Using Synchrotron-Based X-Ray Microcomputed Tomography to Characterize Water Distribution in Compacted Soils

Abstract

Water plays a vital role on the hydromechanical behavior of unsaturated soils. An important concern in unsaturated soil mechanics is to determine the distribution of water within voids and its interaction with soil grains. This paper presents some results of the spatial distribution of water in different soils using the synchrotron-based X-ray microcomputed tomography (μ-CT). Three materials (glass beads, natural sand, and clay) were first prepared at a water content of about 10%, statically compacted 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 (3D) microstructure of the samples including air, liquid, and solid phases was reconstructed, and some new observations were obtained: (i) the iodine-based contrast medium (KI) can increase the peak greyscale value of water from 110 to 122, enhance the air-water contrast, and thus facilitate the segmentation of water phase; (ii) in the compacted glass beads and sand, water distribution is characterized using the μ-CT and image reconstruction technique. The water contents obtained by phase segmentation, 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 glass beads and sand, respectively; (iii) water is preferably distributed within aggregates when it is mixed with the oven-dried particles, and an aggregate-dominated 3D structure is observed. However, it is impossible to determine the water phase for the studied material even with the resolution of 0.65 μm/pixel.

Microstructure Evolution of Hydrate‐Bearing Sands During Thermal Dissociation and Ensued Impacts on the Mechanical and Seepage Characteristics

“…Moreover, a part of the dissociated water and gas would migrate to the upper part of the specimen during the secondary hydrate formation. The uneven distribution of pore water vertically causes an uneven distribution of suction force, and this will lead to an uneven distribution of “false cohesion” throughout the specimen and weak the capacity to resist deformation in the lower part of the specimen (Fredlund et al, 1996; Li & Tang, 2019; Perera et al, 2011).…”

Discussion of “Unified Effective Stress Equation for Soil” by Chao Zhang and Ning Lu

“…The discussers, of course, acknowledge the challenges that the resolution issue and the representativeness of sample size at the same time may bring about when inspecting the finegrained material behavior. That is why a novel and multiphysics experiment would be required (Carminati et al 2007;Li and Tang 2019).…”

Review of Microfluidic Devices and Imaging Techniques for Fluid Flow Study in Porous Geomaterials

“…Improvements in data collection and processing have resulted in developing fast lab-based X-ray micro-tomography systems (X-ray µCT). Synchrotron radiation is electromagnetic radiation that is emitted when accelerated charged particles (with an speed close to the speed of light) are forced to change direction by a magnetic field [ 193 , 194 , 195 ]. Recent advances in synchrotron imaging allow spatial and temporal imaging of dynamic processes such as fluid displacement in porous media [ 195 , 196 ].…”