The measurement of soil parameters, such as the permeability and shear strength functions, used to describe unsaturate soil behaviour can be expensive, difficult, and often impractical to obtain. This paper proposes a model for predicting the shear strength (versus matric suction) function of unsaturated soils. The prediction model uses the soil-water characteristic curve and the shear strength parameters of the saturated soil (i.e., effective cohesion and effective angle of internal friction). Once a reasonable estimate of the soil-water characteristic curve is obtained, satisfactory predictions of the shear strength function can be made for the unsaturated soil. Closed-form solutions for the shear strength function of unsaturated soils are obtained for cases where a simple soil-water characteristic equation is used in the prediction model. Key words: soil suction, soil-water characteristic curve, shear strength function, unsaturated soil.

A review of hysteresis models for soil-water characteristic curves is presented. The models can be categorized into two groups: (i) domain models (or physically based models) and (ii) empirical models. Some models are capable of predicting scanning curves, while other models are capable of predicting the boundary wetting curve and the boundary drying curve. A comparison of the ability of five selected models to predict the boundary wetting curve showed that the Feng and Fredlund model with enhancements by Pham, Fredlund, and Barbour appears to be the most appropriate model for engineering practice. Another comparison among five physically based models for predicting scanning curves showed that the Mualem model-II gives the best overall prediction of scanning curves. The study showed that taking the effect of pore blockage into account does not always give a better prediction of hysteretic soil-water characteristic curves. A scaling method for estimating the initial drying curve, the boundary wetting curve, and the boundary drying curve is also presented in the paper.Key words: soil-water characteristic curve, hysteresis model, comparison, boundary curve, scanning curve, unsaturated soils.

Traditional methods of evaluating evaporation provide an estimate of the maximum or potential rate of evaporation determined on the basis of climatic conditions. Methods such as these are appropriate for open water or fully saturated soil surfaces. Actual rates of evaporation from unsaturated soil surfaces are generally greatly reduced relative to the potential rate of evaporation. A theoretical model for predicting the rate of evaporation from soil surfaces is presented in this paper. The model is based on a system of equations for coupled heat and mass transfer in soil. Darcy's Law and Fick's Law are used to describe the flow of liquid water and water vapour, respectively. Heat flow is evaluated on the basis of conductive and latent heat fluxes. Dalton's Law is used to calculate the rate of soil evaporation to the atmosphere based on the suction at the soil surface. The soil–atmosphere model was used to predict soil evaporation rates, water-content profiles, and temperature profiles for a controlled column evaporation test over a 42 day period. The values computed by the soil–atmosphere model agreed well with the values measured for two columns of Beaver Creek sand in the evaporation test. Key words : modelling, evaporation, unsaturated, soil surfaces.

The mechanical behavior of compressible clay soils may be strongly influenced by physicochemical effects when concentrated pore fluids are introduced to the soil. Conceptual models have been used to explain the influence of pore fluid chemistry on the mechanical behavior of clays in a qualitative way. In this paper an alternate macroscopic description of the osmotic volume change behavior of a clay soil undergoing changes in pore fluid chemistry is provided.Theoretical descriptions of two potential mechanisms of osmotic volume change (osmotic consolidation and osmotically induced consolidation) are presented. Osmotic consolidation occurs as a result of a change in the electrostatic repulsive-minus-attractive stresses, R — A, between clay particles. Osmotically induced consolidation occurs because of fluid flow out of the clay in response to osmotic gradients.A numerical simulation is used to demonstrate the characteristic behavior of a clay soil undergoing either of these volume change processes. The results of a laboratory testing program on two clay soils exposed to concentrated NaCl solutions are used to illustrate that the dominant mechanism of osmotic volume change in surficial clay soils is osmotic consolidation. Key words: physicochemical, osmosis, volume change, NaCl salt, montmorillonite, clay, stress state variables, R – A.

This paper presents a theoretical approach in which a Dalton-type mass transfer equation is used to predict the evaporative fluxes from nonvegetated soil surfaces. Soil evaporation tests were conducted in the laboratory on three different soil samples of Beaver Creek sand, Custom silt, and Regina clay. The soil surfaces were saturated and allowed to evaporate to a completely air-dried state. The actual evaporation rate for each soil surface was measured along with the potential evaporation rate for an adjacent water surface. The ratio of actual evaporation to potential evaporation or normalized soil evaporation was then evaluated with respect to drying time, soil-water content, and soil suction. The value of the normalized soil evaporation was found to be approximately equal to unity for all soils until the total suction in the soil surfaces reached approximately 3000 kPa. The rate of actual soil evaporation was observed to decline when the total suction exceeded 3000 kPa. A relationship between the actual evaporation rate and total suction was found to exist for all three soil types which appears to be unique and independent of soil texture, drying time, and water content.Résumé : Cet article présente une approche théorique dans laquelle une équation de transfert de masse de type Dalton a été utilisée pour prédire les flux d'évaporation des surfaces de sol non couvertes de végétation. Des essais d'évaporation des sols ont été faits en laboratoire sur trois échantillons de sols différents, soit un sable de Beaver Creek, un silt Custom, et une argile de Regina. Les surfaces du sol ont été saturées et soumises à une évaporation jusqu'à un état de sècheresse complète à l'air. La vitesse réelle d'évaporation pour chaque surface de sol a été mesurée en même temps que la vitesse d'évaporation potentielle d'une surface d'eau adjacente. Le rapport de l'évaporation réelle sur l'évaporation potentielle, ou l'évaporation normalisée du sol, était alors évalué par rapport au temps de séchage, de la teneur en eau et de la succion du sol. L'on a trouvé que la valeur de l'évaporation normalisée du sol était approximativement égale à l'unité pour tous les sols jusqu'a ce que la succion totale dans les surfaces de sol atteignent approximativement 3000 kPa. L'on a observé que la vitesse de l'évaporation réelle du sol diminue lorsque la succion totale dépasse 3000 kPa. Il existe une relation entre la vitesse d'évaporation réelle et la succion totale pour les trois types de sol qui semble être unique et indépendante de la texture du sol, du temps de séchage, et de la teneur en eau.