2008 Joint Annual Meeting (5-9 Oct. 2008): Single- and Two-Individual-Region Models for Gas Diffusivity in Structureless or Aggregated, Unsaturated Soil.
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664-10 Single- and Two-Individual-Region Models for Gas Diffusivity in Structureless or Aggregated, Unsaturated Soil.



Tuesday, 7 October 2008
George R. Brown Convention Center, Exhibit Hall E
Augustus C. Resurreccion, Dep. of Engineering Sciences, University of the Philippines-Diliman, Quezon City, Philippines, Ken Kawamoto, JAPAN, Saitama University, Saitama University, 255 Shimo-okubo Sakura-ku, Saitama, JAPAN, Shoichiro Hamamoto, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan, Toshiko Komatsu, JAPAN, Saitama University, Saitama University, Shimo-okubo Sakura-ku, Saitama, 338-8570, JAPAN and Per Moldrup, DENMARK,Aalborg Univ., Dept. of Biotech. Chem. and Environ. Engineering, Aalborg Univ Sohngaardsholmsvej 57 D-building, Aalborg, DK9000, DENMARK
An accurate evaluation of the fate and transport of gaseous phase contaminants requires the understanding of gas diffusion coefficient (Dp) of soils as a function of soil-air content, e.  Recent studies have shown that the modality of the pore size distribution, as a result of soil structure, largely influence the magnitude of the soil-gas diffusivity (Dp/Do, where Do is the gas diffusion coefficient in free air) and its variation with e. In this study, flexible Dp/Do models for one-region (structureless) and two-region (aggregated or structured) soils were presented. For one-region soils, we modified the recently-developed Water-induced Linear Reduction (WLR) factor of Moldrup et al. (2000) to become a nonlinear description of water blocking effects of connected water films on soil-gas diffusion. This Water-induced Non-linear Reduction (WNR) Dp/Do model performs well for structureless soils ranging from sand to clay. For two-region soils, WNR factors were applied separately to a power-law model in the inter-aggregate pore space region and to a linear model in the intra-aggregate pore space region to become Two-Individual Region (TIR) Dp/Do model. This TIR model described well the Dp/Do of pure aggregates and highly structured soils at different compaction levels.  The impedance and tortuosity factors were observed to be almost constant in the intra-aggregate pore space region suggesting small water blocking effect that, in most cases, verified the observed linear variation of Dp/Do with e in the intra-aggregate region. By merely using standard parameter values for the TIR Dp/Do model and with the inter-aggregate porosity estimated as half of the total porosity, a better prediction of Dp/Do was observed within the total range of soil-air content than the widely-used classical Dp/Do models.
See more of: Emerging Soil Physical Processes and Properties: Colloid-, Water-, and Gas-Phases and Interphases: II (Posters)
See more of: S01 Soil Physics