This paper intends to develop a generalized thermal conductivity model for moist soils that is based on the concept of normalized thermal conductivity with respect to dry and saturated states. This model integrates well the effects of porosity, degree of saturation, mineral content, grain-size distribution, and particle shape on the thermal conductivity of unfrozen and frozen soils. The thermal conductivity for saturated soils is computed with the use of a well-known geometric model that includes the unfrozen water content in frozen fine-grained soils. Nearly 220 experimental results available from the literature were analysed to develop a generalized empirical relationship to assess the thermal conductivity of dry soils. A general relationship between the normalized thermal conductivity of soils and the degree of saturation using a soil-type dependent factor was used to correlate the normalized thermal conductivity for more than 650 test results for unfrozen and frozen moist soils, such as gravels, sands, silts, clays, peat, and crushed rocks.Key words: heat transfer, soils, degree of saturation, mineral content, unfrozenfrozen, thermal conductivity.
[1] Most classical predictive models of unsaturated hydraulic conductivity conceptualize the pore space as either bundles of cylindrical tubes of uniform size or assemblies of cylindrical capillary tubes of various sizes. As such, these models have assumed that liquid configuration is the same in both the wet and dry ranges and that a single concept can be used to describe water transport over the entire range of matric head. Yet theoretical and experimental findings suggest that water transport in wet media, which mostly occurs in water saturated capillaries, is quite different from that in dry media, which occurs in thin liquid films. Following these observations, this paper proposes a new model for predicting the hydraulic conductivity of porous media that accounts for both capillary and thin film flow processes. As with other predictive models, a mathematical relationship is established between hydraulic conductivity and the water retention function. The model is mathematically simple and can easily be integrated into existing numerical models of water transport in unsaturated soils. In sample calculations, the model provided very good agreement with hydraulic conductivity data over the entire range of matric head. Two other well-supported models, on the other hand, were unable to conform to the experimental data.
This study reveals that a freezing soil can be characterized by two parameters, the segregation-freezing temperature Ts and the overall permeability of the frozen fringe [Formula: see text]. During unsteady heat flow, the variation of these parameters with temperature produces rhythmic ice banding in fine-grained soils. At the onset of steady-state conditions, freezing tests conducted at a fixed warm end temperature showed that Ts was independent of the cold side step temperature. In addition, a model is presented that indicates how the overall permeability of the frozen fringe can be calculated without detailed measurements at the scale of the frozen fringe. It is also constant in the tests reported here.
In previous work it has been shown that when a soil sample freezes in a one-dimensional manner under different cold-side step temperatures but the same warm-side temperature, at the formation of the final ice lens the water intake flux is proportional to the temperature gradient across the frozen fringe. The constant of proportionality has been called the segregation potential and this linear relation constitutes the coupling between heat and mass flow in a general theory of frost heave. This paper shows experimentally that the segregation potential is also a function of the average suction in the frozen fringe which is readily expressed in terms of the suction at the frost front. As a result it is also shown that measured water intake flux during freezing is dependent on the freezing path used to initiate the final ice lens. A thermodynamic explanation of the dependence of segregation potential on suction in the frozen fringe is also offered.Dans une etude antCrieure diffgrents Cchantillons d'un m&me sol ont Ct C gelis unidirectionnellement avec differentes temperatures nCgatives B l'une des extrCmitCs mais en conservant toujours la m&me tempCrature h la base non gelCe. Dans ces conditions, il a Ct C dCmontrC que le flux de l'eau aspirCe par les Cchantillons Ctait proportionnel au gradient de tempCrature h travers la frange gelCe lors de la formation de la dernikre lentille de glace. Ce facteur de proportionnalitk reprtsente le potentiel de sCgrCgation du sol. Cette relation linCaire est le lien entre les transferts de masse et de chaleur de la thCorie gouvernant le soukvement lors du gel. Le prCsent article demontre que le potentiel de sCgrCgation est Cgalement dependant de la succion moyenne dans la frange gelke qui est directement relite h la succion existante h l'interface entre le sol gel6 et non gelC. I1 est Cgalement dCmontrC que le flux de l'eau mesure lorsque la dernikre lentille de glace se forme depend du cheminement utilisC pour initier cette lentille. Une analyse thermodynamique est prCsent6e permettant d'expliquer la dependance du potentiel de sCgrCgation par rapport B la succion moyenne dans la frange gelCe.
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