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  • 1
    In: Soil Science, 2013, Vol.178(2), pp.60-68
    Description: ABSTRACT: Gas transport parameters and X-ray computed tomography (CT) measurements in porous medium under controlled and identical conditions provide a useful methodology for studying the relationships among them, ultimately leading to a better understanding of subsurface gaseous transport and other soil physical processes. The objective of this study was to characterize the relationships between gas transport parameters and soil-pore geometry revealed by X-ray CT. Sands of different shapes with a mean particle diameter (d50) ranging from 0.19 to 1.51 mm were used as porous media under both air-dried and partially saturated conditions. Gas transport parameters including gas dispersivity (α), diffusivity (DP/D0), and permeability (ka) were measured using a unified measurement system (UMS). The 3DMA-Rock computational package was used for analysis of three-dimensional CT data. A strong linear relationship was found between α and tortuosity calculated from gas transport parameters ((Equation is included in full-text article.)), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between ka and d50/TUMS, indicating a strong dependency of ka on mean particle size and direct correlation with gas diffusivity. Tortuosity (TMFX) and equivalent pore diameter (deq.MFX) analyzed from microfocus X-ray CT increased linearly with increasing d50 for both Granusil and Accusand and further showing no effect of particle shape. The TUMS values showed reasonably good agreement with TMFX values. The ka showed a strong relationship when plotted against deq.MFX/TMFX, indicating its strong dependency on pore size distribution and tortuosity of pore space.
    Keywords: Tomography ; Correlation Analysis ; Soil Permeability ; Measurement ; Porous Materials ; Pore Size;
    ISSN: 0038-075X
    E-ISSN: 15389243
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  • 2
    In: Soil Science, 2013, Vol.178(7), pp.359-368
    Description: ABSTRACT: The aim of this study was to articulate the potential of medical computed tomographic (CT) scanning for analyzing soil structure (macroporosity, soil matrix density, number of macropores) and how these estimates compare with, and complement, traditional laboratory measurements (bulk density, total porosity, effective air-filled porosity, and air permeability). Undisturbed soil cores were sampled at two depths (0.35 and 0.7 m) in a long-term soil compaction experiment in southern Sweden 14 years after its establishment. Persistence of subsoil compaction was detectable by CT-estimated soil matrix density, bulk density, and total porosity. Vertical distribution of CT-estimated air-filled macroporosity between 0.25- and 0.45-m depth showed that biological activity effect on macroporosity was largest in the top of the soil columns from the compacted plots, whereas reduction of macroporosity was significant at the bottom of the same columns. This was not detectable by classical laboratory measurements. Variations in air permeability could be related to the CT-estimated number of pores but not to the CT-estimated air-filled macroporosity. Despite using a coarse resolution, the combination of visualization and traditional laboratory measurements proved valuable in identifying the persistent effects of subsoil compaction and the differences in soil structure among the two investigated subsoil layers. However, we recommend to systematically perform a sensitivity analysis to the segmentation threshold before any further analysis of CT-estimated parameters.
    Keywords: Sweden ; Tomography ; X Rays ; Soil Testing ; Sensitivity Analysis ; Porosity;
    ISSN: 0038-075X
    E-ISSN: 15389243
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