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  • Hamamoto, Shoichiro  (29)
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  • 1
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(5), pp.1509-1517
    Description: The gas diffusion coefficient (Ds,g) and solute diffusion coefficient (D(s,l)) and their dependencies on fluid content (κ) (equal to soil–air content θ for D(s,g) and soil–water content ɛ for D(s,l)) are controlling factors for gas and solute transport in variably saturated soils. In this study, we propose unified, predictive models for D(s,g)(ɛ) and D(s,l)(θ) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid-induced reduction term including a percolation threshold (ɛ(th) for D(s,g) and θ(th) for D(s,l)). Different percolation threshold terms adopted from recent studies for gas (D(s,g)) and solute (D(s,l)) diffusion were applied. For gas diffusion, ɛth was a function of bulk density (total porosity), while for solute diffusion θ(th) was best described by volumetric content of finer soil particles (clay and organic matter), FINES(vol). The resulting LIquid and GAs diffusivity and tortuosity (LIGA) models were tested against D(s,g) and D(s,l) data for differently-textured soils and performed well against the measured data across soil types. A sensitivity analysis using the new Maxwell’s Law based LIGA models implied that the liquid phase but not the gaseous-phase tortuosity was controlled by soil type. The analyses also suggested very different pathways and fluid-phase connectivity for gas and solute diffusion in unsaturated soil. In conclusion, the commonly applied strategy of using the same, soil-type-independent model for gas and solute diffusivity in analytical and numerical models for chemical transport and fate in variably-saturated soils appears invalid, except for highly sandy soils. The unified LIGA model with differing percolation thresholds for diffusion in the liquid and gaseous phases solves this problem. ; p. 1509-1517.
    Keywords: Clay ; Sandy Soils ; Bulk Density ; Solutes ; Mathematical Models ; Organic Matter ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 2
    Language: English
    In: Water Research, 01 May 2016, Vol.94, pp.120-127
    Description: Global warming and urbanization together with development of subsurface infrastructures (e.g. subways, shopping complexes, sewage systems, and Ground Source Heat Pump (GSHP) systems) will likely cause a rapid increase in the temperature of relatively shallow groundwater reservoirs (subsurface thermal pollution). However, potential effects of a subsurface temperature change on groundwater quality due to changed physical, chemical, and microbial processes have received little attention. We therefore investigated changes in 34 groundwater quality parameters during a 13-month enhanced-heating period, followed by 14 months of natural or enhanced cooling in a confined marine aquifer at around 17 m depth on the Saitama University campus, Japan. A full-scale GSHP test facility consisting of a 50 m deep U-tube for circulating the heat-carrying fluid and four monitoring wells at 1, 2, 5, and 10 m from the U-tube were installed, and groundwater quality was monitored every 1–2 weeks. Rapid changes in the groundwater level in the area, especially during the summer, prevented accurate analyses of temperature effects using a single-well time series. Instead, Dual-Well Analysis (DWA) was applied, comparing variations in subsurface temperature and groundwater chemical concentrations between the thermally-disturbed well and a non-affected reference well. Using the 1 m distant well (temperature increase up to 7 °C) and the 10 m distant well (non-temperature-affected), the DWA showed an approximately linear relationships for eight components (B, Si, Li, dissolved organic carbon (DOC), Mg , NH , Na , and K ) during the combined 27 months of heating and cooling, suggesting changes in concentration between 4% and 31% for a temperature change of 7 °C.
    Keywords: Subsurface Thermal Pollution ; Ground Source Heat Pump (Gshp) Systems ; Long-Term Heating and Cooling ; Confined Marine Aquifer ; Dual-Well Analysis (Dwa) ; Groundwater Quality ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 3
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(3), pp.795-806
    Description: The air permeability (ka) and soil gas diffusion coefficients (Dp) are controlling factors for gas transport and fate in variably saturated soils. We developed a unified model for ka and Dp based on the classical Archie's law, extended by: (i) allowing for two-region gas transport behavior for structured soils, with the natural field moisture condition (set at −100 cm H2O matric potential [pF 2]) as the reference (spliced) point between the large-pore (drained pore diameter ≥30 μm at pF ≤ 2) and the small-pore (subsequently drained pores 2) regions, and (ii) including a percolation threshold, set as 10% of the total porosity for structureless porous media or 10% of the porosity in the large-pore region for structured soils. The resulting extended Archie's law with reference point (EXAR) models for ka and Dp were fitted to the measured data. For both structureless and structured porous media, Archie's saturation exponent (n) was higher for Dp than for ka, indicating higher water blockage effects on gas diffusion. For structured soils, the saturation exponent for the large-pore region (n1) was lower than for the small-pore region (n2). Generally, n1 values of∼1 for ka and 2 for Dp and n2 values of 4/3 for ka and 7/3 for Dp described the data well. Two reference-point expressions for ka at pF 2 were also developed and tested together with existing models for Dp at pF 2 against independent data across soil types. The best-performing reference-point models were a ka model based on the classical Kozeny equation and the Moldrup Dp model. ; p. 795-806.
