Ninth International Conference on Permafrost ... - IARC Research

Freeze/Thaw Properties of Tundra Soils, with Applications to Trafficability on theNorth Slope, AlaskaIntroductionChristina F. BryantGeo-Watersheds Scientific, College Station, USARon F. PaetzoldGeo-Watersheds Scientific, College Station, USAMichael R. LillyGeo-Watersheds Scientific, Fairbanks, USAThis abstract focuses on the application of soil temperatureprofile data and its relationship to tundra-travel managementon the North Slope of Alaska, with particular attention towinter travel. Current standards regulate tundra-travel onthe North Slope of Alaska to conditions at or below -5°Cat a depth of 30 cm in the soil profile (Bader 2005). Theseregulations are meant to ensure adequate soil strength forsuch activities. Additionally, six inches of snow cover isneeded in the Coastal Plain region for tundra-travel to beopen.Frozen water affects tundra soils through added strengthfrom the addition of solids (ice) in soil pore spaces, whichdecreases slipping between soil particles. Soil cohesiveproperties are also augmented by frozen water, which“cements” soil particles to one another (Lilly et al. 2008).Thus, in areas where soil water content is high, soil strengthincreases during winter freezes, and conversely decreases inconjunction with summer thaws.Little or no data are available to assess travel limitationsresulting from seasonal freeze/thaw cycles of tundra soilson the North Slope, especially in areas of interest to thoseinvolved in the oil and gas exploration and field operations.Although this abstract makes no suggestions pertaining torevisions or alterations to current management standards, theknowledge gained in respect to freeze/thaw time constraintsand conditions on tundra-travel will aid others when makingsuch decisions. Data analysis is specifically useful whenassessing seasonal time limits on ice-road construction anduse as a basis of frozen soil freeze/thaw properties.MethodsA system of twelve weather stations was set up in northernAlaska in fall of 2006 and has since been collecting soilmoisture data by TDR, and soil temperature data fromThermisters each hour at 0, 5, 10, 15, 20, 40, 60, 80, 100,120, 135, and 150 cm depths (Fig. 1). These depths mayvary for some sites due to local soil conditions and thedepth of the active layer during sensor installations. Relativehumidity, dew point, wind speed and direction, wind chill,snow depth, solar radiation, net radiation, and snow and rainprecipitation data are also available from the data network.Station dataloggers are connected to radios, allowing fornear real-time measurement, which is specifically applicablewhen analyzing current conditions for tundra-travel.Figure 1. Map of meteorological station locations along the NorthSlope, Alaska.Soil temperature data were analyzed to show temporalvariation in one-degree incremental temperature conditionsin the freezing soils. Analyzing the differences in dates thatsoils reach these one-degree temperatures helps illustratethe potential differences in timing of tundra-travel openingswhen using different soil temperatures. Soil temperaturedata were also spatially examined to display the effects ofrelative location on timing of one-degree changes during theannual freeze/thaw cycle in the active layer.Results and DiscussionCurrent data analyses include plotted freeze/thaw cyclesfrom winter 2006 to summer 2007 for stations DMB2,37