Calculating maximum frost depths at Mn/ROAD : winters 1993-94, 1994-95 and 1995-96
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1997-03-01
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Edition:Final report--1996
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Abstract:This effort involved calculating maximum frost penetration depths for each of the 40 test cells at Mn/ROAD, the Minnesota Department of Transportation's pavement testing facility, for the 1993-94, 1994-95, and 1995-96 winters. The report compares results with measured maximum frost penetration depths for the same three winters. Generally, calculated depths were within plus or minus 15% of measured depths, but differences were much greater for the four test cells underlain by the granular subgrade. Researchers conducted sensitivity tests to determine the influence of the n-factor, soil moisture content, material density, layer thickness, thermal conductivity, mean annual soil temperature, and volumetric latent heat of fusion. Conclusions included the following: (1) Small variation in layer thickness will have a very minor effect on computed frost depths; (2) Reasonable variations in moisture content and density of the various base course, subbase course, and subgrade layers will have a minor effect on calculated frost penetration depths; (3) Large n-factors caused deeper calculated frost penetration depths, and the use of n-factors of .90 and .95, respectively, for flexible and rigid pavements provided the most reasonable estimates of frost depths; (4) Increasing the thermal conductivity of the materials by 25% resulted in closer calculated agreement with measured frost depths; and (5) Using a mean annual soil temperature of 9.4 deg C rather than 11.1 deg C resulted in better agreement between calculated and measured data. Tables, figures. 1879k, 70p.
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