Particle Size Segregation during Hand Packing of Coarse Granular Materials and Impacts on Local Pore‐Scale Structure

Lebron, Inma; Robinson, David A.

doi:10.2136/vzj2003.3300

Cited by 12 publications

(1 citation statement)

References 38 publications

(60 reference statements)

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“…hus, at static water table conditions, both columns showed highly comparable transport parameters. he minor diference between a L of the reference and the dynamic column was assumed to be due to packing (Lebron and Robinson, 2003). he dispersivities were in the same range as in other repacked column experiments where porous media of similar grain sizes were used (Mansell et al, 1977;Padilla et al, 1999;Bromly and Hinz, 2004).…”

Section: Solute Transportmentioning

confidence: 99%

Response of Transport Parameters and Sediment Microbiota to Water Table Fluctuations in Laboratory Columns

Rühle

Netzer

Lueders

et al. 2015

Vadose Zone Journal

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Groundwater table fluctuations create a dynamic interface between the unsaturated and saturated zone with spatially as well as temporally changing water content and water fluxes. Our objective was to investigate the impact of periodic water table fluctuations on transport parameters, geochemical gradients, and bacterial abundance and community structure in groundwater sediments. We conducted tracer experiments in one‐dimensional column systems investigating vertical flow with static or fluctuating water tables, constantly infiltrated with groundwater and model dissolved organic carbon (DOC). Pore water sampling was performed throughout the experiments, and sediment bacteria of both systems were characterized after completion of the experiment. Our results indicate that neither the longitudinal dispersivity nor column geochemistry was affected by the applied water table fluctuations. However, water content and flow velocities varied dynamically over time and depth in the fluctuation zone. Depth‐resolved bacterial community composition was clearly distinct, with additional populations detected especially in the fluctuation zone. These were absent in the static column, while overall bacterial diversity was similar over depth in both columns. We assume that spatial and temporal changes in water content and/or flow velocities were driving these microbial distinctions. This implies that complex feedback mechanisms between local hydrology and sedimentary bacterial communities in porous media exist. These results are important for the understanding of transformation and biodegradation processes at groundwater tables under increased hydraulic forcing.

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Section: Solute Transportmentioning

confidence: 99%

Response of Transport Parameters and Sediment Microbiota to Water Table Fluctuations in Laboratory Columns

Rühle

Netzer

Lueders

et al. 2015

Vadose Zone Journal

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Improved understanding of bimolecular reactions in deceptively simple homogeneous media: From laboratory experiments to Lagrangian quantification

et al. 2014

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Medium heterogeneity affects reaction kinetics by controlling the mixing of reactant particles, but the linkage between medium properties and reaction kinetics is difficult to build, even for simple, relatively homogeneous media. This study aims to explore the dynamics of bimolecular reactions, aniline 1 1,2-naphthoquinone-4-sulfonic acid ! 1,2-naphthoquinone-4-aminobenzene, in relatively homogeneous flow cells. Laboratory experiments were conducted to monitor the transport of both conservative and reactive tracers through columns packed with silica sand of specific diameters. The measured tracer breakthrough curves exhibit subdiffusive behavior with a late-time tail becoming more pronounced with decreasing sand size, probably due to the segregated flow regions formed more easily in columns packed with smaller size sand. Numerical analysis using a novel Lagrangian model shows that subdiffusion has a twofold effect on bimolecular reactions. While subdiffusion enhances the power-law growth rate of product mass by prolonging the exposure of reactant particles in the depletion zone, the global reaction rate is constrained because subdiffusion constrains the mobility of reactant particles. Reactive kinetics in deceptively simple homogeneous media is therefore controlled by subdiffusion, which is sensitive to the dimensions of packed sand.

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Using a pore‐scale model to quantify the effect of particle re‐arrangement on pore structure and hydraulic properties

Dikinya

Lehmann

Hinz

et al. 2007

Hydrological Processes

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Abstract:A pore-scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l 1 NaCl during leaching. This was applied to examine the effects of particle release and re-deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0Ð4% of the initial value and the air-entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8Ð5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore-size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 µm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 µm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve.

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Particle Size Segregation during Hand Packing of Coarse Granular Materials and Impacts on Local Pore‐Scale Structure

Cited by 12 publications

References 38 publications

Response of Transport Parameters and Sediment Microbiota to Water Table Fluctuations in Laboratory Columns

Response of Transport Parameters and Sediment Microbiota to Water Table Fluctuations in Laboratory Columns

Improved understanding of bimolecular reactions in deceptively simple homogeneous media: From laboratory experiments to Lagrangian quantification

Using a pore‐scale model to quantify the effect of particle re‐arrangement on pore structure and hydraulic properties

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