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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.

The freezing point of soils is the boundary of change of physical state from a thawed to frozen condition. A paramount factor which affects the transition zone is the quantity and composition of the dissolved salt in the pore water. The marine soils used in the experiments were from the arctic coast with a range in the granulometric composition. The clay fraction consisted of 40% kaolinite, 30% montmorillonite, 25% chlorite and 5% quartz. Salts used were from soil extractions or from sea water. NaCl and CaCl[ 2] solutions were also used for artificial salination of the soil samples. The salt content used ranged from 0.2 to 1% by weight or in terms of the pore water was from 0.006 to 0. 055. Three stages were observed; a supercooling stage, a phase of comparatively constant temperature, and a gradual fall of temperature. The supercooling temperature was from 1.5 to 2 times the freezing point. Conclusions are as follows: (a) the grain size characteristics of the soil do not influence the freezing point when the moisture content is in excess of the liquid limit; and (b) when there are equal concentrations of the interstitual solution only the qualitative composition of the salts influences the freezing point. Within the range investigated the freezing point of the soil is inversely proportional to the molecular weight of the soluble salts.

Adsorption of water has been studied extensively above 0 degrees C, but the problem of the phase transition of adsorbates in porous materials is presented at temperatures below 0 degrees C. Experiments that show how phase transitions modify length change-adsorption relationships are described. Adsorption-length change measurements from - 40 to -0.5 and isotherms at -20 and -0.5 degrees C were obtained. In another group of experiments different forms of isosteres were also obtained; the principle that water should be allowed to enter the sample at the low temperature was usually followed. Isotherms and length change- adsorption characteristics below 0 degrees C are qualitatively similar to those above 0 degrees C, but a decrease in adsorptive capacity and length change was observed. These results and those obtained from the isosteres lead to the conclusion that capillary condensation and menisci theories are operative and that a solid meniscus exists. It follows therefore that the saturated vapor pressure of frozen adsorbate is greater than that of bulk ice and that its volumetric expansion on freezing is similar to the bulk phase transition. It is shown how these phenomena can predict migration of water and generation of pressure within the porous body when it is subjected to cooling and warming cycles.