Soil Sorptive Potential–Based Paradigm for Soil Freezing Curves

Abstract

The soil freezing curve (SFC) is a fundamental constitutive relationship between liquid water content and temperature under subzero (0°C or 273.15 K) conditions. SFC governs mechanical and hydrologic behavior of soil in freezing and thawing environments. The state-of-the-art SFC paradigms have been established empirically based on the capillary pressure-based Clapeyron equation. Two practical challenges prevent the rigorous use of the capillary pressure-based Clapeyron equation for realistic prediction of the SFC: (1) unable to use the governing pressure (intermolecular water pressure) for defining water phase change; and (2) unable to account for variations in latent heat of fusion and water density. A new paradigm based on soil sorptive potential (SSP) to predict the SFC from the soil water retention curve is developed, directly using the intermolecular water pressure distribution and pure water phase diagram in lieu of capillary pressure and the Clapeyron equation. The latest theory of SSP is used to quantify intermolecular water pressure distribution. Experimental validation demonstrates that the proposed paradigm yields excellent matches to the experimental SFC data for different soil types, and is a significant improvement over the predictions by the capillary pressure-based Clapeyron equation paradigm. The proposed paradigm reveals that the SFCs for various soils below 273.15 K (0°C) are mostly dominated by adsorptive water. Furthermore, the proposed paradigm can fully explain the practically encountered phenomenon that the SFC for soils with high clay content depends on the initial water content, whereas it does not for sandy soils. Practical significance of the new paradigm in geotechnical engineering problems is demonstrated through predicting soil moisture profiles under freezing and thawing, and permafrost environments.