ESTIMATING THERMAL-CONDUCTIVITY OF SOIL INSITU, WITH A NEW THERMAL PROBE

A simple system, using a thermal probe was designed to measure the thermal conductivity of a soil in situ. The operating conditions were investigated. The system was shown to be quite adapted for the field experiments. Measurements were made in a silty-clay-loam soil for different humidity and density conditions. As expected, the thermal conductivity increased with gravimetric water content and density of the soil. In the deeper layers, with homogeneous and larger densities, the thermal conductivity had high, steady values even at low water content, which may be due to the shrinkage of clay as the soil dries, compensating the diminution of thermal conductivity due to water losses. This behavior was quite different from that of the tilled surface layers with a granular structure. The measured values of thermal conductivity were higher than those found by laboratory methods using reconstituted soil samples. The absence of a reference method for in situ determination of the thermal conductivity did not allow us to completely validate this thermal probe.