Monitoring and Analysis of Frozen Debris Lobes, Phase I
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2012-12-01
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Edition:Final report.
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NTL Classification:NTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENT;NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATION;NTL-SAFETY AND SECURITY-Highway Safety;
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Abstract:A slow-moving landslide (termed Frozen Debris Lobe-A (FDL-A)) is approaching the Dalton Highway near MP 219, at a distance of 195 ft from the northbound shoulder as of November 2012. Previous analysis of images from 1955 through 2008 indicated an average movement rate of 0.4 in. per day. To better understand the movement of FDL-A, including its soil properties, the direction and rate of movement, and the nature of the shear zone, we initiated a drilling/sampling and monitoring program in 2012. Based on the drilling results, FDL-A consists of silty sand with gravel, overlying white mica schist bedrock at a depth of 86.5 ft (where drilled). Measurements indicate that temperatures within FDL-A average 30ºF, which is 2ºF warmer than the surrounding permafrost. Water pressure exists within this feature, demonstrating a potentiometric surface 35 ft above the lobe surface. FDL-A demonstrated at least two modes of movement, with a shear zone between 66 ft and 74 ft below ground surface, and slow to moderate flow above this depth; combining these, FDL-A was moving at an average rate of 1.0 in. per day between September and November 2012. Recommendations for future work are included in our report.
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