    Keywords: Models ; Water ; Soil Air ; Soil Types ; Porous Media ; Air ; Equations ; Permeability ; Porosity ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 4
    Language: English
    In: Journal of Geotechnical and Geoenvironmental Engineering, July, 2011, Vol.137(7), p.653(10)
    Description: Landfill sites have been implicated in greenhouse warming scenarios as a significant source of atmospheric methane. In this study, the effects of extreme compaction on the two main soil-gas transport parameters, the gas diffusion coefficient ([D.sub.p]) and the intrinsic air permeability ([k.sub.a]), and the cumulative methane oxidation rate in a landfill cover soil were investigated. Extremely compacted landfill cover soil exhibited negligible inactive soil-air contents for both [D.sub.p] and ka. In addition, greater [D.sub.p] and [k.sub.a] were observed as compared with normal compacted soils at the same soil-air content ([epsilon]), likely because of reduced water-blockage effects under extreme compaction. These phenomena are not included in existing predictive models for [D.sub.p]([epsilon]) and ka([epsilon]). On the basis of the measured data, new predictive models for [D.sub.p]([epsilon]) and ka([epsilon]) were developed with model parameters (representing air-filled pore connectivity and water-blockage effects) expressed as functions of dry density ([[rho].sub.b]). The developed [D.sub.p] ([epsilon]) and [k.sub.a] (e) models together with soil-water retention data for soils at normal and extreme compaction ([[rho].sub.b] = 1.44 and 1.85 g [cm.sup.-3]) implied that extremely compacted soils will exhibit lower [D.sub.p] and [k.sub.a] at natural field-water content (-100 cm [H.sub.2]O of soil-water matric potential) because of much lower soil-air content. Numerical simulations of methane gas transport, including a first-order methane oxidation rate, were performed for differently compacted soils by using the new predictive [D.sub.p]([epsilon]) model. Model results showed that compaction-induced difference in soil-air content at a given soil-water matric potential condition is likely the most important parameter governing methane oxidation rates in extremely compacted landfill cover soil. DOI: 10.1061/(ASCE)GT.1943-5606.0000459. CE Database subject headings: Landfills; Coverings; Gas; Parameters; Methane. Author keywords: Landfill final cover soil; Gas transport parameters; Compaction.
    Keywords: Atmospheric Carbon Dioxide -- Analysis ; Waste Management -- Analysis ; Methane -- Analysis ; Permeability -- Analysis ; Natural Gas Transmission -- Analysis
    ISSN: 1090-0241
    E-ISSN: 19435606
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  • 5
    Language: English
    In: Waste Management, 2011, Vol.31(12), pp.2464-2472
    Description: ► The effects of soil physical properties on gas transport parameters were investigated. ► Higher values of and exhibited in the ‘+gravel’ than the ‘−gravel’ fraction at same soil–air content ( ). ► Recent power law models for (WLR) and (RPL) were modified. ► Model parameters were linearly related to easily measurable dry bulk density ( ). Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, , and particle size fraction on the main soil–gas transport parameters – soil–gas diffusivity ( / , ratio of gas diffusion coefficients in soil and free air) and air permeability ( ) – under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting values ranging from 1.40 to 2.10 g cm . Results showed that and values for the ‘+gravel’ fraction (〈35 mm) became larger than for the ‘−gravel’ fraction (〈2 mm) under variably-saturated conditions for a given soil–air content ( ), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on and was most pronounced for the ‘+gravel’ fraction. Normalized ratios were introduced for all soil–gas parameters: (i) for gas diffusivity / , the ratio of measured to in total porosity ( ), (ii) for air permeability / , the ratio of measured to at 1235 kPa matric potential (=pF 4.1), and (iii) for soil–air content, the ratio of soil–air content ( ) to total porosity ( ) (air saturation). Based on the normalized parameters, predictive power-law models for ( / ) and ( / ) models were developed based on a single parameter (water blockage factor for and for ). The water blockage factors, and , were found to be linearly correlated to values, and the effects of dry bulk density on and for both ‘+gravel’ and ‘−gravel’ fractions were well accounted for by the new models.
