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  • 1
    Electronic Resource
    Electronic Resource
    Quantification of pore structure and gas diffusion as a function of scale (2002)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 53 (2002), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The quantification of the spatial heterogeneity of soil structure is one of the main difficulties to overcome for an adequate understanding of soil processes. There are different competing concepts for the type of heterogeneity, including macroscopic homogeneity, discrete hierarchy or fractal. With respect to these different concepts we investigate the structure of the pore space in one single sample (4 × 103 mm3) by analysing basic geometric quantities of the pores 〉 0.3 mm within gradually increasing subsamples. To demonstrate the relation between geometrical and functional properties we simulate gas diffusion within the three-dimensional pore space of the different subsamples. An efficient tool to determine the geometric quantities is presented. As a result, no representative elementary volume (REV) is found in terms of pore-volume density which increases with sample size. The same is true for the simulated gas diffusion coefficient. This effect is explained by two different types of pores, i.e. big root channels and smaller pores, having different levels of organization. We discuss the different concepts of structural organization which may be appropriate models for the structure investigated. We argue that the discrete hierarchical approach is the most profitable in practice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2002.00457.x
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  • 2
    Electronic Resource
    Electronic Resource
    Gas diffusion in a silty-clay soil: experimental study on an undisturbed soil core and simulation in its three-dimensional reconstruction (1999)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 50 (1999), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Transport of gas in soil depends on the paths available through the porous system. We determined the rate of diffusion of air through a core of silty-clay soil experimentally. After the experiment, the core was impregnated with resin and sectioned at 100 μm. From the images of the sections, the porous structure was reconstructed in three dimensions with a 100-μm resolution and gas diffusion was simulated in it. We computed the self-diffusion to describe gas diffusion. The experiment and simulation were compared using tortuosity, which is the ratio between the self-diffusion coefficient calculated in air and the coefficient calculated in the reconstructed sample. The results showed that the experimentally measured tortuosity (2.3) and the numerically calculated tortuosity (1.75) were similar. This suggests that the self-diffusion propagator is useful for simulating self-diffusion in a numerical three-dimensional reconstructed sample and that the scale chosen for the reconstruction of the sample (100 μm) was suitable for this particular soil. Résumé Les propriétés de transfert en phase gazeuse des sols ont étéétudiées sur un sol limono-argileux. A l’issue de l’expérience, l’échantillon a été imprégné avec une résine polyester puis sectionné en coupes sériées. A l’aide des images numérisées des coupes, l’échantillon a été reconstruit en trois dimensions. Nous avons ensuite simulé le processus de diffusion gazeuse dans l’échantillon reconstruit à l’aide du propagateur de diffusion. Expérience et simulation ont été comparées à l’aide de la tortuosité, rapport entre le coefficient de diffusion gazeuse dans l’air et celui dans le sol. Les résultats montrent que la tortuosité mesurée expérimentalement (2,3) et la tortuosité calculée numériquement (1,75) sont proches. Ceci prouve que l’utilisation du propagateur de diffusion est justifiée pour la simulation du processus de self-diffusion dans un échantillon tridimensionnel reconstruit et que l’échelle choisie pour la reconstruction (100 μm) s’avère pertinente pour l’étude de la diffusion gazeuse dans ce sol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1999.00215.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of compaction on the porosity of a silty soil: influence on unsaturated hydraulic properties (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 52 (2001), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Tillage and traffic modify soil porosity and pore size distribution, leading to changes in the unsaturated hydraulic properties of the tilled layer. These changes are still difficult to characterize. We have investigated the effect of compaction on the change in the soil porosity and its consequences for water retention and hydraulic conductivity. A freshly tilled layer and a soil layer compacted by wheel tracks were created in a silty soil to obtain contrasting bulk densities (1.17 and 1.63 g cm−3, respectively). Soil porosity was analysed by mercury porosimetry, and scanning electron microscopy was used to distinguish between the textural pore space and the structural pore space. The laboratory method of Wind (direct evaporation) was used to measure the hydraulic properties in the tensiometric range. For water potentials 〈 −20 kPa, the compacted layer retained more water than did the uncompacted layer, but the relation between the hydraulic conductivity and the water ratio (the volume of water per unit volume of solid phase) was not affected by the change in bulk density. Compaction did not affect the textural porosity (i.e. matrix porosity), but it created relict structural pores accessible only through the micropores of the matrix. These relict structural pores could be the reason for the change in the hydraulic properties due to compaction. They can be used as an indicator of the consequences of compaction on unsaturated hydraulic properties. The modification of the pore geometry during compaction results not only from a decrease in the volume of structural pores but also from a change in the relation between the textural pores and the remaining structural pores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2001.00357.x
