anchorage area, indicated marginal earthquake stability of the area after sliding. Extremely low clay strengths under the toe of the slide along the seaward sloping surface indicated loss of this toe and the stabilization it provided in another earthquake. Stabilization model studies on blast remolding with sand drainage and later with electro-osmosis treatment were conducted. Tests conducted in early 1966 showed that soil strength under the seaward toe of the slide was of a magnitude such that the toe would not fail in an equivalent future earthquake. Recommendations were made to protect the slide toe against future erosion so that stability of the slide could be maintained. Investigation showed a pre-earthquake erosion rate of 2 ft to 10 ft per yr. Ice rafting of soil is believed to be a primary cause of erosion. Recommended erosion protection is a 1 on 3 rock-protected slope placed slightly seaward of the present high water elevation.

Subject Headings: Earthquakes | Soil strength | Soil liquefaction | Clays | Anchorages | Landslides | Soft soils | Slope stability | Alaska | United States

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