68th Canadian Geotechnical Conference and 7th Canadian Permafrost Conference

ROLE OF AIR-ENTRY VALUE AND CHOICE OF SWCC IN THE PREDICTION OF THE UNSATURATED PERMEABILITY

Session: Soil Mechanics III / Mécanique des sols III

Feixia Zhang, University of Alberta (Canada)
Delwyn Fredlund, Golder Associates Ltd, Saskatoon (Canada)
Murray Fredlund, SoilVision System Ltd. (Canada)
Ward Wilson, University of Alberta (Canada)

The permeability function is commonly estimated by integrating along the soil-water characteristic curve (SWCC) based on a particular integral formula. The Fredlund, Xing and Huang (1994) permeability function is a commonly used estimation technique. It has become common practice to start the integration procedure from a value near zero rather than the originally specified air-entry value (AEV). This paper undertakes a study on the effect of the lower limit of integration on the estimation of the permeability function. A mathematical algorithm is also proposed for the calculation of the AEV for integration purposes. The results reveal that the relative coefficient of permeability can be significantly under-estimated if 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 when using the Fredlund et al (1994) permeability estimation equation.