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  • 4
    Electronic Resource
    Electronic Resource
    Three-dimensional crack monitoring by electrical resistivity measurement (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    European journal of soil science 55 (2004), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Soil cracks formed by natural processes play a key role in water and gas transfer. Patterns of soil cracks are, however, difficult to characterize. Our aim here is to assess the effectiveness of three-dimensional electrical resistivity surveys in detecting soil crack networks. A three-dimensional electrical survey was carried out by a square array quadripole with Cu–CuSO4 electrodes (electrode spacing of 3 cm). The measurements were made with two orientations (0° and 90°) on a block (26 cm × 30 cm × 40 cm) of soil while it dried for 18 days under controlled conditions. Two indexes, calculated from the apparent resistivity values, were evaluated to detect the degree of soil heterogeneity: (i) an anisotropy index based on the ratio between the apparent resistivity at 0° and that at 90°; and (ii) the angle-array orientation corresponding to the preferential anisotropic orientation (maximum resistivity). The anisotropy index provided information on the presence of cracks and the orientation for crack width 〉 1 mm in the first pseudo-depth (i.e. depth of investigation), while the angle-array orientation provided information on crack extension for the whole pseudo-depth. Information about the presence, position, orientation and extension of cracks can be obtained from an analysis of apparent resistivity obtained by a three-dimensional electrical survey. Such direct analysis will help the resistivity inversion to detect the crack network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2004.00632.x
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  • 5
    Electronic Resource
    Electronic Resource
    Variation of textural porosity of a clay-loam soil during compaction (1995)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 46 (1995), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effect of compaction on the porosity of aggregates was studied in the laboratory using mercury porosimetry and backscattered electron scanning images (BESI) of polished thin sections. Porosity was divided into structural and textural porosity, and then textural porosity into lacunar and clayey porosity.For aggregates equilibrated at a water potential of −1 kPa and pressures of 50 and 200 kPa, compaction of structural porosity resulted in an increase of textural porosity. For aggregates equilibrated at a water potential of −1 kPa and an applied pressure of 600 kPa, the structural porosity strongly decreased but did not result in a variation of textural porosity. For aggregates equilibrated at water potentials of −63 and −103 kPa and the three values of pressure studied, textural porosity was unaffected by compaction whatever the evolution of structural porosity. The BESI indicated that the increase in textural porosity which was recorded by mercury porosimetry for aggregates equilibrated at a water potential of −1 kPa and applied pressures of 50 and 200 kPa was due to the formation of relict structural pores during compaction. The relict structural pores resulted from partial distortion of the structural pores within the original aggregates. These relict structural pores still had the morphology of structural pores on BESI, but they were accessible to mercury through the necks of textural pores identified as lacunar pores.Results also indicate that massive structure frequently seen in the field for these soils and interpreted as resulting either from structural collapse during rewetting or from compaction actually resulted mainly from wheel compaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1995.tb01334.x
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  • 6
    Electronic Resource
    Electronic Resource
    Three-dimensional analysis of a loamy-clay soil using pore and solid chord distributions (1996)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 47 (1996), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Examples of pore and solid chord distributions obtained for ideal porous media are presented, and the distributions of the porous and solid phases of a soil have been studied by pore and solid chord distributions. Serial sections, 100 μm apart, were cut in a soil core, impregnated with resin, and images were obtained of them. The 2D images from 160 sections were used to build a 3D reconstruction of the core. The initial 2D images, the 3D reconstructed medium and 2D computed images from the latter were studied. We found that the solid matrix of the particular soil is homogeneous and isotropic at the scale studied, and it could be characterized with a single 2D image. For pores ranging from 500 μm to 2 mm we also found similar pore chord distributions for the 2D images in the three orthogonal directions and the 3D medium. A single 2D image can be used to study these pores. For larger pores more than one 2D image is required, and we showed that eight 2D images are sufficient to describe these pores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.1996.tb01844.x
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