THERMAL CONDUCTIVITY OF DISTURBED SOILS UNDER LABORATORY CONDITIONS

Abstract

The effect of salt concentration, organic matter, bulk density, and moisture content on the thermal conductivityof some sieved and repacked soils was investigated through laboratory studies. These laboratory experiments used thesingle probe method to determine thermal conductivity. The thermal conductivity observed in this study under varyingwater content, soil density, and soil texture was compared with independent estimates made using standard procedures ofCampbell (1985). The differences between the observed and predicted results were very small. Fundamental informationon how salts, water, and organic matter affect thermal conductivity of soil would be useful in modeling water and energymovement in systems containing salt-affected soils. The soils used were classified as sand, sandy loam, loam, and clayloam. The three salts used were sodium chloride (NaCl), magnesium chloride (MgCl 2 ), and calcium chloride (CaCl 2 )while addition of peat moss was to increase the organic matter content. For the type of soils studied, thermal conductivityincreased with increased soil density and moisture content. Thermal conductivity ranged from 0.43 to 0.98 for sand, from0.35 to 0.55 for sandy loam, from 0.34 to 0.50 for loam, and from 0.29 to 0.44 W/m K for clay loam at densities from 1.30to 1.50 g/cm 3 and water contents from 0.06 to 0.10 cm 3 /cm 3 . The results also showed that thermal conductivity decreasedwith an increase in the amount of added salts. Thermal conductivity for sand ranged from 1.17 to 0.56 W/m K atconcentrations of NaCl from 0.02 to 0.10 kg/kg, from 1.13 to 0.52 W/m K at concentrations of CaCl 2 from 0.01 to0.05 kg/kg, and from 1.05 to 0.45 W/m K at concentrations of MgCl 2 from 0.01 to 0.05 kg/kg. Thermal conductivity forclay loam ranged from 0.61 to 0.16 W/m K at concentrations of NaCl from 0.02 to 0.10 kg/kg, from 0.58 to 0.10 W/m K atconcentrations of CaCl 2 from 0.01 to 0.05 kg/kg, and from 0.55 to 0.08 W/m K at concentrations of MgCl 2 from 0.01 to0.05 kg/kg. At a given moisture content, increasing the percentage of soil organic matter decreased thermal conductivity.Finally, thermal conductivity values were higher for sand than for clay loam for the same salt type and concentration. Themeasurements concerning salts and organic matter are an important contribution to an important and little studied field.