Monitoring and Analysis of Frozen Debris Lobes, Phase I

Abstract

A frozen debris lobe (FDL) is encroaching on the Dalton Highway near MP 219. FDLs appear
to consist of soil and rock, debris and potentially ice, although only preliminary surface
investigations have been conducted on these features thus far. Our knowledge of FDLs is
rudimentary, and we have more questions than answers about their internal stratigraphy and
mechanisms of movement. Preliminary studies indicate that the FDL at MP 219 is moving
toward the Dalton Highway at an average rate of 1 cm per day, and is currently less than 70 m
from the roadway. When it arrives at the highway, it will deliver about 22,000 tons of debris a
year. For a sense of scale, imagine a 50-ton truck dumping 440 truck-loads of debris onto the
highway annually. Should this mass of moving material further encroach upon the Dalton
Highway, it may impede the flow of essential goods and services to the oil and gas fields on the
North Slope, resulting in severe economic loss. Even before entering the highway right-of-way,
this FDL is affecting the highway by depositing a large volume of sediment against the highway
embankment, which has destroyed drainage by completely burying one culvert and partially
burying a second. The complete analysis of any landslide in a non-permafrost location requires
an understanding of its kinetics including knowledge of soil properties, direction and rate of
movement, and the nature of the shear zone; without this information, it is impossible to select
correct mitigation techniques. At the present time, such a comprehensive analysis is impossible
for FDLs, as we do not possess this information. To better understand movement of frozen
debris lobes, a drilling/sampling and monitoring program must be instigated.

The overall goal of this research is to determine the movement mechanism of FDLs. As Phase I
of this research, we will characterize the internal structure of a FDL through drilling and
sampling, and monitor its movement to determine the nature of the shear zone and rate and
timing of movement. We will compile a summary of the initial measurements and analysis for
delivery to the Alaska Department of Transportation and Public Facilities (ADOT&PF). These
initial results are necessary to guide future research efforts to aid in the development of an
appropriate mitigation plan. Contingent upon funding, Phase II of this research will consist of 1)
continued monitoring, 2) soil strength testing in the laboratory, 3) slope stability analysis, and 4)
working closely with ADOT&PF to develop mitigation strategies.

Final Report