ABSTRACT

Frozen debris lobes (FDLs) are large masses of soil, rock, incorporated organic material, and ice moving down permafrost-affected slopes. In this paper, we focus on FDL-A in the south-central Brooks Range, Alaska, which is an impending geohazard to the Dalton Highway, located just under 40 m away from the highway embankment. We present the results of multi-faceted research, including field-based studies, laboratory testing of soil samples, slope stability analysis, and a geographic information system (GIS) analysis. Subsurface instrumentation indicates that major movement of FDL-A occurs in a shear zone 20.6 to 22.8 m below the ground surface, with temperature-dependent internal flow as a secondary movement mechanism. Surface measurements show an overall average rate of movement of 1.2 cm per day, which is an increase over historic rates. The slope stability analysis required a back analysis to determine soil strength parameters at failure, resulting in cohesion values between 43 and 53 kPa and friction angles between 10° and 16°. The modeling results indicated a high sensitivity to pore-water pressure and cohesion. This is critical since the melting of massive ice and thawing of frozen soil will increase pore-water pressure and lower shear strength, resulting in the acceleration of FDL-A towards the Dalton Highway. The GIS analysis also provided insight into the movement and instability of FDL-A and provided groundwork for a GIS protocol for examining catchment and lobe features of all FDLs along the highway corridor.

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