    Keywords: Air Permeability ; Gas Diffusivity ; Dry Bulk Density ; Landfill Final Cover ; Engineering ; Chemistry
    ISSN: 0956-053X
    E-ISSN: 1879-2456
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  • 6
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Gas diffusion is a dominant transport mechanism for climate and regulated gases in the vadose zone. Soil-gas diffusion is governed by the gas diffusion coefficient (D (sub p) , m (super 2) s (super -1) ) which is highly dependent on soil texture, such as sand, silt, clay, and organic matter contents, as well as soil physical properties such as soil-air content (epsilon , m (super 3) m (super -3) ) or total porosity (Phi , m (super 3) m (super -3) ). Soil organic matter is a key contributor to the formation of the soil pore structure (i.e., total porosity and air-filled pore tortuosity), and it highly affects D (sub p) behavior under variably saturated conditions. In this study, based on numerous D (sub p) data sets across soil types including sands, loamy clay soils, volcanic ash soils, and organic soils, predictive D (sub p) models incorporating a percolation threshold (epsilon (sub th) , m (super 3) m (super -3) ) and pore tortuosity factor (X') are proposed. The observed relations between either epsilon (sub th) or X' and either Phi or volumetric organic matter fraction (OMF, m (super 3) m (super -3) ) were embedded in the proposed D (sub p) model. The proposed D (sub p) models, coupled with predictive epsilon (sub th) and OMF models, performed well against the measured D (sub p) data across soil types. Finally, a sensitivity analysis of the OMF in relation to the D (sub p) and pore-network tortuosity (T) showed a reduction in D (sub p) and increase in T with increasing OMF under the same epsilon conditions.
    Keywords: Soils ; Asia ; Diffusion ; Far East ; Gases ; Grain Size ; Hokkaido ; Honshu ; Hydrology ; Japan ; Loam ; Memuro Japan ; Moisture ; Nishi-Tokyo Japan ; Organic Compounds ; Percolation ; Permeability ; Physical Properties ; Porosity ; Power Law ; Saitama Japan ; Saturation ; Size Distribution ; Soil Gases ; Soils ; Statistical Analysis ; Tortuosity ; Transport ; Unsaturated Zone ; Volcanic Soils ; Water;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 7
    Language: English
    In: Soil Science Society of America Journal, March, 2013, Vol.77(2), p.362(10)
    Description: Understanding soil-gas phase properties and processes is important for finding solutions to critical environmental problems such as greenhouse gas emissions and transport of gaseous-phase contaminants in soils. Soil-air permeability, ka (?m2), is the key parameter governing advective gas movement in soil and is controlled by soil physical characteristics representing soil texture and structure. Models predicting ka as a function of air-filled porosity (?) often use a reference-point measurement, for example, ka,1000 at ?1000 (where the measurement is done at a suction of -1000 cm H2O). Using ka measurements from two Danish arable fields, each located on natural clay gradients, this study presents a pore tortuosity-disconnectivity analysis to characterize the soil-gas phase. The main objective of this study is to investigate the effect of soil-moisture condition, clay content, and other potential drivers of soil texture and structure on soil-gas phase characteristics based on a ka-based pore tortuosity parameter, Xa [= log(ka/ka,1000)/log(?/?,1000)]. Results showed that Xa did not vary significantly with soil matric potential (in the range of -10 to -1000 cm H2O), but the average Xa across moisture conditions showed a strong linear relation (R2 = 0.74) to clay content. The Xa, further showed promising relations to specific surface area, Rosin-Rammler particle size distribution indices, ? and ? (representing characteristic particle size and degree of sorting, respectively), and the Campbell water retention parameter, b. Considering clay as a main driver of soil-gas phase characteristics, we developed expressions linking clay content and ka,1000 at ?1000 and discussed the effect of clay content on general ka-? behavior.
