No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Quantitative Three-dimensional Characterization of The Pore Network and Soil Structure Using Microfocus X-ray Computed Tomography
Abstract
The geometry of pore space is one of the key features in understanding transport of water and solutes. For soils where macropores are present over the whole length of the soil profile and simulations at the pore scale are used to determine the macroscopic soil hydraulic properties the quantitative characterization of the soil structure and pore network is extremely important. The application of microfocus X-ray computed tomography (tCT) provides a possi- bility for a non-destructive, three-dimensional morphological characterization of soil structure and the pore network at a microscale level. Two heterogeneous sandy loam soil cores (100 cm3) are scanned using microfocus X-ray computed tomography with a resolution of approximately 100 tm. The samples are chosen on the basis of their different macroscopic hydraulic properties that are determined in an inverse optimiza- tion procedure using multistep outflow and direct hydraulic measurements data. The complete water-filled pore space is derived from tCT images of saturated soil sam- ples. Scanning at two different energies (dual energy approach) gives information on the water-air distribution within the pore network at different successive soil pres- sure head conditions. This information can explain drainage or infiltration behavior of the pore network. Moreover 3D reconstructed images is converted to different bi- nary images by choosing appropriate threshold values to obtain pore networks with different degrees of connectivity. Several other geometrical properties such as pore volume, pore area of the derived pore network are then calculated. Furthermore, pore connectivity parameters such as the Euler Poincaré characteristic are determined. A pore size distribution, which considers the hydraulic diameter of the pores, is based on the techniques of the mathematical morphology, namely erosion and dilatation. This study discusses the derivation of true quantitative images using tCT, which is essential for obtaining good 3D quantitative soil structural information. The obtained results of the characterization of soil structure are compared to the outcome of the multistep outflow experiments.
... Recent applications of computer-based 3-D reconstruction of geomaterials demonstrate the advantages and versatility of this technique. These applications involve using mathematical morphology and X-ray computed tomography to measure pore size distribution in sandy loam soil cores (Herman et al., 2002), quantification of macropore networks in undisturbed soil cores by reconstructing 3-D structure from 2-D matrices generated by an X-ray CAT scanner (Perret et al., 1999 ), and characterization of reservoir rocks in terms of chamberand-throat networks (Tsakiroglou and Payatakes, 2000), A three-dimensional digital image consists of a stack of two-dimensional slices or images. Generally, there are two ways to collect these 2-D images: non-destructive and destructive methods. ...
... the pore space which is dependent on the pore radius, to measure pore topology directly. In the network model, the concepts of pore bodies and pore throats are omitted. It is believed that the model is more suitable for natural soil that contain large pores, which are continuous over a considerable length (i.e. root channels or burrows of animals). Herman et al (2002) studied the pore size distribution and connectivity of three heterogeneous sand loam soil cores using X-ray CT with a resolution of approximately 50 micron. Mathematical morphology (erosion and dilation with spheres of growing diameters) was performed on the binary volumes. It was shown from the pore size distribution that the amount of ...
In the last decade, a significant amount of research has been performed to characterize the microstructure of unsheared and sheared triaxial sand specimens to advance the understanding of the engineering behavior of soils. However, most of the research has been limited to two-dimensional (2-D) image analysis of section planes that resulted in loss of information regarding the skeleton of the soil (pore structure) and other attributes of the three-dimensional (3-D) microstructure. In this research, the 3-D microstructures of triaxial test specimens were, for the first time, characterized. A serial sectioning technique was developed for obtaining 3-D microstructure from 2-D sections of triaxial test specimens. The mosaic technique was used to get high-resolution large field of view images. Various 3-D characterization parameters were used to study the microstructures of the specimens. To study the preparation method induced variation in soil microstructure, two specimens prepared with air pluviation and moist tamping methods were preserved with epoxy impregnation. A coupon was cut from the center of each specimen, and following a serial sectioning and image capture process, the 3-D structure was reconstructed. To study the evolution of structure during shearing tests, two additional specimens prepared to the same initial conditions with the same methods were subjected to axial compression loading under constant confining pressure up to an axial strain level of 14%. After shearing, the structure of these specimens were also preserved and analyzed following the same procedures as the unsheared specimens. The evolution of the pore structures was investigated accordingly. It was found that generally, moist tamped specimens were initially less uniform but had a more isotropic structure than air pluviated specimens. The standard deviations of 2-D local void ratio and 3-D pore size in dilated regions of sheared air pluviated and moist-tamped specimens were found to be smaller than those of as-consolidated specimens at a given void ratio. Tortuosity decreased with increasing pore size. It was also evident that the soil structures evolved differently depending on the initial structure. Comparison between 2-D and 3-D results indicated that it is not sufficient to use 2-D section information for characterizing some microstructural features. Ph.D. Committee Chair: Frost, J. David; Committee Member: Gokhale, Arun. N; Committee Member: Mayne, Paul W.; Committee Member: Rix, Glenn J.; Committee Member: Tsai, James
... Erosion followed by dilation of voxels with the same diamond-shaped structuring element of increasing diameter removes cracks which are smaller than the structuring element. The derivative of the cumulative porosity derived at each step yielded crack aperture distributions (Herman et al., 2002; Vogel et al., 2005).Figure 3b) shows by far the widest aperture range. Low bentonite content samples (Figures 3a and 3c) have finer and less cracks. ...
