Three Dimensional Measurements of Pore Morphological and Hydraulic Properties (original) (raw)
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Bioimaging, 1997
Skip to Main Content. ...Knowledge of flow in porous media can be improved by analyzing three-dimensional (3-D) images of the water distribution in a soil. We report on such a study using computed tomography (CT) scanning of a clay soil sample first in dry conditions. Then, after an infiltration experiment, by scanning the sample again in wet conditions. We used test phantoms to determine the optimal scanning parameters to obtain images with a bimodal gray value distribution with high contrast and small standard deviation. We also determined the effect of slice thickness and reconstruction algorithm on the restoration and segmentation of the images. For a good 3-D representation of the pore space we scanned the slices adjacently at an axial resolution of 1 mm and a pixel size of 0:27 0:27 mm2. The high contrast between air in the pores and the clay background allowed a global thresholding for the segmentation whereby the connectivity and topology of the pore networks is conserved. From the difference between the images of the dry sample and the wet sample we determined the water content distribution. We used the image data for measurements of the water distribution to study the relation between the structure of the pore networks and water flow.
Geoderma, 2010
This study investigates the use of 3D soil pore characteristics (volume, surface area, and tortuosity) for prediction of saturated hydraulic conductivity (K s). The pore characteristics were determined by cluster labeling of X-ray CT images and random-walk simulations of 3D pore space. The flow characteristics of the four soil cores were measured in the laboratory pre-and post-CT imaging. The predicted values of K s were arrived at through the use of Darcy's equation and a modified Poiseuille equation. For comparison the 2D pore characteristics were determined from individual slice of X-ray CT imagery, and fed into three established methods of predicting K s. The predicted K s by the proposed method exhibited a positive correlation to both pre-and post-imaging measured K s , and attained a greater correlation than the 2D K s prediction.
Eurasian Soil Science, 2019
The development of tomographic studies of soil pore space in Russian soil science in 2011-2018 is discussed. In several years, these studies have evolved from the qualitative description of pores in some soils from the European part of Russia to the quantitative functional assessment of soil pore space on the bases of 3D tomographic models. Three stages of tomographic studies of soil pores can be distinguished: (1) qualitative analysis of pore space as a spatial-geometric characteristic of soil structure and as a component of the general analysis of soil morphology; (2) the obtaining of quantitative morphometric data on the shape, size, and orientation of soil pores and combined analysis of these tomographic data and data on the physical soil properties; and (3) the use of calculated tomographic parameters in the study of hydrological and physicomechanical properties of soils important for both theoretical and applied aspects of soil science. In recent years, the research has been focused on the assessment of the relationships between tomographic parameters of soil pore space and traditional soil hydrological constants, possibility of calculating the water retention curve and water conductivity function from the tomographic parameters of soil pore space, and on the quantitative assessment and prediction of soil degradation on the basis of tomographic data. The solution to these problems will make it possible to explain the physical phenomena controlling soil hydrological characteristics and to substantiate the use of tomographic data in applied soil science, soil hydrology, and agrophysics.
The soil pore system as an indicator of soil quality
The need to reduce the environmental impact of agricultural activities and to control degradation of soil structure is one of the main aims of land management, especially in vulnerable environments. Intensive cultivation of some agricultural soils can lead to deterioration in soil structure and other physical properties of the soil and, consequently, decreased crop yields. The most important modifications of soil structure mainly involve changes in soil porosity. Therefore, measurements of this physical property can help to quantify the impact of management practices on soil. This is now possible because of the increasing use and availability of the technique of image analysis which makes possible the automated measurement of soil porosity on thin sections or impregnated soil blocks prepared from undisturbed soil samples. Soil porosity is, therefore, the best indicator of soil structure quality. Quantification of the pore space in terms of shape, size, continuity, orientation and arrangement of pores in soil allows us to define the complexity of soil structure and to understand its modifications induced by management practices. In this way, we can identify those management practices that are more compatible with environmental protection. Characterisation of the pore system provides a realistic basis for understanding the retention and movement of water in soil. Significant correlations have been found between elongated continuous transmission pores and hydraulic conductivity that can be useful in the development and improvement of models for predicting water movement. Soil porosity shows a strong correlation with penetration resistance: a decrease of porosity is generally associated with an increase of penetration resistance. The pore shape and size distribution are also strictly related to chemical, biochemical and biological properties, like enzyme activity, and root growth.
