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UBC Theses and Dissertations

Application of computed tomography for visualizing three-dimensional fabric and microstructure of Fraser River Delta silt Wesolowski, Michelle


A research program was undertaken to visualize and quantify the three-dimensional nature of fabric and microstructure of natural silts with the objective of better understanding the influence of these factors on macroscopic monotonic and cyclic soil behaviour. The development of technology for the visualizations using X-ray micro-computed tomography (CT) formed a key task. Natural, low-plastic Fraser River Delta silt available from the Lower Mainland area of British Columbia was used as the geomaterial for the study. In order to capture a representative elemental volume for analysis in micro-CT, experimentation was undertaken to identify the appropriate method(s) to obtain sub-samples of specimens from relatively larger undisturbed samples or reconstituted specimens of silt. Thin-walled (0.135-mm thick) plastic tubing (5.0-mm diameter) was chosen to obtain sub-samples of silt that would be compatible with micro-CT scanning apparatus and procedures. The potential for sample preservation using resin impregnation was also explored. A very low viscosity resin which cured at room temperature under anaerobic conditions provided a novel way to successfully preserve samples. Preliminary observations suggest that there is minimal disturbance to the internal fabric and microstructure within the core of the specimen sub-samples. A collaboration with three X-ray micro-CT laboratories allowed for scanning of the silt sub-samples to voxel resolutions ranging from 0.869 to 3.38 µm. The three-dimensional datasets were then post-processed using commercially available software. A systematic study was conducted to choose the “non-local means” filter which reduced image noise while preserving digital grain edges. Particle segmentation of the images was undertaken using the watershed methodology, which led to successful digital grain size distribution matching with typical laboratory data. Initial quantitative analysis indicates that the void ratio as well as particle contact angle distribution diagrams can be formulated for silt-sized material. Quantification of particle shape including sphericity, roundness, and aspect ratio, and their relation to specimen mineralogy, was also explored. The research work demonstrated that X-ray micro-CT technology has a strong potential to be a viable method for three-dimensional visualization of silts.

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