Once soil temperature reaches a critical temperature due to heat generated from a heat source (e.g., ground-based heat exchangers, buried electrical cables), moisture migration is initiated, which may result in a significant change in soil thermal conductivity. In this study, laboratory testing was performed to evaluate how initial moisture content affects soil critical temperature. Temperature and moisture contents of three sandy soils at 1% and 3% initial moisture contents were measured using a radial-based apparatus, including a centrally placed heating element. While discontinuities near the boundary between dry and wet zones were clearly observed in soils at 3% initial moisture content, the 1% initial moisture content cases had gradual temperature profiles instead of pronounced discontinuities. Temperature and moisture profiles were thus used with soil images to determine critical temperature. As initial moisture content increased from 1% to 3%, moisture migration decreased with an increase in critical temperature average from 31.6 °C to 44.7 °C. This experimental data supports the concept that soil critical temperature is not a constant for a soil compacted to the same density and that other mechanistic attributes are causative.
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