Transport in Porous Media, 2004
This paper presents a simple geometrical pore model designed to relate characteristic pore radii of the porous network of soils with macroscopic infiltration parameters. The model composed of a stack of spherical hollow elements is described with two radii values: the pore access radius and the actual pore radius. The model was compared to cylindrical pore models and its mathematical consistency was assessed. Soil sorptivity S and the second parameter A of the Philip infiltration equation (1957), have been determined by numerically simulated infiltration. A diagram and an empirical relation have been set in order to relate the pore access and pore radii to the infiltration parameters S and A. The consistency of the model was validated by comparing the predicted sorptivity and hydraulic conductivity values, with the widely used unsaturated soil hydraulic functions (van Genuchten, 1980). The model showed good agreement with experimental infiltration data, and it is therefore concluded that the use of a model with two radii improves the relation between microscopic pore size and macroscopic infiltration parameters.
Soil Science Society of America Journal, 2017
Soil pores form interconnected networks that directly or indirectly in uence transport processes in soils. There is great interest in estimating pore properties such as size and shape from three-dimensional (3D) images as a way of understanding linkages between structure and function. This work evaluates the applicability of an approach to measure pore-size distributions (PSDs) from 3D images of four soils with contrasting physical properties. Images were obtained with a benchtop X-ray microtomograph system at spatial resolutions of 4, 6, 12, and 30 m by varying the size of the samples from 0.5 cm to about 4 cm in diameter. Pore-size distributions obtained at each image resolution were tted with lognormal distribution functions with r 2 ranging from 0.81 to 0.98. The four PSDs for a given soil were combined by identifying crossover points in the lognormal distributions. When pore sizes where imaged at more than one resolution, the criterion followed to eliminate redundant information was that large pore sizes are better represented in low resolution images of large sample sizes, and vice versa. Pore-size data from four truncated PSDs were tted with a lognormal distribution function to obtain a nal (global) PSD for each soil. Global PSDs obtained with the image-based approach correlated well with PSDs measured by mercury intrusion porosimetry and also with PSDs derived from soil water retention curves, showing potential for application of this image-based approach to soils.
Geoderma, 2017
The pore size distribution (PSD) of the void space is widely used to predict a range of processes in soils. Recent advances in X-ray computed tomography (CT) now afford novel ways to obtain exact data on pore geometry, which has stimulated the development of algorithms to estimate the pore size distribution from 3D data sets. To date there is however no clear consensus on how PSDs should be estimated, and in what form PSDs are best presented. In this article, we first review the theoretical principles shared by the various methods for PSD estimation. Then we select methods that are widely adopted in soil science and geoscience, and we use a robust statistical method to compare their application to synthetic image samples, for which analytical solutions of PSDs are available, and X-ray CT images of soil samples selected from different treatments to obtain wide ranging PSDs. Results indicate that, when applied to the synthetic images, all methods presenting PSDs as pore volume per class size (i.e., Avizo, CTAnalyser, BoneJ, Quantim4, and DTM), perform well. Among them, the methods based on Maximum Inscribed Balls (Bone J, CTAnalyser, Quantim4) also produce similar PSDs for the soil samples, whereas the Delaunay Triangulation Method (DTM) produces larger estimates of the pore volume occupied by small pores, and Avizo yields larger estimates of the pore volume occupied by large pores. By contrast, the methods that calculate PSDs as object population fraction per volume class (Avizo, 3DMA, DFS-FIJI) perform inconsistently on the synthetic images and do not appear well suited to handle the more complex geometries of soils. It is anticipated that the extensive evaluation of method performance carried out in this study, together with the recommendations reached, will be useful to the porous media community to make more informed choices relative to suitable PSD estimation methods, and will help improve current practice, which is often ad hoc and heuristic.
Experimental techniques for multi-scale description of soil fabric and its dual pore network
2012
Fabric affects many aspects of soil mechanical behaviour. When transport processes are of concern, its dual, the pore network, is the key aspect ruling the soil properties of interest. In this chapter, a review of a few widely used techniques, currently adopted to analyse the pore network at increasing scale, is presented, namely mercury intrusion porosimetry, environmental scanning electron microscopy and electrical resistivity tomography. Details on the techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. The results highlight how these techniques provide an insight into the pore network, and how they can be usefully exploited in the understanding of different hydro-electromechanical processes ordinarily observed at the phenomenological scale. Attention is focused on unsaturated soils with reference to water retention properties, micro / macrostructure interaction, and role of sample heterogeneity.