Experimental system for simulating a natural soil temperature profile during freeze-thaw cycles

The methodologies used in the controlled manipulation of soil freeze-thaw cycles have varied widely. Despite their value in demonstrating the mechanisms of freeze-thaw action in soils, many methodologies do not replicate actual field conditions. Therefore, a simple soil thermal cycling system was developed to address several of the methodological weaknesses observed in previous laboratory experiments and to better assess the effects of freeze-thaw cycles on soil physical properties, water and pollutant transport, and microbial activity. The experimental system consisted of a 61- × 61- × 61-cm insulated bin containing four 15-cm diameter PVC lysimeters encased in sand, with a commercially-available heating cable located in the bottom of the sand mass. The heating cable created an upward heat flux representative of heat flow in soil under field conditions. The completed assemblage was placed on a cart, pushed into a walk-in freezer, and subjected to air temperatures from -10°C to 15°C. In order to test the system, the heating cable was set from 0°C to 5°C in 1°C increments to control the soil temperature at the 40-cm depth. Observed hourly air and soil temperatures, soil temperature gradients, and freezing and thawing rates were reported for three freeze-thaw cycles and compared to field values. The experimental system was able to produce a vertical temperature gradient in the soil of 0.08°C cm^-1 compared to a 0.07°C cm^-1 gradient observed under similar conditions in the field, and minimize large fluctuations in subsurface soil temperatures relative to changes in air temperature.