In situ apparent thermal conductivity measurement at depth in the unsaturated zone.

Abstract

Apparent thermal conductivity and diffusivity in the unsaturated zone were measured in situ using a heated resistance wire in backfilled, vertical holes and observation wells. Values of apparent thermal conductivity ranged from 0.00171 to 0.0061 cal/cm/sec/°C. The variation observed was due primarily to spatial moisture content differences in the medium. Overall, these values were consistent with results obtained by other researchers. Measurements were made where resistance wire and temperature sensor were I) in the same tube within one bore hole, II) in different tubes within one bore hole, and III) in different tubes within separate bore holes. Method III provided data with the least noise. Apparent thermal diffusivity values ranged from 0.00183 to 0.106 cm ²/sec. The higher values were obtained using methods I and II. The values obtained by method III agreed with results obtained by other researchers. However, the extra effort required for method III decreases its usefulness as a field method because thermal diffusivities can be measured easily and more accurately using other methods.