Alternative Approaches to Quantifying the Soil Freezing Characteristic Curve in Field and Laboratory Soils.

Abstract:

The soil freezing characteristic curve (SFC) quantifies the amount of unfrozen water co-existing with ice in frozen soils, as a function of temperature. The SFC influences the soil hydraulic properties and is especially crucial in understanding snowmelt infiltration and runoff, frost heave formation and thawing settlement in frozen soils. The SFC can be modelled by combining information from the soil moisture characteristic curve of unfrozen soils (SMC) with the Generalized Clapeyron Equation (GCE). While such an approach is straightforward and involves no additional free parameters, the resulting SFC is not always consistent with those observed in the field and laboratory. There is, therefore, a need to validate the GCE relationship against observed SFC, and it may be necessary to develop alternative relationships to facilitate accurate prediction of unfrozen moisture content in hydrological model.

This study sets out to obtain both field and laboratory data that quantifies the SMC and SFC for different soil textures and salinities and to compare the results with those obtained from the GCE and other alternative relationships. Data were collected from established seasonally frozen field sites in the prairies (St. Denis) and the boreal forest (BERMs Old Jack Pine site) in Saskatchewan, Canada. A column experiment was set-up in the laboratory to obtain SFCs for silica sand, with controlled pore-water salinity. Here we present results of the field and laboratory experiments. We developed three alternative models for the SFC, which differ in how they represent the effects of capillarity and salinity on the SFC, and we compare the models with observed values from the laboratory and field experiments.