Water plays a vital role on the hydromechanical behavior of unsaturated soils. An important concern in unsaturated soil\nmechanics is to determine the distribution of water within voids and its interaction with soil grains. This paper presents some\nresults of the spatial distribution of water in different soils using the synchrotron-based X-ray microcomputed tomography\n(micro-CT). Three materials (glass beads, natural sand, and clay) were first prepared at a water content of about 10%, statically\ncompacted under vertical total stress of 500 kPa, and then scanned by synchrotron X-rays at an energy of 18 or 20 keV. The three dimensional\n(3D) microstructure of the samples including air, liquid, and solid phases was reconstructed, and some new\nobservations were obtained: (i) the iodine-based contrast medium (KI) can increase the peak greyscale value of water from 110 to\n122, enhance the air-water contrast, and thus facilitate the segmentation of water phase; (ii) in the compacted glass beads and sand,\nwater distribution is characterized using the micro-CT and image reconstruction technique. The water contents obtained by phase\nsegmentation, i.e., 10.2% and 9.3%, are comparable with those measured by the oven-drying method, i.e., 9.7% and 9.4% for the\nglass beads and sand, respectively; (iii) water is preferably distributed within aggregates when it is mixed with the oven-dried\nparticles, and an aggregate-dominated 3D structure is observed. However, it is impossible to determine the water phase for the\nstudied material even with the resolution of 0.65 micro m/pixel.
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