Development and evolution of desiccation cracks in bentonite-sand mixtures are strongly dependent on the physico-chemical boundary conditions. To investigate effects of solution chemistry and mixture bentonite content on cracking behavior, we conducted well-controlled dehydration experiments and applied X-ray Computed Tomography (CT) in conjunction with Mathematical Morphology to visualize and quantify geometrical features of evolving crack networks. Sampleswith varying bentonite content were saturated with 0.05 and 0.5 molar NaCl solutions, dehydrated under constant temperature, and scanned with X-ray CT at constant time intervals. Obtained 3-D images were analyzed based on Mathematical Morphology to quantify crack porosity, specific surface area, and aperture distributions of crack networks.
... A simple voxel counting algorithm provided as part of the SkyScan Analyzer soft ware package was used to determine sample porosities from threedimensional , binarized volume data. Estimates for pore-size distributions were obtained from the three-dimensional binary representation of pores on a rectangular grid with the help of mathematical morphology operations (i.e., erosion and dilation) (Vogel and Roth, 2001; Herman et al., 2002; Pierret et al., 2002). ...
Recent advances in benchtop Micro-Computed Tomography (Micro-CT) provided the motivation to thoroughly evaluate and optimize scanning, image reconstruction/segmentation and pore space analysis capabilities of a SkyScan 1172 Micro-CT system and associated SkyScan Analyzer soft ware package (SkyScan, Belgium). To demonstrate applicability to soil research the project was focused on determination of porosities and pore-size distributions of two Brazilian Oxisols from segmented computed tomography (CT)-data. Effects of metal filters and various acquisition parameters (e. g., total rotation, rotation step, and radiograph frame averaging) on image quality and acquisition time were evaluated. Impacts of sample size and scanning resolution on CT-derived porosities and pore-size distributions were illustrated. Best image quality was achieved when an aluminum/copper filter (0.5/0.04 mm thickness) was positioned between sample and x-ray detector, the sample was rotated 360 degrees in 0.3 degrees steps and the number of averaged projections per rotation step was larger than 15. As with all other CT systems there was a tradeoff between maximum observable sample volume and achievable resolution. Even for soil samples scanned at the highest considered resolution of 3.7 mu m (1.0 mu m is the maximum achievable resolution) it was apparent that CT-derived porosities vastly underestimated physically measured apparent porosity values. In addition, it was shown that dense mineral particles can be discriminated from slightly attenuating elements and minerals. While image acquisition and reconstruction yielded excellent grayscale CT-data, the supplied soft ware lacked advanced image segmentation algorithms and morphometric pore space analysis capabilities.
... To automatically determine crack aperture distributions, crack porosities, and crack specific surface areas from corrected binary data algorithms were coded in MATLAB® (The MathWorks, Inc., Natick, MA). The crack aperture distributions (CAD) for three-dimensional crack networks were extracted with the help of mathematical morphology operations (Herman et al., 2002; Horgan, 1998; Peters, 1997; Pierret et al., 2002; Vogel and Roth, 2001). A simple voxel counting algorithm was applied to derive crack porosity as the sum of white voxels divided by the total number of voxels within a sample. ...
ResearchGate has not been able to resolve any references for this publication.