Characterizing Liquid Phase Fabric of Unsaturated Specimens from X-Ray Computed Tomography Images

Pore-water in the funicular and pendular saturation regimes of the SWCC (Sr < 90%) assumes a complex fabric consisting of saturated pockets of water under negative pressure and a network of liquid bridges formed from menisci at the contact points of particles. Measurement and characterization of this liquid fabric for unsaturated soil assemblies over a range of saturation, stress, and deformation plays a pivotal role in improving our fundamental understanding of unsaturated soil behavior. However, lack of microstructural visualization techniques has hindered the consideration of liquid fabric distribution and evolution in macroscale geotechnical formulations. In this study X-ray CT scanning was used to monitor the changes in the liquid fabric of unsaturated glass beads. Images showing the three distinct phases of unsaturated specimens were successfully obtained. A computer code that automatically analyzes multiple images to quantify the components of a second-order fabric tensor was developed and applied to CT images obtained along the drying and wetting paths of a SWCC determined by digital image processing. Principal values, principal directions and invariants are quantified and implications of the changes to better description of unsaturated soil behavior are discussed.

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