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 (d 50) 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 (D P/D 0), and permeability (k a) 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 (
), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between k a and d 50/T UMS 2, indicating a strong dependency of k a on mean particle size and direct correlation with gas diffusivity. Tortuosity (T MFX) and equivalent pore diameter (d eq.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 T UMS values showed reasonably good agreement with T MFX values. The k a showed a strong relationship when plotted against d eq.MFX/T MFX 2, indicating its strong dependency on pore size distribution and tortuosity of pore space.
1Department of Agroecology, Faculty of Science and Technology, Aarhus University, Tjele, Denmark. Dr. Muhammad Naveed is corresponding author.
2Department of Civil and Environmental Engineering, Saitama University, Saitama, Japan.
3Institute for Environmental Science and Technology, Saitama University, Saitama, Japan.
4Center for Experimental Study of Subsurface Environmental Processes, Colorado School of Mines, Golden, CO.
5Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
6Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark.
7School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR.
8Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX.
Address for correspondence: Dr. Muhammad Naveed, Department of Agroecology, Faculty of Science and Technology, Aarhus University, Blichers Allé 20, Postbox 50, DK-8830 Tjele, Denmark; E-mail: Muhammad.Naveed@agrsci.dk
Financial Disclosures/Conflicts of Interest: This work was supported by a research grant from the Innovative Research Organization, Saitama University; a research grant from the JST/JICA Science and Technology Research Partnership for Sustainable Development (SATREPS); the large framework project Soil Infrastructure, Interfaces, and Translocation Processes in Inner Space (Soil-it-is) funded by the Danish Research Council for Technology and Production Sciences; and Core Research Evolutionary Science and Technology (CREST) from Japan Science and Technology Agency (JST).
Received June 6, 2012.
Accepted for publication January 15, 2013.