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Title:	Heat transfer and frost-thaw penetration in soil surrounding an inclusion of sand: Numerical model results relevant to electromagnetic sensor system performance
Authors:	United States. Air Force. Electronic Security and Communications Center for Excellence. Peck, Lindamae. O'Neill, Kevin, 1946-
Keywords:	Buried electromagnetic sensor Heat transfer Heat trasmission Sand inclusion Freeze–thaw Moisture content Soil temperature Frost depth Numerical simulations Winter weather Frozen ground
Publisher:	Cold Regions Research and Engineering Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Series/Report no.:	CRREL report ; 95-13.
Description:	CRREL Report Abstract: One- and two-dimensional numerical simulations of heat flow in silty soil with and without a sand inclusion (15 cm thick, variable width) have determined the magnitude and the lateral extent of the disruption in frost and thaw penetration attributable to the presence of the inclusion. Four different soil temperature histories, derived from field data at a Vermont site, were used as the surface boundary condition for the winter-long simulations. This identified differences in frost depth and soil temperature resulting solely from an overall colder or warmer soil surface condition. For a given surface boundary condition, the moisture content of the soil was varied (10, 17 or 25%, by weight) to contrast the changes in frost penetration caused by the moisture-dependent differences in soil thermal conductivity and latent heat. The drier sand (3% moisture content by weight) with its smaller latent heat freezes more rapidly than does the soil under identical conditions, so initially (early winter) frost penetration is greater (by 5–6 cm) when the sand inclusion is present because the freezing front proceeds rapidly through the sand. Subsequently, the freezing front is deeper (by a maximum of 11 cm) in soil without a sand inclusion. The less conductive sand impedes heat flow toward the soil surface, resulting in higher soil temperatures beneath the inclusion, which in turn retards freezing of the soil. Frost penetration beneath a sand inclusion is deeper the drier the soil is; with no sand inclusion present, frost depth is greater the more moist the silty soil is. Under the conditions of this study, maximum frost penetration is 61 cm (“coldest” surface boundary condition, 25% moisture content soil, no sand inclusion). The change in maximum frost depth because of the presence of a wide sand inclusion is large relative to overall frost penetration. Similarly, the difference in soil temperature at a given depth, although small, can correspond to a large difference in unfrozen moisture content of the silty soil. Under either relatively mild or “normal New England” winter conditions, the presence of a sand inclusion is probably beneficial to the performance of a buried electromagnetic sensor system, which is more reliable in dry or frozen soil because of the soil’s lower electrical conductivity. A sand inclusion may not lead to improved sensor performance under more severe winter conditions, which cause much lower soil temperatures and much deeper frost penetration.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/9193
Appears in Collections:	CRREL Report