THERMAL CONDUCTIVITY OF DISTURBED SOILS UNDER LABORATORY CONDITIONS

The effect of salt concentration, organic matter, bulk density, and moisture content on the thermal conductivity of some sieved and repacked soils was investigated through laboratory studies. These laboratory experiments used the single probe method to determine thermal conductivity. The thermal conductivity observed in this study under varying water content, soil density, and soil texture was compared with independent estimates made using standard procedures of Campbell (1985). The differences between the observed and predicted results were very small. Fundamental information on how salts, water, and organic matter affect thermal conductivity of soil would be useful in modeling water and energy movement in systems containing salt-affected soils. The soils used were classified as sand, sandy loam, loam, and clay loam. 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 conductivity increased with increased soil density and moisture content. Thermal conductivity ranged from 0.43 to 0.98 for sand, from 0.35 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 1.30 to 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 decreased with an increase in the amount of added salts. Thermal conductivity for sand ranged from 1.17 to 0.56 W/m K at concentrations 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 to 0.05 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 for clay 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 at concentrations 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 to 0.05 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. The measurements concerning salts and organic matter are an important contribution to an important and little studied field.