Comparison of Two Laboratory Methods for Measuring the Critical Temperature of Sandy Soils

In this study, soil critical temperature was measured using two distinct approaches: (1) a temperature profile established from a heating element located at the top of a vertical column and (2) temperature and moisture profiles induced from a centrally placed heating source in a 'horizontal' apparatus. Steady-state thermal and moisture equilibrium took longer to establish in the horizontal apparatus (on average, nine hours longer); however, the resulting temperature and moisture profiles were more consistent in the horizontal apparatus and with easily discerned slope discontinuities between the dry and moist zones. More ambiguous temperature profiles were observed in the vertical apparatus, even with insulation and heat tape applied to minimize horizontal boundary losses. This is indicative of the difficulty in maintaining one-dimensional heat flow in a vertical column. As soil critical temperature is an important parameter used in designing underground infrastructure impacted by significant heat transfer, such as buried power cables, refinement and standardization of equipment and protocol for determining this parameter in a precise and mechanistically sound manner is of prime concern.