    Keywords: Grading (Building materials) -- Usage ; Soil Permeability -- Analysis ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 8
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(3), pp.845-852
    Description: Subsurface gaseous-phase transport is governed by three gas transport parameters: the air permeability coefficient (k(a)), gas diffusion coefficient (D(P)), and gas dispersion coefficient (D(H)). Among these, D(H) is the least understood due to hitherto limited research into the relationship between gas dispersion and soil physical characteristics. In this study, a series of advection-dispersion experiments was performed on granular porous media to identify the effects of soil column dimensions (length and diameter), particle size and shape, dry bulk density, and moisture content on the magnitude of gas dispersion. Glass beads and various sands of different shapes (angular and rounded) with mean particle diameters (d(50)) ranging from 0.19 to 1.51 mm at both air-dry and variable moisture contents were used as granular porous media. Gas dispersion coefficients and gas dispersivities (α = D(H)/v, where v is the pore-gas velocity) were determined by fitting the advection-dispersion equation to the measured breakthrough curves. For all test conditions, D(H) increased linearly with v. The test results showed that neither soil column length nor diameter had significant effect on gas dispersivity. Under air-dry conditions, higher gas dispersivities were observed for media with wider particle size distribution and higher dry bulk density. The minor effect of particle shape on gas dispersivity was found under both air-dry and wet conditions. Under wet conditions, the variations in gas dispersivity were mainly controlled by the air-filled porosity. An empirical model was also proposed for the prediction of gas dispersivity in granular, unsaturated porous media. ; p. 845-852.
    Keywords: Soil Physical Properties ; Particle Size ; Sand ; Bulk Density ; Porous Media ; Prediction ; Equations ; Porosity ; Models ; Glass ; Water Content ; Air ; Permeability ; Particle Size Distribution ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Soils and Foundations, August 2016, Vol.56(4), pp.676-690
    Description: Mass transport in soils occurs through pore networks that are highly affected by basic physical properties such as the degree of compaction, and particle size and shape. In this study, micro-focus X-ray computed tomography (CT) was used to obtain information on the pore network structure at different compaction levels for repacked columns of sands and glass beads representing different size fractions and particle shapes. Mass transport parameters, including gas diffusion coefficient ( ) and air permeability ( ) at variably saturated conditions, were measured on the same columns using standard methods, and literature data on saturated hydraulic conductivity ( ) for the same materials were analyzed. A comparison of X-ray CT derived pore network structure and physical parameters showed that the round sands and glass beads exhibited larger pores, a higher pore coordination number, and a lower volumetric surface area than that of angular sands at the same particle size, resulting in higher as well as higher and under relatively dry conditions. The X-ray CT derived the mean pore diameter ( ), and the pore coordination number ( ) for each material correlated well with key gas transport properties such as percolation thresholds and pore network connectivity. A predictive model from wet to dry conditions based fully on X-ray CT derived parameters ( and ) was developed and showed good agreement with measured for both round and angular sands.
    Keywords: Micro-Focus X-Ray CT ; Pore Structure ; Mass Transport Parameters ; Engineering
    ISSN: 0038-0806
    Source: ScienceDirect Journals (Elsevier)
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  • 10
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Soil thermal conductivity (lambda ) and heat capacity (C) control heat transport and the thermal environment for biogeophysical processes in the vadose zone. Accurate lambda and C predictions for peaty soils with high organic contents are particularly important for assessing emissions of greenhouse gases formed during microbial activity in wetlands. In this study, we measured the lambda and C at different soil-water matric potentials on undisturbed samples for three peaty soil profiles at the Hokkaido Bibai marsh in Japan, representing a total of 10 different soil horizons. The thermal properties under air-dried conditions, lambda (sub dry) and C (sub dry) , were measured separately at changing volumetric solids contents (sigma ). For each sample, volume shrinkage was observed to varying degrees during the drying process. Measured lambda and C increased linearly with increasing volumetric water content (theta ). Applying the concept of a three-phase mixing model and incorporating the lambda -theta or C-theta and the lambda (sub dry) -sigma or C (sub dry) -sigma relations, predictive lambda and C models were developed as functions of sigma and theta . The new mixing model is represented by lambda = lambda (sub dry) +f (sub lambda ) theta lambda (sub w) and C = C (sub dry) +f (sub C) {theta}C (sub w) , where lambda (sub w) and C (sub w) are the thermal conductivity and heat capacity of water, respectively, and f is an impedance factor that takes into account the liquid-phase tortuosity. The new mixing model predicted literature lambda -theta data on peaty and highly organic soils under variable saturation well. The probable ranges of lambda and C under variable saturation were proposed based on the sensitivity analysis.
    Keywords: Soils ; Asia ; Bibai Marsh ; Biogenic Processes ; Bogs ; Carbon ; Equations ; Far East ; Ground Water ; Heat Capacity ; Heat Flow ; Heat Transport ; Hokkaido ; Horizons ; Hydrologic Cycle ; Hydrology ; Impedance ; Japan ; Liquid Phase ; Mires ; Organic Carbon ; Peat ; Physicochemical Properties ; Retention ; Sediments ; Sensitivity Analysis ; Soils ; Statistical Analysis ; Thermal Conductivity ; Thermal Properties ; Transport ; Unsaturated Zone ; Water Table ; Wetlands;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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