With the recent developments of full field measurements, it has become possible to do experiments... more With the recent developments of full field measurements, it has become possible to do experiments on a soil specimen, and perform measurements at different scales. This progress has allowed greater understanding for all the processes that occur within the soil, and also created better environment to observe these mechanisms in 3D. This PhD work aims to characterize water retention and hydro-mechanical behaviours of unsaturated Hostun sand at the grain scale. To achieve this goal, water retention and triaxial tests were performed and a set of experimental and image processing tools was developed and used for the two series of tests. X-ray computed tomography set up available at 3SR Laboratory in Grenoble University was used to generate 3D images of the unsaturated soil microstructure non-destructively. A developed region growing systematic technique (trinarization technique) was used to allow the separation of the phases (i.e., grains, water and air) in the 3D images, and performing ...
The recent implementations of X-ray computed tomography, to analyze different responses and behav... more The recent implementations of X-ray computed tomography, to analyze different responses and behaviours of various soils, are based on full-field measurements allowing to obtain morphological information at different scales. With the huge volume of details available from this technique it has become important to develop numerical key tools that allow to treat X-ray images with more analytical view, and automate the process of identification of all the present elements. In this study, a developed code of segmentation is presented, in order to extract the maximum possible information, that allow to investigate porosity and degree of saturation, at grain scale, through the study of water retention behaviour (WRB) of unsaturated sand. X-ray images, of a resolution of 7.5μm, were segmented and then used to validate this code. All the interpretations associated to this method of segmentation are discussed and can be adjusted to fit any future study.
ABSTRACT X-Ray Computed Tomography (X-Ray CT) is a powerful non-destructive technique used in man... more ABSTRACT X-Ray Computed Tomography (X-Ray CT) is a powerful non-destructive technique used in many domains to obtain the three-dimensional representation of objects, starting from the reconstitution of two-dimensional images of radiographic scanning. This technique is now able to analyze objects within a few microns resolution. Consequently, X-Ray micro-computed tomography (X-Ray μCT) opens perspectivesfor the analysis of the fabric of multi-phase geomaterials such as soils, concretes, rocks or ceramics. To be able to characterize the spatial distribution of the different phases in such complex and disordered materials, automated phase recognition has to be implemented through image segmentation. A crucial difficulty in segmenting images lies in the presence of noise in the obtained tomographic representation, making it difficult to assign a specific phase to each voxel (vx) of the image. In the present study, simultaneous region growing is used to reconstitute the three-dimensional segmented image of granular materials. First, based on a set of expected phases in the image, regions where specific phases are sure to be present are identified, leaving uncertain regions of the image unidentified. Subsequently, the identified regions are grown until growing phases meet each other with vanishing unidentified regions. The methodrequires a limited number of manual parameters that are easily determined. The developed method is illustrated based on three applications on granular materials, comparing the phase volume fractions obtained by segmentation with macroscopic data. It is demonstrated that the algorithm rapidly converges and fills the image after a few iterations.
With the recent developments of full field measurements, it has become possible to do experiments... more With the recent developments of full field measurements, it has become possible to do experiments on a soil specimen, and perform measurements at different scales. This progress has allowed greater understanding for all the processes that occur within the soil, and also created better environment to observe these mechanisms in 3D. This PhD work aims to characterize water retention and hydro-mechanical behaviours of unsaturated Hostun sand at the grain scale. To achieve this goal, water retention and triaxial tests were performed and a set of experimental and image processing tools was developed and used for the two series of tests. X-ray computed tomography set up available at 3SR Laboratory in Grenoble University was used to generate 3D images of the unsaturated soil microstructure non-destructively. A developed region growing systematic technique (trinarization technique) was used to allow the separation of the phases (i.e., grains, water and air) in the 3D images, and performing ...
The recent implementations of X-ray computed tomography, to analyze different responses and behav... more The recent implementations of X-ray computed tomography, to analyze different responses and behaviours of various soils, are based on full-field measurements allowing to obtain morphological information at different scales. With the huge volume of details available from this technique it has become important to develop numerical key tools that allow to treat X-ray images with more analytical view, and automate the process of identification of all the present elements. In this study, a developed code of segmentation is presented, in order to extract the maximum possible information, that allow to investigate porosity and degree of saturation, at grain scale, through the study of water retention behaviour (WRB) of unsaturated sand. X-ray images, of a resolution of 7.5μm, were segmented and then used to validate this code. All the interpretations associated to this method of segmentation are discussed and can be adjusted to fit any future study.
ABSTRACT X-Ray Computed Tomography (X-Ray CT) is a powerful non-destructive technique used in man... more ABSTRACT X-Ray Computed Tomography (X-Ray CT) is a powerful non-destructive technique used in many domains to obtain the three-dimensional representation of objects, starting from the reconstitution of two-dimensional images of radiographic scanning. This technique is now able to analyze objects within a few microns resolution. Consequently, X-Ray micro-computed tomography (X-Ray μCT) opens perspectivesfor the analysis of the fabric of multi-phase geomaterials such as soils, concretes, rocks or ceramics. To be able to characterize the spatial distribution of the different phases in such complex and disordered materials, automated phase recognition has to be implemented through image segmentation. A crucial difficulty in segmenting images lies in the presence of noise in the obtained tomographic representation, making it difficult to assign a specific phase to each voxel (vx) of the image. In the present study, simultaneous region growing is used to reconstitute the three-dimensional segmented image of granular materials. First, based on a set of expected phases in the image, regions where specific phases are sure to be present are identified, leaving uncertain regions of the image unidentified. Subsequently, the identified regions are grown until growing phases meet each other with vanishing unidentified regions. The methodrequires a limited number of manual parameters that are easily determined. The developed method is illustrated based on three applications on granular materials, comparing the phase volume fractions obtained by segmentation with macroscopic data. It is demonstrated that the algorithm rapidly converges and fills the image after a few iterations.
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Papers by Ghonwa KHADDOUR