A tomographic imagery segmentation methodology for three-phase geomaterials based on simultaneous region growing

Abstract

X-ray computed tomography is a powerful nondestructive 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 micron resolutions. Consequently, X-ray microcomputed tomography opens perspectives for the analysis of the fabric of multiphase geomaterials such as soils, concretes, rocks and 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 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 method requires 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.

Local water-retention behaviour of sand during drying and wetting process observed by micro x-ray tomography with trinarisation

“…Furthermore, the x-ray CT images are trinarised into the soil phase, pore water phase and pore air phase. Trinarisation technique of CT images for partially saturated sand is required to take into account the partial volume effect: in particular, voxels shared by the soil phase and the air phase are wrongly identified as the water phase since the mixture of the soil and the air often gives CT value similar to the water (Hashemi et al 2014, Higo et al 2014.…”

Computational modelling of crack-induced permeability evolution in granite with dilatant cracks

“…Possible future developments also relate to the use of real CT scan data of geomaterials [77,91] to generate microstructural RVEs, or specific advanced RVE generation techniques [92], in combination with advanced discretisation techniques [93,94]. Influence of the confining pressure on stress-induced permeability evolution Figure 6: Influence of the factor f on the obtained macroscopic permeability evolution for the RVE subjected to a deviatoric triaxial stress state at a confining stress of 10 MPa.…”

Grain scale mechanisms for capillary collapse in a loose unsaturated pyroclastic soil

“…misalignment of source, detector and axis of rotation; detector defects; anomalous bright pixels in the radiographs). The reconstruction procedure provides several contiguous cross-sections, either vertical or horizontal, which allows 3D visualization of the selected features and the quantification of the 3D volumes After the body reconstruction, the regions occupied by each phase can be recognized by visual interpretationobtaining qualitative estimates -, or using computational methods to obtain quantitative results [12]. The recognition of the phases which constitutes the object is commonly called "segmentation".…”

“…Consequently, a single threshold of the grey value is not sufficient to distinguish each phase properly. To overcome the difficulties related to the CT images of unsaturated soils, a kind of region growing method is used [12]. The method was developed as one of regionbased segmentation methods for digital images [14], and postulates that the neighboring voxel within one region have similar values [15].…”