The goal of this project is to develop an analysis environment for high-resolution CT scans of porous materials. This environment will integrate methods to compute the topological structure of the pore space and use image processing algorithms as well as geometric algorithms to exactly assess geometrical properties. Furthermore, the characteristics of the extracted structures will be investigated and determined. The visualization software Amira provides the framework for the analysis tools.

Background

In cooperation with our project partners, suffosion processes in porous soil will be investigated [Semar et al. 2009]. The suffosion processes comprise the transport of mobile particles through the pore space induced by water flow. These transports cause changes in the permeability and porosity of the soil. The consequences are less resistance against external load and settlement of the soil. The overall project goal is the determination of mobile particles and their transport paths as well as simulations of suffosion processes. To assess the soil's spatial structures, CT data of soil samples and synthetic data from simulations are used. In order to obtain information on the soil structure, we analyze particle and pore structures as well as transport possibilities therein. 

Particle Structure

Initial volume (grey) and extracted particles (colored)

Fig. 1: Initial volume (grey) and extracted particles (colored)

To extract the particle structure from the CT data, we provide a processing pipeline [Homberg et al. 2009]. First, we use image filters and a threshold method for preprocessing and segmenting the particle structure. Afterwards, we apply morphological filters and a watershed based method for post-processing and splitting connected particles. Parameters such as size, volume, number, and positions can be computed from the segmentation results. Finally, application specific quantities like statistical distributions and the spatial distribution of particles can be derived from these parameters.

Pore Structure

The segmentation results also provide a basis for analyzing the pore space. Interesting elements of the pore space are pores, pore paths and pore constrictions. These elements can be described by the topology of the distance transform containing the distances to the boundaries of the segmented particles. The elements of the pore structure and other parameters e.g. radii can be extracted from CT data and used to construct a graph representing the pore space. Here, we apply a Voronoi-like approach to obtain these structures [Homberg et al. 2012]. The idea is a watershed propagation of the labeled particle regions based on the distance transform. The pore graph is constructed from all points of cell boundaries with at least three adjoining particle regions. This approach allows us to represent the topology of the pore space by a compact pore graph. To extract the pore bodies, again, we apply a watershed-based method marked by the extracted pore centers of the pore graph. These results, in turn, can be used to derive parameters (pore constriction distribution, connectedness quantities) for simulating suffosion processes.

Fig. 2: Extracted elements of the pore space. (a) Detail of the distance map and constructed pore graph; (b) Two pore bodies and pore graph within particles; (c) Pore graph within the particle structure.

The constructed pore graph allows us to use this compact representation for an efficient analysis of transport possibilities. We apply a method that successively blocks the critical percolation edges in order to determine size-dependent transport possibilities. Here, an iterative min-cut adaption filters the maximal radius that holds the top-bottom connection and finds and cuts the edges of that radius which particles have to pass. The described process computes a decomposition of the pore graph into a top-subgraph and a bottom-subgraph connected by the critical edges in each iteration. These results can be used to estimate a size-dependent cumulative number of possibilities as well as an upper bound of the largest mobile particle.

Fig. 3: (a) Radius-filtered pore graph (red) within the initial pore graph (grey); (b) Top-bottom decomposition of the transport possibilities for a chosen particle size; (c) Possible transport path and its critical edge (green) through the particles; (d) Transport path and its channel of pores.

Publications

2018
Merging criteria for defining pores and constrictions in numerical packing of spheres Granular Matter, 20(37), 2018 (preprint available as ZIB-Report 18-25) Feda Seblany, Ulrike Homberg, Eric Vincens, Paul Winkler, Karl Josef Witt PDF (ZIB-Report)
BibTeX
DOI
Image-Based Analysis of Pore and Particle Structures
2017
Merging criteria for the definition of a local pore and the CSD computation of granular materials Proceedings of the 25th meeting of the Working Group on Internal Erosion in embankment dams and their foundations, pp. 150-159, 2017, ISBN: 978-90-827468-1-5 | 978-90-827468-0-8 (preprint available as ZIB-Report 18-09) Feda Seblany, Ulrike Homberg, Eric Vincens, Paul Winkler, Karl Josef Witt PDF (ZIB-Report)
BibTeX
Image-Based Analysis of Pore and Particle Structures
2015
Approaches to Determine the Constriction Size Distribution for Understanding Filtration Phenomena in Granular Materials Acta Geotechnica, 10(3), pp. 291-303, 2015 (preprint available as ) Eric Vincens, Karl Josef Witt, Ulrike Homberg BibTeX
DOI
Image-Based Analysis of Pore and Particle Structures
2014
Definition, Extraction, and Validation of Pore Structures in Porous Materials Topological Methods in Data Analysis and Visualization III, pp. 235-248, Peer-Timo Bremer, Ingrid Hotz, Valerio Pascucci, Ronald Peikert (Eds.), Springer, 2014 (preprint available as ZIB-Report 13-56) Ulrike Homberg, Daniel Baum, Alexander Wiebel, Steffen Prohaska, Hans-Christian Hege PDF (ZIB-Report)
BibTeX
DOI
Image-Based Analysis of Pore and Particle Structures
2012
Automatic Extraction and Analysis of Realistic Pore Structures from µCT Data for Pore Space Characterization of Graded Soil Proceedings of the 6th International Conference on Scour and Erosion (ICSE-6), pp. 345-352, 2012 Ulrike Homberg, Daniel Baum, Steffen Prohaska, Ute Kalbe, Karl Josef Witt BibTeX
Image-Based Analysis of Pore and Particle Structures
2011
Describing and Analyzing the Dual Structures of Porous Media Proc. 3D-Microstructure Meeting, Frank Mücklich, Philipp Slussallek, Katja Schladitz (Eds.), pp. 24-25, 2011 Ulrike Homberg, Daniel Baum, Steffen Prohaska BibTeX
Image-Based Analysis of Pore and Particle Structures
2010
Identification of Descriptive Parameters of the Soil Pore Structure using Experiments and CT Data Proceedings of the 5th International Conference on Scour and Erosion (ICSE-5), pp. 397-407, 2010 Richard Binner, Ulrike Homberg, Steffen Prohaska, Ute Kalbe, Karl Josef Witt BibTeX
Image-Based Analysis of Pore and Particle Structures
2009
Conditions for Suffosive Erosion Phemomena in Soils – Concept and Approach Workshop Internal Erosion, pp. 29-35, Vol.21, Schriftenreihe Geotechnik, 2009 Olivier Semar, Richard Binner, Ulrike Homberg, Ute Kalbe, Tobias Mehlhorn, Steffen Prohaska, Volker Slowik, Karl Josef Witt BibTeX
Image-Based Analysis of Pore and Particle Structures
Determining Geometric Grain Structure from X-Ray Micro-Tomograms of Gradated Soil Workshop Internal Erosion, pp. 37-52, Vol.21, Schriftenreihe Geotechnik, 2009 Ulrike Homberg, Richard Binner, Steffen Prohaska, Vincent J. Dercksen, Anja Kuß, Ute Kalbe BibTeX
Image-Based Analysis of Pore and Particle Structures
Modelling and Analysis of Particle and Pore Structures in Soils Workshop Internal Erosion, pp. 53-60, Vol.21, Schriftenreihe Geotechnik, 2009 Tobias Mehlhorn, Steffen Prohaska, Ulrike Homberg, Volker Slowik BibTeX
Image-Based Analysis of Pore and Particle Structures