Engineers Australia

Pitfalls in the Interpretation of Water Content Based Soil Water Characteristic Curve for Unsaturated Soils

Professor Nasser Khalili


The soil water characteristic curve (SWCC) is one of the most fundamental relationships in the mechanics of unsaturated soils. It enters calculations relating to deformation, shear strength, effective stress, fluid flow, water retention, drainage, water balance, and appears explicitly in the constitutive formulations of pore-air and pore-water, satisfying pore-phase volume change compatibility for a change in suction. More research effort has expended on the quantification and understanding of the water retention behaviour of unsaturated soils than any other phenomenon in the mechanics of unsaturated porous media.

Nevertheless, significant errors are frequently encountered in the interpretation and the use SWCC in the geotechnical engineering literature. In this presentation, pitfalls in the current approaches to determination of soil parameters form SWCC from the experimental data are highlighted. Special attention is given to the evaluation of the air entry value (AEV) from the water content based SWCC as well as the evolution of SWCC with void ratio. A consistent graphical approach is presented for the interpretation of SWCC taking into account the effects of stress history and volume change. The approach proposed is based solely on the experimental gravimetric water content-suction data without the need for volume change measurements during SWCC tests. In addition, a closed form solution is presented for the evolution of SWCC with void ratio. The robustness and application of the approaches proposed are demonstrated using extensive of experimental data.

About Professor Nasser Khalili

Professor Khalili has extensive experience in the field of geotechnical engineering both as a consultant and as an academic/researcher for more than 25 years. Prior to joining The University of New South Wales in 1993, Professor Khalili was responsible for managing the geotechnical group in the Chicago Office of the consulting firm Dames & Moore. He is currently the President of the Australian Association for Computational Mechanics (AACM), a member of the Institution of Engineers Australia, and a member of Australian Geomechanics Society. He is also a core member of the International Technical Committee on Unsaturated Soil (TC106). Professor Khalili’s research interests lie primarily in the areas of mechanics of unsaturated soils, soil plasticity, and mechanics of multi phase multi porous media.

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