Water Content In Frozen Soils Research Articles

Modeling the Unfrozen Water Content of Frozen Soil Based on the Absorption Effects of Clay Surfaces

AbstractUnfrozen water content significantly affects the thermal‐hydro‐mechanical characteristics of frozen soil. Currently, theoretical explanations for the presence of unfrozen water include capillary action, surface effects, adsorption forces, and the electrical double layer. However, the relationships between unfrozen water and these actions are not well explained, except for capillary forces. In addition, although frost heave experiments indicate that the electrical double‐layer solution on a clay particle contains the main portion of unfrozen water, the electrical double‐layer theory which produces a cation solution has not previously been used to calculate unfrozen water content. In this paper, it is assumed that the residual unfrozen water at very low temperatures (below −18°C) is held within the adsorption‐layer solution and that the remaining unfrozen water within the influence of surface effects is the cationic solution in the diffuse layer. Based on these assumptions, a theoretical model of unfrozen water is established with independent variables of temperature, specific surface area, and electrical double‐layer parameters. While the input parameters of the theoretical model are numerous and difficult to obtain, the theoretical model is simplified as a parametric model. Results of the parametric model are strongly consistent with experimental data within a certain temperature range, supporting the hypothetical conditions. The similarity in the underlying mathematical structure of the derived theoretical and parametric models to current semi‐empirical models further suggests that the surface effects of clay are the main causes of unfrozen water in frozen soil.

Characteristics of Unfrozen Water Content in Frozen Soils and Its Effect on Flexural Strength

Unfrozen water content (UWC), which affects the mechanical behavior of frozen soil, was investigated over a continuous temperature range using an isothermal adiabatic calorimeter. The employed soil materials were fine sand, clay and a mixture of fine sand and clay. Water, with or without NaCl, was added to the soil materials. Specimens were obtained by freezing the saturated soils rapidly. The UWC increased with salt concentration and content of fine soil particles. A temperature rise increased the UWC in all frozen soils. A rapid increase in UWC was observed around the eutectic point of saline frozen sand. However, the rapid increase was not observed for saline frozen clay. Total UWC was divided into UWC in brine and absorbed UWC. It was found that the UWC in brine decreases with the content of fine soil particles. Then, the flexural strength of frozen soils was examined for various characteristics of UWC. The dependence of flexural strength on salt concentration was agreement with the dependence on UWC in brine, and the dependence of flexural strength on the content of fine soil particles was in agreement with the dependence on absorbed UWC. The flexural strength of frozen soils, including those containing both salt and fine soil particles, was not determined by the total UWC, but predominantly by UWC in brine.

Unfrozen Water Content of Frozen Soils and Soil Moisture Suction

Synopsis The unfrozen water content of various soils has been measured by calorimeter. The suction-moisture content characteristics of the same soils were also determined at room temperature, with conventional pressure plate and pressure membrane apparatus. Using the values of unfrozen water content measured during freezing, and the suction characteristics obtained during drying, a relation was found between the two sets of results. The relationship approximates that of Schofield, between suction and initial freezing point, of soils at various moisture contents. Knowledge of the relationship permits prediction of the amount of water remaining unfrozen in a soil at negative temperatures down to −1·0°C and often some what lower. Such prediction requires only determination of suction-moisture content characteristics by conventional methods together with a simple determination of the freezing point of an extract of the soil solution. In many cases, the accuracy of the prediction is apparently as great as can be obtained using even complex calorimetric methods. Using these relatively easily determined values of unfrozen water content at various temperatures, realistic estimates can be made of the apparent specific heats of frozen soils. The observed relationship provides a basis for studies of the effects of both load and temperature, on the proportions of ice and water in frozen soils and on the state of stress within the ice and unfrozen water. La teneur en eau non gelée de divers sols, a été mesurée par calorimètre. Les caractéristiques des teneurs eau-succion des mêmes sols furent aussi déterminées à la température ambiante, avec plaque conventionnelle de pression et appareil à membrane de pression. En utilisant les valeurs des teneurs en eau non gelée mesurées pendant la congélation, et les caractéristiques de succion obtenues pendant le séchage, un rapport fut trouvé entre les deux séries de résultats. Le rapport se rapproche de celui de Schofield, entre la succion et le point initial de congélation de sols de diverses teneurs en eau. La connaissance du rapport permet de prédire la quantité d'eau restant non gelée dans le sol à une température descendant jusqu'à −1·0°C et souvent quelque peu plus basse. Une telle prédiction nécessite seulement la détermination des caractéristiques de la teneur eau-succion par les méthodes conventionnelles, ainsi qu'une détermination simple du point de congélation d'un prélèvement de solution du sol. Dans beaucoup de cas, l'exactitude de la prédiction est apparemment aussi grande que celle qui peut être obtenue même en utilisant des méthodes calorimétriques complexes. En utilisant ces valeurs déterminées d'une manière relativement facile de teneur en eau non gelée à diverses températures, on peut faire des évaluations réalistiques des chaleurs spécifiques apparentes des évaluations réalistiques des chaleurs spécifiques apparentes des sols gelés. Les rapports observés fournissent une base pour les études des effets à la fois de charge et de température, sur les proportions de glace et d'eau dans les sols gelés et sur l'etat des contraintes dans la glace et l'eau non gelée.