17:15 〜 18:30
[AGE27-P12] 土壌空気が間隙ネットワーク特性および物質移動に及ぼす影響
キーワード：間隙ネットワーク、物質輸送、X-ray CT
Soil is a three-phase structure consisting of solids, liquids (water), and air. Volume and geometry soil air phase in soils affects network of water and air filled pores, then mass transport through the network. X-ray CT device is a strong tool for characterizing water-filled and air-filled soil pore networks, i.e., pore network properties such as pore size distributions, connectivity, or tortuosity in liquid and air phases. The purpose of this study is to clarify the effect of volume and geometry of soil air (entrapped or continuous air) on the pore network properties and mass transport.
Toyoura sand (mean dia. D50: 240 μm), Mikawa silica sand No. 7 (Mikawa-S, D50: 180 μm), and Mikawa silica sand No. 56 mixed with Mikawa-S (Mikawa-L, D50: 290 μm), were repacked to the acrylic or stainless column to make porous medias. Fully-saturated samples were prepared by repacking the sands under water saturation. Two different quasi-saturated samples were prepared either by repacking the sands in hydrogen peroxide solution (H2O2 samples) or re-saturating the samples after draining fully-saturated samples with -70 cm H2O water pressure (re-saturated samples). Unsaturated samples containing continuous air phase were prepared by stepwise drying or wetting.
The saturated and quasi-saturated hydraulic conductivity were measured by falling-head method, and the unsaturated hydraulic conductivity was measured by pressure control method. For unsaturated samples, gas diffusion coefficient was measured by diffusion chamber method and air permeability was calculated from the applied air pressure difference and flow rate to the soil sample by ventilating the samples.
The X-ray CT device (Carl Zeiss METROTOM 1500, voxel size: 10 μm) was used to take X-ray CT images of each sample for fully- and quasi-saturated and unsaturated conditions. The tortuosity (τ), pore coordination number (C), and pore size distribution in the gas or liquid phase were calculated from X-ray CT image analysis using of EX Fact Analysis (Nihon Visual Science, Japan).
Lower hydraulic conductivity was obtained for the H2O2 sample than for the re-saturated sample for the same volumetric water content. As results of X-ray CT image analysis, finer entrapped air existed in the liquid filled pore space for the H2O2 samples, resulting in the reduction on the liquid-phase pore connectivity. For the unsaturated samples with the presence of continuous air phase, no hysteresis was found in the relationship between hydraulic conductivity and volumetric water content, but hysteresis was found in the relationships between air permeability and gas diffusion coefficient and volumetric air content. Higher air permeability and gas diffusion at the wetting process were obtained than those at the drying process especially for the fine samples (Toyoura sand and Mikawa-S). The X-ray CT image analysis suggested that small pores located between large pores are active for air transport in the wetting process, creating continuous large pore networks in continuous air phases.
Toyoura sand (mean dia. D50: 240 μm), Mikawa silica sand No. 7 (Mikawa-S, D50: 180 μm), and Mikawa silica sand No. 56 mixed with Mikawa-S (Mikawa-L, D50: 290 μm), were repacked to the acrylic or stainless column to make porous medias. Fully-saturated samples were prepared by repacking the sands under water saturation. Two different quasi-saturated samples were prepared either by repacking the sands in hydrogen peroxide solution (H2O2 samples) or re-saturating the samples after draining fully-saturated samples with -70 cm H2O water pressure (re-saturated samples). Unsaturated samples containing continuous air phase were prepared by stepwise drying or wetting.
The saturated and quasi-saturated hydraulic conductivity were measured by falling-head method, and the unsaturated hydraulic conductivity was measured by pressure control method. For unsaturated samples, gas diffusion coefficient was measured by diffusion chamber method and air permeability was calculated from the applied air pressure difference and flow rate to the soil sample by ventilating the samples.
The X-ray CT device (Carl Zeiss METROTOM 1500, voxel size: 10 μm) was used to take X-ray CT images of each sample for fully- and quasi-saturated and unsaturated conditions. The tortuosity (τ), pore coordination number (C), and pore size distribution in the gas or liquid phase were calculated from X-ray CT image analysis using of EX Fact Analysis (Nihon Visual Science, Japan).
Lower hydraulic conductivity was obtained for the H2O2 sample than for the re-saturated sample for the same volumetric water content. As results of X-ray CT image analysis, finer entrapped air existed in the liquid filled pore space for the H2O2 samples, resulting in the reduction on the liquid-phase pore connectivity. For the unsaturated samples with the presence of continuous air phase, no hysteresis was found in the relationship between hydraulic conductivity and volumetric water content, but hysteresis was found in the relationships between air permeability and gas diffusion coefficient and volumetric air content. Higher air permeability and gas diffusion at the wetting process were obtained than those at the drying process especially for the fine samples (Toyoura sand and Mikawa-S). The X-ray CT image analysis suggested that small pores located between large pores are active for air transport in the wetting process, creating continuous large pore networks in continuous air phases.