Permafrost geotechnical index property variation and its effect on thermal conductivity calculations

Geotechnical borehole and sample data from three databases compiled by the Geological Survey of Canada were analyzed to determine the variability of geotechnical index properties within frozen soils. The analysis included 2662 boreholes with geological setting data, up to 60 m depth, within the Mackenzie Valley and Delta region of the Northwest Territories. A total of 7539 samples, each with soil and ice classifications and gravimetric moisture content data were included. Gravimetric and volumetric moisture contents were analyzed by general soil type to determine their coefficient of variation (COV) with depth and geologic setting. As expected, variability between geologic settings corresponded to the nature of the soil's depositional environment, and volumetric ice content variability decreased with increasing depth. General soil type was also used to determine the COV for dry density, specific gravity, and Atterberg limits for samples where testing was available. The variability of frozen thermal conductivities was estimated using Monte Carlo simulation and common equations from the literature based on the geotechnical index property variation. Recently-derived equations for thermal conductivity showed less variability compared to earlier methods.