The coefficient of permeability function is an important unsaturated soil property required when modeling seepage and contaminant transport phenomena. Inaccuracies in the estimation of the permeability function can lead to significant errors in numerical modeling results. Changes in void ratio and degree of saturation are factors that influence the permeability function. Presently available methodologies for estimating the unsaturated permeability function make the assumption that there is no volume change as soil suction is changed. As a result, volume changes are interpreted as changes in degree of saturation. The commonly used estimation techniques for the permeability function are reasonable for soils such as sands that experience little volume change as soil suction is changed. On the other hand, inaccurate results are generated when soils undergo volume change as is the case with oil sands tailings. Revisions to previous methodologies are proposed to render the estimation of the permeability function more suitable for simulating the drying process associated with soils that undergo high volume changes. The revised methodology independently analyzes the effect of volume changes (i.e., changes in void ratio) and degree of saturation changes (i.e., changes in S-SWCC (degree of saturation - soil-water characteristic curve)). Laboratory data on thickened oil sands tailings are presented and interpreted within the context of the proposed methodology.

Abstract:The unsaturated permeability function is an important soil property function used in the numerical modeling of saturated-unsaturated soil systems. The permeability function is generally predicted by integrating along the soil-water characteristic curve (SWCC) starting at saturated soil conditions. The integration is based on a particular integral formula. The Fredlund-Xing-Huang permeability function is a flexible integration technique used for calculating the unsaturated permeability function. The original permeability theory published by Fredlund, Xing, and Huang in 1994 specified that the air-entry value (AEV), aev , be used as the lower limit of the integration when calculating the permeability function. However, as there was no analytical procedure available for the calculation of the AEV on the SWCC, it became common practice to start the integration procedure from a value near zero. The assumption was made that the error associated with starting the integration from an arbitrary low value was minimal. While this might be the case in some situations, the error can be quite substantial in other situations. This paper undertakes a study of the effect of the lower limit of integration on the calculation of the permeability function. Comparisons are made between starting the integration from various values below the AEV and starting the integration from the calculated AEV, aev . A mathematical algorithm is also proposed for the calculation of the AEV for integration purposes. The results show that the relative coefficient of permeability can be significantly underestimated when the lower limit of integration is smaller than the AEV. The recommendation is that the AEV always be used as the lower limit of integration in the Fredlund-Xing-Huang permeability equation.Key words: permeability function, unsaturated coefficient of permeability, soil suction, unsaturated soil property functions, air-entry value.Résumé : La fonction de perméabilité non saturée est une fonction importante définissant les propriétés du sol et utilisée dans la modélisation numérique de systèmes de sols saturés et insaturés. On prédit habituellement la fonction de perméabilité en intégrant à la modélisation la courbe caractéristique sol-eau (CCSE) dans les conditions correspondant à celles d'un sol saturé. Cette intégration est basée sur une formule intégrale particulière. La fonction de perméabilité de Fredlund-Xing-Huang est une méthode souple d'intégration utilisée pour calculer la fonction de perméabilité non saturée. La théorie originale de perméabilité publiée par Fredlund, Xing et Huang en 1994 spécifiait que la valeur d'entrée d'air (VEA), aev , doit servir de limite inférieure de l'intégration lors du calcul de la fonction de perméabilité. Cependant, étant donné qu'il n'existait aucune procédure analytique disponible pour effectuer le calcul de la VEA sur la CCSE, il est devenu courant de commencer la procédure d'intégration à partir d'une valeur proche de zéro. On émit l'hypothèse que l'erreur associée au fait que l'on co...

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